Chapter 17 Electrodiagnostics (Part II)

Question 1

PERIPHERAL NEUROPATHY
Peripheral neuropathy is a generalized dysfunction of the peripheral nerves. The distal segments of the nerves are usually more affected than the proximal segments. Thus, the longer the nerve, the more it is usually affected. Peripheral neuropathies typically occur in a “_________ and _________” distribution, affecting the feet and hands with numbness, pain, or pares-thesias.

Answer 1

PERIPHERAL NEUROPATHY
Peripheral neuropathy is a generalized dysfunction of the peripheral nerves. The distal segments of the nerves are usually more affected than the proximal segments. Thus, the longer the nerve, the more it is usually affected. Peripheral neuropathies typically occur in a “stocking and glove” distribution, affecting the feet and hands with numbness, pain, or pares-thesias.

Question 2

PERIPHERAL NEUROPATHY
Electrodiagnostic studies (NCS/EMG) are used to determine the presence of peripheral neuropathy and can help to identify its characteristics and severity. Peripheral neuropathy is classified based on the types of _________ involved (sensory or motor), the primary pathology affecting the component of the _________ (axonal or demyelinating), and its _________ (segmental or uniform).

Answer 2

PERIPHERAL NEUROPATHY
Electrodiagnostic studies (NCS/EMG) are used to determine the presence of peripheral neuropathy and can help to identify its characteristics and severity. Peripheral neuropathy is classified based on the types of fibers involved (sensory or motor), the primary pathology affecting the component of the nerve (axonal or demyelinating), and its extent (segmental or uniform).

Question 3

PERIPHERAL NEUROPATHY
When performing electrodiagnostic testing, both sensory and motor nerves must be tested in at least _________ extremities to differentiate between single entrapment neuropathy and a generalized process. Relevant findings must be found in at least three extremities to be diagnosed as a peripheral neuropathy. Early in the progression of peripheral neuropathy, changes may not be seen in the _________ extremity.

Answer 3

PERIPHERAL NEUROPATHY
When performing electrodiagnostic testing, both sensory and motor nerves must be tested in at least three extremities to differentiate between single entrapment neuropathy and a generalized process. Relevant findings must be found in at least three extremities to be diagnosed as a peripheral neuropathy. Early in the progression of peripheral neuropathy, changes may not be seen in the upper extremity.

Question 4

PERIPHERAL NEUROPATHY
Nerve Conduction Studies
Sensory NCS: SNAPs may be reduced.
If axonal: _________ of SNAP will be reduced or unobtainable.
If demyelinating: SNAP can have an increased _________ (decreased _________); demyelination may result in loss of SNAP through conduction block (neurapraxia).

Answer 4

PERIPHERAL NEUROPATHY
Nerve Conduction Studies
Sensory NCS: SNAPs may be reduced.
If axonal: amplitude of SNAP will be reduced or unobtainable.
If demyelinating: SNAP can have an increased latency (decreased CV); demyelination may result in loss of SNAP through conduction block (neurapraxia).

Question 5

PERIPHERAL NEUROPATHY
Motor NCS:
If axonal: _________ of CMAP may be affected or unobtainable.
If demyelinating: CMAP may have increased distal _________ or slowing _________. (_________ less than _________% of the lower limit of normal suggests a demyelinating neuropathy.) Conduction block may also cause decreased _________.

Answer 5

PERIPHERAL NEUROPATHY
Motor NCS:
If axonal: amplitude of CMAP may be affected or unobtainable.
If demyelinating: CMAP may have increased distal latency or slowing CV. (CV less than 80% of the lower limit of normal suggests a demyelinating neuropathy.) Conduction block may also cause decreased CMAP.

Question 6

PERIPHERAL NEUROPATHY
Uniform versus segmental: Assessed by location of slowing CV. If segmental, some fibers will travel slower than others and the CMAP will be dispersed, with a _________ duration and _________ amplitude (temporal dispersion). If uniform, all fibers are slowed, which will result in a uniform slowing of CV, prolonged latencies, and normal duration and amplitude NCS.

Answer 6

PERIPHERAL NEUROPATHY
Uniform versus segmental: Assessed by location of slowing CV. If segmental, some fibers will travel slower than others and the CMAP will be dispersed, with a longer duration and lower amplitude (temporal dispersion). If uniform, all fibers are slowed, which will result in a uniform slowing of CV, prolonged latencies, and normal duration and amplitude NCS.

Question 7

PERIPHERAL NEUROPATHY
Note that late responses (_________ waves and _________-reflexes) assess both the proximal and distal segments of a peripheral nerve and therefore may also be affected. However, findings are nonspecific.

Answer 7

PERIPHERAL NEUROPATHY
Note that late responses (F waves and H-reflexes) assess both the proximal and distal segments of a peripheral nerve and therefore may also be affected. However, findings are nonspecific.

Question 8

PERIPHERAL NEUROPATHY
EMG – Test proximal and distal muscles to assess for axonal neuropathy and rule out additional or concomitant pathology. Findings are usually negative in peripheral neuropathy except in a few cases:
1. _________ _________ neuropathy.
2. Chronic _________ disorders: may see _________.

Answer 8

PERIPHERAL NEUROPATHY
EMG – Test proximal and distal muscles to assess for axonal neuropathy and rule out additional or concomitant pathology. Findings are usually negative in peripheral neuropathy except in a few cases:
1. Axonal motor neuropathy.
2. Chronic neurogenic disorders: may see CRDs.

Question 9

PERIPHERAL NEUROPATHY
Axonal motor neuropathy: affected muscles (usually distal) may demonstrate spontaneous activity (_________ and _________). If an axonal lesion is present, the duration of the disease can be assessed by evaluating chronic changes in MUAPs (increased _________, _________, or large _________ reveals reinnervation and reorganization).

Answer 9

PERIPHERAL NEUROPATHY
Axonal motor neuropathy: affected muscles (usually distal) may demonstrate spontaneous activity (fibs and PSW). If an axonal lesion is present, the duration of the disease can be assessed by evaluating chronic changes in MUAPs (increased duration, polyphasicity, or large amplitude reveals reinnervation and reorganization).

Question 10

PERIPHERAL NEUROPATHY
There are many causes for peripheral neuropathy, including _________ and _________ disorders. These disorders are further typified based on separate classifications of peripheral neuropathy that can be derived using electrodiagnostic studies (Table 17-4).

Answer 10

PERIPHERAL NEUROPATHY
There are many causes for peripheral neuropathy, including genetic and acquired disorders. These disorders are further typified based on separate classifications of peripheral neuropathy that can be derived using electrodiagnostic studies (Table 17-4).

Question 11

PERIPHERAL NEUROPATHY
Plexopathy – The functional anatomy of the brachial plexus can be divided into _________ (roots and trunks) and _________ (cords and peripheral nerves or branches) (Fig. 17-7). The pattern of findings will help to localize the lesion. In general, _________ lesions will cause weakness in a muscle group without affecting the antagonist muscles of that group, whereas _________ lesions will affect _________. Electrodiagnostic testing is a physiological examination, which can help to localize the site of a plexus lesion and provide an evaluation of the prognosis. The unaffected limb should be used as a control to compare nerve responses from the two sides tested.

Answer 11

PERIPHERAL NEUROPATHY
Plexopathy – The functional anatomy of the brachial plexus can be divided into supraclavicular (roots and trunks) and infraclavicular (cords and peripheral nerves or branches) (Fig. 17-7). The pattern of findings will help to localize the lesion. In general, infraclavicular lesions will cause weakness in a muscle group without affecting the antagonist muscles of that group, whereas supraclavicular lesions will affect both. Electrodiagnostic testing is a physiological examination, which can help to localize the site of a plexus lesion and provide an evaluation of the prognosis. The unaffected limb should be used as a control to compare nerve responses from the two sides tested.

Question 12

PERIPHERAL NEUROPATHY
Sensory Studies – _________ NCSs are usually a more sensitive indicator of injury to the plexus than the motor nerve response. The distal latency and CV are usually normal. _________ amplitude reflects the number of functioning axons in continuity with the sensory root cell body. Lesions proximal to the DRG, such as radiculopathy and nerve root avulsions, have normal SNAPs even though sensation may be affected clinically. Lesions distal to the DRG disconnect the sensory nerve cell body from its axons, resulting in decrement or absence of the SNAP. Therefore, differentiation between pre- and postganglionic lesions is extremely important.

Answer 12

PERIPHERAL NEUROPATHY
Sensory Studies – Sensory NCSs are usually a more sensitive indicator of injury to the plexus than the motor nerve response. The distal latency and CV are usually normal. SNAP amplitude reflects the number of functioning axons in continuity with the sensory root cell body. Lesions proximal to the DRG, such as radiculopathy and nerve root avulsions, have normal SNAPs even though sensation may be affected clinically. Lesions distal to the DRG disconnect the sensory nerve cell body from its axons, resulting in decrement or absence of the SNAP. Therefore, differentiation between pre- and postganglionic lesions is extremely important.

Question 13

PERIPHERAL NEUROPATHY
Motor Studies – CMAPs are usually not affected unless the injury is severe. Motor latencies and conduction velocities are usually unaffected. Stimulation at _________ point may reveal slowing if there is a demyelinating lesion in the brachial plexus. CMAP amplitudes may be decreased if there is severe axonal damage. In plexopathies, side-to-side amplitude differences can give an approximation of the degree of axonal injury during the first few months. A 70% decrement in CMAP amplitude correlates to _________% axon loss. Amplitude differences of less than _________% may not be significant.

Answer 13

PERIPHERAL NEUROPATHY
Motor Studies – CMAPs are usually not affected unless the injury is severe. Motor latencies and conduction velocities are usually unaffected. Stimulation at Erb’s point may reveal slowing if there is a demyelinating lesion in the brachial plexus. CMAP amplitudes may be decreased if there is severe axonal damage. In plexopathies, side-to-side amplitude differences can give an approximation of the degree of axonal injury during the first few months. A 70% decrement in CMAP amplitude correlates to 70% axon loss. Amplitude differences of less than 50% may not be significant.

Question 14

PERIPHERAL NEUROPATHY
Late Response – Most lesions are incomplete and the effect is diluted along the neural path of transmission of the F wave. Therefore, F-wave prolongation is a nonspecific finding and _________ wave and _________-reflexes are usually not helpful in the diagnosis of plexopathies.

Answer 14

PERIPHERAL NEUROPATHY
Late Response – Most lesions are incomplete and the effect is diluted along the neural path of transmission of the F wave. Therefore, F-wave prolongation is a nonspecific finding and F wave and H-reflexes are usually not helpful in the diagnosis of plexopathies.

Question 15

PERIPHERAL NEUROPATHY
EMG – Acute plexopathies usually show fibs and PSWs in the distribution of the nerve segment involved (see Tables 17-5 and 17-6). In chronic lesions where reinnervation has occurred, _________-duration, _________-amplitude, or _________ MUAPs may be noted. It may take up to _________ weeks for electrodiagnostic abnormalities to develop. The paraspinal muscles, as well as muscles not in the distribution of the nerve segment involved, are expected to be normal.

Answer 15

PERIPHERAL NEUROPATHY
EMG – Acute plexopathies usually show fibs and PSWs in the distribution of the nerve segment involved (see Tables 17-5 and 17-6). In chronic lesions where reinnervation has occurred, long-duration, high-amplitude, or polyphasic MUAPs may be noted. It may take up to 3 weeks for electrodiagnostic abnormalities to develop. The paraspinal muscles, as well as muscles not in the distribution of the nerve segment involved, are expected to be normal.

Question 16

RADICULOPATHY
Radiculopathy is a lesion of a specific nerve root that is generally caused by compression of that root. Electrodiagnostic studies aid in the diagnosis of radiculopathy, but they must be done in conjunction with a thorough history and physical examination. Imaging studies may be complementary, but they do not give information about nerve function. Physical examination findings suggestive of radiculopathy can include decreased _________, _________ in myotomal distribution, and/or decreased _________ in a dermatomal distribution. Despite the fact that sensory complaints are common in patients with suspected/diagnosed radiculopathy, the SNAPs will be normal in amplitude and latency as the lesion is proximal to the DRGs. If there are abnormal SNAP findings, a different (or coexisting) lesion distal to the DRG should be considered.

Answer 16

RADICULOPATHY
Radiculopathy is a lesion of a specific nerve root that is generally caused by compression of that root. Electrodiagnostic studies aid in the diagnosis of radiculopathy, but they must be done in conjunction with a thorough history and physical examination. Imaging studies may be complementary, but they do not give information about nerve function. Physical examination findings suggestive of radiculopathy can include decreased reflexes, weakness in myotomal distribution, and/or decreased sensation in a dermatomal distribution. Despite the fact that sensory complaints are common in patients with suspected/diagnosed radiculopathy, the SNAPs will be normal in amplitude and latency as the lesion is proximal to the DRGs. If there are abnormal SNAP findings, a different (or coexisting) lesion distal to the DRG should be considered.

Question 17

RADICULOPATHY
CMAPs reflect the number of motor fibers activated upon stimulation. In most cases, the CMAP will also be normal in a radiculopathy. In a severe, multilevel radiculopathy, the CMAP amplitude may be reduced as a result of _________ degeneration distal to the lesion.

Answer 17

RADICULOPATHY
CMAPs reflect the number of motor fibers activated upon stimulation. In most cases, the CMAP will also be normal in a radiculopathy. In a severe, multilevel radiculopathy, the CMAP amplitude may be reduced as a result of Wallerian degeneration distal to the lesion.

Question 18

RADICULOPATHY
The H-reflex can be used to assess the afferent and efferent S1 fibers and can be helpful in distinguishing an S1 from an L5 radiculopathy. It is important to remember that H-reflexes are sensitive but not specific. Gastrocnemius–soleus H-reflex side-to-side latency differences of greater than _________ m/s are suggestive of S1 radiculopathy (as is unilateral absence of an H-reflex). F-wave latencies and amplitudes are so variable that their use in evaluating a patient for radiculopathy is not recommended.

Answer 18

RADICULOPATHY
The H-reflex can be used to assess the afferent and efferent S1 fibers and can be helpful in distinguishing an S1 from an L5 radiculopathy. It is important to remember that H-reflexes are sensitive but not specific. Gastrocnemius–soleus H-reflex side-to-side latency differences of greater than 1.5 m/s are suggestive of S1 radiculopathy (as is unilateral absence of an H-reflex). F-wave latencies and amplitudes are so variable that their use in evaluating a patient for radiculopathy is not recommended.

Question 19

RADICULOPATHY
Needle EMG is the most useful study in the electrodiagnostic evaluation to both localize a radiculopathy and predict its prognosis. The presence of spontaneous activity on needle EMG is the most objective evidence of _________ denervation. Fibs and PSWs can be seen in the paraspinal muscles within _________ to _________ days of initial injury. This is followed by findings in the peripheral muscles within _________ to _________ weeks. In order to diagnose radiculopathy, the corresponding paraspinal muscle and two peripheral muscles innervated by different peripheral nerves, but the same nerve root, should have positive findings (see Tables 17-7 and 17-8).

Answer 19

RADICULOPATHY
Needle EMG is the most useful study in the electrodiagnostic evaluation to both localize a radiculopathy and predict its prognosis. The presence of spontaneous activity on needle EMG is the most objective evidence of acute denervation. Fibs and PSWs can be seen in the paraspinal muscles within 5 to 7 days of initial injury. This is followed by findings in the peripheral muscles within 3 to 6 weeks. In order to diagnose radiculopathy, the corresponding paraspinal muscle and two peripheral muscles innervated by different peripheral nerves, but the same nerve root, should have positive findings (see Tables 17-7 and 17-8).

Question 20

RADICULOPATHY
With axon loss, MUs will fire with increasing _________ (>20 Hz); this is also known as “_________ recruitment.”

Answer 20

RADICULOPATHY
With axon loss, MUs will fire with increasing frequency (>20 Hz); this is also known as “decreased recruitment.”

Question 21

RADICULOPATHY
With reinnervation, the abnormal spontaneous activity may disappear (in the paraspinals at _________ to _________ weeks followed by proximal muscles at _________ to _________ months and distal muscles at _________ to _________ months). MUAPs will become polyphasic with a long duration (>15 ms). After 6 months to 1 year, _________-amplitude (>7 mV using a monopolar needle) MUAPs may be noted.

Answer 21

RADICULOPATHY
With reinnervation, the abnormal spontaneous activity may disappear (in the paraspinals at 6 to 9 weeks followed by proximal muscles at 2 to 5 months and distal muscles at 3 to 7 months). MUAPs will become polyphasic with a long duration (>15 ms). After 6 months to 1 year, large-amplitude (>7 mV using a monopolar needle) MUAPs may be noted.

Question 22

PERIPHERAL NEUROPATHY
EMG – Acute plexopathies usually show fibs and PSWs in the distribution of the nerve segment involved (see Tables 17-5 and 17-6). In chronic lesions where reinnervation has occurred, _________-duration, _________-amplitude, or _________ MUAPs may be noted. It may take up to _________ weeks for electrodiagnostic abnormalities to develop. The paraspinal muscles, as well as muscles not in the distribution of the nerve segment involved, are expected to be normal.

Answer 22

PERIPHERAL NEUROPATHY
EMG – Acute plexopathies usually show fibs and PSWs in the distribution of the nerve segment involved (see Tables 17-5 and 17-6). In chronic lesions where reinnervation has occurred, long-duration, high-amplitude, or polyphasic MUAPs may be noted. It may take up to 3 weeks for electrodiagnostic abnormalities to develop. The paraspinal muscles, as well as muscles not in the distribution of the nerve segment involved, are expected to be normal.

Question 23

RADICULOPATHY
Radiculopathy is a lesion of a specific nerve root that is generally caused by compression of that root. Electrodiagnostic studies aid in the diagnosis of radiculopathy, but they must be done in conjunction with a thorough history and physical examination. Imaging studies may be complementary, but they do not give information about nerve function. Physical examination findings suggestive of radiculopathy can include decreased _________, _________ in myotomal distribution, and/or decreased _________ in a dermatomal distribution. Despite the fact that sensory complaints are common in patients with suspected/diagnosed radiculopathy, the SNAPs will be normal in amplitude and latency as the lesion is proximal to the DRGs. If there are abnormal SNAP findings, a different (or coexisting) lesion distal to the DRG should be considered.

Answer 23

RADICULOPATHY
Radiculopathy is a lesion of a specific nerve root that is generally caused by compression of that root. Electrodiagnostic studies aid in the diagnosis of radiculopathy, but they must be done in conjunction with a thorough history and physical examination. Imaging studies may be complementary, but they do not give information about nerve function. Physical examination findings suggestive of radiculopathy can include decreased reflexes, weakness in myotomal distribution, and/or decreased sensation in a dermatomal distribution. Despite the fact that sensory complaints are common in patients with suspected/diagnosed radiculopathy, the SNAPs will be normal in amplitude and latency as the lesion is proximal to the DRGs. If there are abnormal SNAP findings, a different (or coexisting) lesion distal to the DRG should be considered.

Question 24

RADICULOPATHY
Radiculopathy is a lesion of a specific nerve root that is generally caused by compression of that root. Electrodiagnostic studies aid in the diagnosis of radiculopathy, but they must be done in conjunction with a thorough history and physical examination. Imaging studies may be complementary, but they do not give information about nerve function. Physical examination findings suggestive of radiculopathy can include decreased _________, _________ in myotomal distribution, and/or decreased _________ in a dermatomal distribution. Despite the fact that sensory complaints are common in patients with suspected/diagnosed radiculopathy, the SNAPs will be normal in amplitude and latency as the lesion is proximal to the DRGs. If there are abnormal SNAP findings, a different (or coexisting) lesion distal to the DRG should be considered.

Answer 24

RADICULOPATHY
Radiculopathy is a lesion of a specific nerve root that is generally caused by compression of that root. Electrodiagnostic studies aid in the diagnosis of radiculopathy, but they must be done in conjunction with a thorough history and physical examination. Imaging studies may be complementary, but they do not give information about nerve function. Physical examination findings suggestive of radiculopathy can include decreased reflexes, weakness in myotomal distribution, and/or decreased sensation in a dermatomal distribution. Despite the fact that sensory complaints are common in patients with suspected/diagnosed radiculopathy, the SNAPs will be normal in amplitude and latency as the lesion is proximal to the DRGs. If there are abnormal SNAP findings, a different (or coexisting) lesion distal to the DRG should be considered.

Question 25

RADICULOPATHY
CMAPs reflect the number of motor fibers activated upon stimulation. In most cases, the CMAP will also be normal in a radiculopathy. In a severe, multilevel radiculopathy, the CMAP amplitude may be reduced as a result of _________ degeneration distal to the lesion.

Answer 25

RADICULOPATHY
CMAPs reflect the number of motor fibers activated upon stimulation. In most cases, the CMAP will also be normal in a radiculopathy. In a severe, multilevel radiculopathy, the CMAP amplitude may be reduced as a result of Wallerian degeneration distal to the lesion.

Question 26

RADICULOPATHY
CMAPs reflect the number of motor fibers activated upon stimulation. In most cases, the CMAP will also be normal in a radiculopathy. In a severe, multilevel radiculopathy, the CMAP amplitude may be reduced as a result of _________ degeneration distal to the lesion.

Answer 26

RADICULOPATHY
CMAPs reflect the number of motor fibers activated upon stimulation. In most cases, the CMAP will also be normal in a radiculopathy. In a severe, multilevel radiculopathy, the CMAP amplitude may be reduced as a result of Wallerian degeneration distal to the lesion.

Question 27

PERIPHERAL NEUROPATHY
Axonal motor neuropathy: affected muscles (usually distal) may demonstrate spontaneous activity (_________ and _________). If an axonal lesion is present, the duration of the disease can be assessed by evaluating chronic changes in MUAPs (increased _________, _________, or large _________ reveals reinnervation and reorganization).

Answer 27

PERIPHERAL NEUROPATHY
Axonal motor neuropathy: affected muscles (usually distal) may demonstrate spontaneous activity (fibs and PSW). If an axonal lesion is present, the duration of the disease can be assessed by evaluating chronic changes in MUAPs (increased duration, polyphasicity, or large amplitude reveals reinnervation and reorganization).

Question 28

PERIPHERAL NEUROPATHY
Axonal motor neuropathy: affected muscles (usually distal) may demonstrate spontaneous activity (_________ and _________). If an axonal lesion is present, the duration of the disease can be assessed by evaluating chronic changes in MUAPs (increased _________, _________, or large _________ reveals reinnervation and reorganization).

Answer 28

PERIPHERAL NEUROPATHY
Axonal motor neuropathy: affected muscles (usually distal) may demonstrate spontaneous activity (fibs and PSW). If an axonal lesion is present, the duration of the disease can be assessed by evaluating chronic changes in MUAPs (increased duration, polyphasicity, or large amplitude reveals reinnervation and reorganization).

Question 29

PERIPHERAL NEUROPATHY
There are many causes for peripheral neuropathy, including _________ and _________ disorders. These disorders are further typified based on separate classifications of peripheral neuropathy that can be derived using electrodiagnostic studies (Table 17-4).

Answer 29

PERIPHERAL NEUROPATHY
There are many causes for peripheral neuropathy, including genetic and acquired disorders. These disorders are further typified based on separate classifications of peripheral neuropathy that can be derived using electrodiagnostic studies (Table 17-4).

Question 30

PERIPHERAL NEUROPATHY
There are many causes for peripheral neuropathy, including _________ and _________ disorders. These disorders are further typified based on separate classifications of peripheral neuropathy that can be derived using electrodiagnostic studies (Table 17-4).

Answer 30

PERIPHERAL NEUROPATHY
There are many causes for peripheral neuropathy, including genetic and acquired disorders. These disorders are further typified based on separate classifications of peripheral neuropathy that can be derived using electrodiagnostic studies (Table 17-4).

Question 31

PERIPHERAL NEUROPATHY
Plexopathy – The functional anatomy of the brachial plexus can be divided into _________ (roots and trunks) and _________ (cords and peripheral nerves or branches) (Fig. 17-7). The pattern of findings will help to localize the lesion. In general, _________ lesions will cause weakness in a muscle group without affecting the antagonist muscles of that group, whereas _________ lesions will affect _________. Electrodiagnostic testing is a physiological examination, which can help to localize the site of a plexus lesion and provide an evaluation of the prognosis. The unaffected limb should be used as a control to compare nerve responses from the two sides tested.

Answer 31

PERIPHERAL NEUROPATHY
Plexopathy – The functional anatomy of the brachial plexus can be divided into supraclavicular (roots and trunks) and infraclavicular (cords and peripheral nerves or branches) (Fig. 17-7). The pattern of findings will help to localize the lesion. In general, infraclavicular lesions will cause weakness in a muscle group without affecting the antagonist muscles of that group, whereas supraclavicular lesions will affect both. Electrodiagnostic testing is a physiological examination, which can help to localize the site of a plexus lesion and provide an evaluation of the prognosis. The unaffected limb should be used as a control to compare nerve responses from the two sides tested.

Question 32

PERIPHERAL NEUROPATHY
Plexopathy – The functional anatomy of the brachial plexus can be divided into _________ (roots and trunks) and _________ (cords and peripheral nerves or branches) (Fig. 17-7). The pattern of findings will help to localize the lesion. In general, _________ lesions will cause weakness in a muscle group without affecting the antagonist muscles of that group, whereas _________ lesions will affect _________. Electrodiagnostic testing is a physiological examination, which can help to localize the site of a plexus lesion and provide an evaluation of the prognosis. The unaffected limb should be used as a control to compare nerve responses from the two sides tested.

Answer 32

PERIPHERAL NEUROPATHY
Plexopathy – The functional anatomy of the brachial plexus can be divided into supraclavicular (roots and trunks) and infraclavicular (cords and peripheral nerves or branches) (Fig. 17-7). The pattern of findings will help to localize the lesion. In general, infraclavicular lesions will cause weakness in a muscle group without affecting the antagonist muscles of that group, whereas supraclavicular lesions will affect both. Electrodiagnostic testing is a physiological examination, which can help to localize the site of a plexus lesion and provide an evaluation of the prognosis. The unaffected limb should be used as a control to compare nerve responses from the two sides tested.

Question 33

PERIPHERAL NEUROPATHY
Sensory Studies – _________ NCSs are usually a more sensitive indicator of injury to the plexus than the motor nerve response. The distal latency and CV are usually normal. _________ amplitude reflects the number of functioning axons in continuity with the sensory root cell body. Lesions proximal to the DRG, such as radiculopathy and nerve root avulsions, have normal SNAPs even though sensation may be affected clinically. Lesions distal to the DRG disconnect the sensory nerve cell body from its axons, resulting in decrement or absence of the SNAP. Therefore, differentiation between pre- and postganglionic lesions is extremely important.

Answer 33

PERIPHERAL NEUROPATHY
Sensory Studies – Sensory NCSs are usually a more sensitive indicator of injury to the plexus than the motor nerve response. The distal latency and CV are usually normal. SNAP amplitude reflects the number of functioning axons in continuity with the sensory root cell body. Lesions proximal to the DRG, such as radiculopathy and nerve root avulsions, have normal SNAPs even though sensation may be affected clinically. Lesions distal to the DRG disconnect the sensory nerve cell body from its axons, resulting in decrement or absence of the SNAP. Therefore, differentiation between pre- and postganglionic lesions is extremely important.

Question 34

PERIPHERAL NEUROPATHY
Sensory Studies – _________ NCSs are usually a more sensitive indicator of injury to the plexus than the motor nerve response. The distal latency and CV are usually normal. _________ amplitude reflects the number of functioning axons in continuity with the sensory root cell body. Lesions proximal to the DRG, such as radiculopathy and nerve root avulsions, have normal SNAPs even though sensation may be affected clinically. Lesions distal to the DRG disconnect the sensory nerve cell body from its axons, resulting in decrement or absence of the SNAP. Therefore, differentiation between pre- and postganglionic lesions is extremely important.

Answer 34

PERIPHERAL NEUROPATHY
Sensory Studies – Sensory NCSs are usually a more sensitive indicator of injury to the plexus than the motor nerve response. The distal latency and CV are usually normal. SNAP amplitude reflects the number of functioning axons in continuity with the sensory root cell body. Lesions proximal to the DRG, such as radiculopathy and nerve root avulsions, have normal SNAPs even though sensation may be affected clinically. Lesions distal to the DRG disconnect the sensory nerve cell body from its axons, resulting in decrement or absence of the SNAP. Therefore, differentiation between pre- and postganglionic lesions is extremely important.

Question 35

PERIPHERAL NEUROPATHY
Motor Studies – CMAPs are usually not affected unless the injury is severe. Motor latencies and conduction velocities are usually unaffected. Stimulation at _________ point may reveal slowing if there is a demyelinating lesion in the brachial plexus. CMAP amplitudes may be decreased if there is severe axonal damage. In plexopathies, side-to-side amplitude differences can give an approximation of the degree of axonal injury during the first few months. A 70% decrement in CMAP amplitude correlates to _________% axon loss. Amplitude differences of less than _________% may not be significant.

Answer 35

PERIPHERAL NEUROPATHY
Motor Studies – CMAPs are usually not affected unless the injury is severe. Motor latencies and conduction velocities are usually unaffected. Stimulation at Erb’s point may reveal slowing if there is a demyelinating lesion in the brachial plexus. CMAP amplitudes may be decreased if there is severe axonal damage. In plexopathies, side-to-side amplitude differences can give an approximation of the degree of axonal injury during the first few months. A 70% decrement in CMAP amplitude correlates to 70% axon loss. Amplitude differences of less than 50% may not be significant.

Question 36

PERIPHERAL NEUROPATHY
Motor Studies – CMAPs are usually not affected unless the injury is severe. Motor latencies and conduction velocities are usually unaffected. Stimulation at _________ point may reveal slowing if there is a demyelinating lesion in the brachial plexus. CMAP amplitudes may be decreased if there is severe axonal damage. In plexopathies, side-to-side amplitude differences can give an approximation of the degree of axonal injury during the first few months. A 70% decrement in CMAP amplitude correlates to _________% axon loss. Amplitude differences of less than _________% may not be significant.

Answer 36

PERIPHERAL NEUROPATHY
Motor Studies – CMAPs are usually not affected unless the injury is severe. Motor latencies and conduction velocities are usually unaffected. Stimulation at Erb’s point may reveal slowing if there is a demyelinating lesion in the brachial plexus. CMAP amplitudes may be decreased if there is severe axonal damage. In plexopathies, side-to-side amplitude differences can give an approximation of the degree of axonal injury during the first few months. A 70% decrement in CMAP amplitude correlates to 70% axon loss. Amplitude differences of less than 50% may not be significant.

Question 37

PERIPHERAL NEUROPATHY
Late Response – Most lesions are incomplete and the effect is diluted along the neural path of transmission of the F wave. Therefore, F-wave prolongation is a nonspecific finding and _________ wave and _________-reflexes are usually not helpful in the diagnosis of plexopathies.

Answer 37

PERIPHERAL NEUROPATHY
Late Response – Most lesions are incomplete and the effect is diluted along the neural path of transmission of the F wave. Therefore, F-wave prolongation is a nonspecific finding and F wave and H-reflexes are usually not helpful in the diagnosis of plexopathies.

Question 38

PERIPHERAL NEUROPATHY
Late Response – Most lesions are incomplete and the effect is diluted along the neural path of transmission of the F wave. Therefore, F-wave prolongation is a nonspecific finding and _________ wave and _________-reflexes are usually not helpful in the diagnosis of plexopathies.

Answer 38

PERIPHERAL NEUROPATHY
Late Response – Most lesions are incomplete and the effect is diluted along the neural path of transmission of the F wave. Therefore, F-wave prolongation is a nonspecific finding and F wave and H-reflexes are usually not helpful in the diagnosis of plexopathies.

Question 39

PERIPHERAL NEUROPATHY
EMG – Acute plexopathies usually show fibs and PSWs in the distribution of the nerve segment involved (see Tables 17-5 and 17-6). In chronic lesions where reinnervation has occurred, _________-duration, _________-amplitude, or _________ MUAPs may be noted. It may take up to _________ weeks for electrodiagnostic abnormalities to develop. The paraspinal muscles, as well as muscles not in the distribution of the nerve segment involved, are expected to be normal.

Answer 39

PERIPHERAL NEUROPATHY
EMG – Acute plexopathies usually show fibs and PSWs in the distribution of the nerve segment involved (see Tables 17-5 and 17-6). In chronic lesions where reinnervation has occurred, long-duration, high-amplitude, or polyphasic MUAPs may be noted. It may take up to 3 weeks for electrodiagnostic abnormalities to develop. The paraspinal muscles, as well as muscles not in the distribution of the nerve segment involved, are expected to be normal.

Question 40

PERIPHERAL NEUROPATHY
EMG – Acute plexopathies usually show fibs and PSWs in the distribution of the nerve segment involved (see Tables 17-5 and 17-6). In chronic lesions where reinnervation has occurred, _________-duration, _________-amplitude, or _________ MUAPs may be noted. It may take up to _________ weeks for electrodiagnostic abnormalities to develop. The paraspinal muscles, as well as muscles not in the distribution of the nerve segment involved, are expected to be normal.

Answer 40

PERIPHERAL NEUROPATHY
EMG – Acute plexopathies usually show fibs and PSWs in the distribution of the nerve segment involved (see Tables 17-5 and 17-6). In chronic lesions where reinnervation has occurred, long-duration, high-amplitude, or polyphasic MUAPs may be noted. It may take up to 3 weeks for electrodiagnostic abnormalities to develop. The paraspinal muscles, as well as muscles not in the distribution of the nerve segment involved, are expected to be normal.

Question 41

RADICULOPATHY
Radiculopathy is a lesion of a specific nerve root that is generally caused by compression of that root. Electrodiagnostic studies aid in the diagnosis of radiculopathy, but they must be done in conjunction with a thorough history and physical examination. Imaging studies may be complementary, but they do not give information about nerve function. Physical examination findings suggestive of radiculopathy can include decreased _________, _________ in myotomal distribution, and/or decreased _________ in a dermatomal distribution. Despite the fact that sensory complaints are common in patients with suspected/diagnosed radiculopathy, the SNAPs will be normal in amplitude and latency as the lesion is proximal to the DRGs. If there are abnormal SNAP findings, a different (or coexisting) lesion distal to the DRG should be considered.

Answer 41

RADICULOPATHY
Radiculopathy is a lesion of a specific nerve root that is generally caused by compression of that root. Electrodiagnostic studies aid in the diagnosis of radiculopathy, but they must be done in conjunction with a thorough history and physical examination. Imaging studies may be complementary, but they do not give information about nerve function. Physical examination findings suggestive of radiculopathy can include decreased reflexes, weakness in myotomal distribution, and/or decreased sensation in a dermatomal distribution. Despite the fact that sensory complaints are common in patients with suspected/diagnosed radiculopathy, the SNAPs will be normal in amplitude and latency as the lesion is proximal to the DRGs. If there are abnormal SNAP findings, a different (or coexisting) lesion distal to the DRG should be considered.

Question 42

RADICULOPATHY
Radiculopathy is a lesion of a specific nerve root that is generally caused by compression of that root. Electrodiagnostic studies aid in the diagnosis of radiculopathy, but they must be done in conjunction with a thorough history and physical examination. Imaging studies may be complementary, but they do not give information about nerve function. Physical examination findings suggestive of radiculopathy can include decreased _________, _________ in myotomal distribution, and/or decreased _________ in a dermatomal distribution. Despite the fact that sensory complaints are common in patients with suspected/diagnosed radiculopathy, the SNAPs will be normal in amplitude and latency as the lesion is proximal to the DRGs. If there are abnormal SNAP findings, a different (or coexisting) lesion distal to the DRG should be considered.

Answer 42

RADICULOPATHY
Radiculopathy is a lesion of a specific nerve root that is generally caused by compression of that root. Electrodiagnostic studies aid in the diagnosis of radiculopathy, but they must be done in conjunction with a thorough history and physical examination. Imaging studies may be complementary, but they do not give information about nerve function. Physical examination findings suggestive of radiculopathy can include decreased reflexes, weakness in myotomal distribution, and/or decreased sensation in a dermatomal distribution. Despite the fact that sensory complaints are common in patients with suspected/diagnosed radiculopathy, the SNAPs will be normal in amplitude and latency as the lesion is proximal to the DRGs. If there are abnormal SNAP findings, a different (or coexisting) lesion distal to the DRG should be considered.

Question 43

RADICULOPATHY
CMAPs reflect the number of motor fibers activated upon stimulation. In most cases, the CMAP will also be normal in a radiculopathy. In a severe, multilevel radiculopathy, the CMAP amplitude may be reduced as a result of _________ degeneration distal to the lesion.

Answer 43

RADICULOPATHY
CMAPs reflect the number of motor fibers activated upon stimulation. In most cases, the CMAP will also be normal in a radiculopathy. In a severe, multilevel radiculopathy, the CMAP amplitude may be reduced as a result of Wallerian degeneration distal to the lesion.

Question 44

RADICULOPATHY
CMAPs reflect the number of motor fibers activated upon stimulation. In most cases, the CMAP will also be normal in a radiculopathy. In a severe, multilevel radiculopathy, the CMAP amplitude may be reduced as a result of _________ degeneration distal to the lesion.

Answer 44

RADICULOPATHY
CMAPs reflect the number of motor fibers activated upon stimulation. In most cases, the CMAP will also be normal in a radiculopathy. In a severe, multilevel radiculopathy, the CMAP amplitude may be reduced as a result of Wallerian degeneration distal to the lesion.

Question 45

RADICULOPATHY
The H-reflex can be used to assess the afferent and efferent S1 fibers and can be helpful in distinguishing an S1 from an L5 radiculopathy. It is important to remember that H-reflexes are sensitive but not specific. Gastrocnemius–soleus H-reflex side-to-side latency differences of greater than _________ m/s are suggestive of S1 radiculopathy (as is unilateral absence of an H-reflex). F-wave latencies and amplitudes are so variable that their use in evaluating a patient for radiculopathy is not recommended.

Answer 45

RADICULOPATHY
The H-reflex can be used to assess the afferent and efferent S1 fibers and can be helpful in distinguishing an S1 from an L5 radiculopathy. It is important to remember that H-reflexes are sensitive but not specific. Gastrocnemius–soleus H-reflex side-to-side latency differences of greater than 1.5 m/s are suggestive of S1 radiculopathy (as is unilateral absence of an H-reflex). F-wave latencies and amplitudes are so variable that their use in evaluating a patient for radiculopathy is not recommended.

Question 46

RADICULOPATHY
Needle EMG is the most useful study in the electrodiagnostic evaluation to both localize a radiculopathy and predict its prognosis. The presence of spontaneous activity on needle EMG is the most objective evidence of _________ denervation. Fibs and PSWs can be seen in the paraspinal muscles within _________ to _________ days of initial injury. This is followed by findings in the peripheral muscles within _________ to _________ weeks. In order to diagnose radiculopathy, the corresponding paraspinal muscle and two peripheral muscles innervated by different peripheral nerves, but the same nerve root, should have positive findings (see Tables 17-7 and 17-8).

Answer 46

RADICULOPATHY
Needle EMG is the most useful study in the electrodiagnostic evaluation to both localize a radiculopathy and predict its prognosis. The presence of spontaneous activity on needle EMG is the most objective evidence of acute denervation. Fibs and PSWs can be seen in the paraspinal muscles within 5 to 7 days of initial injury. This is followed by findings in the peripheral muscles within 3 to 6 weeks. In order to diagnose radiculopathy, the corresponding paraspinal muscle and two peripheral muscles innervated by different peripheral nerves, but the same nerve root, should have positive findings (see Tables 17-7 and 17-8).

Question 47

RADICULOPATHY
With axon loss, MUs will fire with increasing _________ (>20 Hz); this is also known as “_________ recruitment.”

Answer 47

RADICULOPATHY
With axon loss, MUs will fire with increasing frequency (>20 Hz); this is also known as “decreased recruitment.”

Question 48

RADICULOPATHY
With reinnervation, the abnormal spontaneous activity may disappear (in the paraspinals at _________ to _________ weeks followed by proximal muscles at _________ to _________ months and distal muscles at _________ to _________ months). MUAPs will become polyphasic with a long duration (>15 ms). After 6 months to 1 year, _________-amplitude (>7 mV using a monopolar needle) MUAPs may be noted.

Answer 48

RADICULOPATHY
With reinnervation, the abnormal spontaneous activity may disappear (in the paraspinals at 6 to 9 weeks followed by proximal muscles at 2 to 5 months and distal muscles at 3 to 7 months). MUAPs will become polyphasic with a long duration (>15 ms). After 6 months to 1 year, large-amplitude (>7 mV using a monopolar needle) MUAPs may be noted.

Question 49

RADICULOPATHY
With reinnervation, the abnormal spontaneous activity may disappear (in the paraspinals at _________ to _________ weeks followed by proximal muscles at _________ to _________ months and distal muscles at _________ to _________ months). MUAPs will become polyphasic with a long duration (>15 ms). After 6 months to 1 year, _________-amplitude (>7 mV using a monopolar needle) MUAPs may be noted.

Answer 49

RADICULOPATHY
With reinnervation, the abnormal spontaneous activity may disappear (in the paraspinals at 6 to 9 weeks followed by proximal muscles at 2 to 5 months and distal muscles at 3 to 7 months). MUAPs will become polyphasic with a long duration (>15 ms). After 6 months to 1 year, large-amplitude (>7 mV using a monopolar needle) MUAPs may be noted.

Question 50

RADICULOPATHY
With reinnervation, the abnormal spontaneous activity may disappear (in the paraspinals at _________ to _________ weeks followed by proximal muscles at _________ to _________ months and distal muscles at _________ to _________ months). MUAPs will become polyphasic with a long duration (>15 ms). After 6 months to 1 year, _________-amplitude (>7 mV using a monopolar needle) MUAPs may be noted.

Answer 50

RADICULOPATHY
With reinnervation, the abnormal spontaneous activity may disappear (in the paraspinals at 6 to 9 weeks followed by proximal muscles at 2 to 5 months and distal muscles at 3 to 7 months). MUAPs will become polyphasic with a long duration (>15 ms). After 6 months to 1 year, large-amplitude (>7 mV using a monopolar needle) MUAPs may be noted.

Question 51

RADICULOPATHY
With reinnervation, the abnormal spontaneous activity may disappear (in the paraspinals at _________ to _________ weeks followed by proximal muscles at _________ to _________ months and distal muscles at _________ to _________ months). MUAPs will become polyphasic with a long duration (>15 ms). After 6 months to 1 year, _________-amplitude (>7 mV using a monopolar needle) MUAPs may be noted.

Answer 51

RADICULOPATHY
With reinnervation, the abnormal spontaneous activity may disappear (in the paraspinals at 6 to 9 weeks followed by proximal muscles at 2 to 5 months and distal muscles at 3 to 7 months). MUAPs will become polyphasic with a long duration (>15 ms). After 6 months to 1 year, large-amplitude (>7 mV using a monopolar needle) MUAPs may be noted.

Question 52

RADICULOPATHY
With reinnervation, the abnormal spontaneous activity may disappear (in the paraspinals at _________ to _________ weeks followed by proximal muscles at _________ to _________ months and distal muscles at _________ to _________ months). MUAPs will become polyphasic with a long duration (>15 ms). After 6 months to 1 year, _________-amplitude (>7 mV using a monopolar needle) MUAPs may be noted.

Answer 52

RADICULOPATHY
With reinnervation, the abnormal spontaneous activity may disappear (in the paraspinals at 6 to 9 weeks followed by proximal muscles at 2 to 5 months and distal muscles at 3 to 7 months). MUAPs will become polyphasic with a long duration (>15 ms). After 6 months to 1 year, large-amplitude (>7 mV using a monopolar needle) MUAPs may be noted.

Question 53

MOTOR NEURON DISEASES
Motor neuron diseases may affect both the UMNs and lower motor neurons (LMNs). These disorders specifically affect the motor cortex, corticospinal tracts, and/or anterior horn cells. Clinical signs of LMN lesions include _________, _________, _________, and fasciculations. UMN signs include weakness, spasticity, hyperreflexia, and upgoing plantar reflex (positive Babinski sign). There are usually no sensory changes. With EMG testing, only the LMN aspect of the disorder can be assessed.

Answer 53

MOTOR NEURON DISEASES
Motor neuron diseases may affect both the UMNs and lower motor neurons (LMNs). These disorders specifically affect the motor cortex, corticospinal tracts, and/or anterior horn cells. Clinical signs of LMN lesions include atrophy, flaccidity, hyporeflexia, and fasciculations. UMN signs include weakness, spasticity, hyperreflexia, and upgoing plantar reflex (positive Babinski sign). There are usually no sensory changes. With EMG testing, only the LMN aspect of the disorder can be assessed.

Question 54

MOTOR NEURON DISEASES
Electrodiagnostic Findings – SNAP has _________ amplitude and conduction velocities. CMAP conduction velocities are _________ or mildly decreased. The amplitude of the CMAP may be decreased due to axonal loss if significant atrophy is present. EMG findings (in at least three limbs or two limbs and bulbar muscles) include abnormal spontaneous potentials (fibs and PSW), fasciculations, and CRDs. Decreased recruitment with increased firing frequency may be noted. Large-amplitude, long-duration polyphasic potentials may be noted if reinnervation has occurred.

Answer 54

MOTOR NEURON DISEASES
Electrodiagnostic Findings – SNAP has normal amplitude and conduction velocities. CMAP conduction velocities are normal or mildly decreased. The amplitude of the CMAP may be decreased due to axonal loss if significant atrophy is present. EMG findings (in at least three limbs or two limbs and bulbar muscles) include abnormal spontaneous potentials (fibs and PSW), fasciculations, and CRDs. Decreased recruitment with increased firing frequency may be noted. Large-amplitude, long-duration polyphasic potentials may be noted if reinnervation has occurred.

Question 55

MOTOR NEURON DISEASES
LMN: _________/_________ syndrome (_________) and _________ _________ _________.
UMN and LMN: _________ _________ _________ (_________).
UMN: _________ _________ _________ (_________).

Answer 55

MOTOR NEURON DISEASES
LMN: Poliomyelitis/postpolio syndrome (PPS) and SMA (Spinal muscular atrophy).
UMN and LMN: Amyotrophic lateral sclerosis (ALS).
UMN: Primary lateral sclerosis (PLS).

Question 56

ALS – Characterized by degeneration of anterior horn cell. _________ and _________ signs are usually present. Clinical presentation includes _________ atrophy, weakness and fasciculations, dysphagia, and dysarthria. _________ signs may be noted. Bowel and bladder are typically _________. EMG findings include abnormal spontaneous potentials (fibs and PSWs). MUAPs demonstrate decreased recruitment with increased MUAP duration and amplitude.

Answer 56

ALS – Characterized by degeneration of anterior horn cell. UMN and LMN signs are usually present. Clinical presentation includes asymmetric atrophy, weakness and fasciculations, dysphagia, and dysarthria. Pseudobulbar signs may be noted. Bowel and bladder are typically spared. EMG findings include abnormal spontaneous potentials (fibs and PSWs). MUAPs demonstrate decreased recruitment with increased MUAP duration and amplitude.

Question 57

PPS – Loss of anterior horn cell decades (typically _________ years) after polio. This disorder is hypothesized to be due to burnout of MU from increased metabolic demand or normal axon loss with aging. _________-_________ criteria include the onset of two or more of the following: _________, _________, _________, and cold intolerance with history of previous stable polio diagnosis. Electrodiagnostically, this may resemble poliomyelitis, so clinical findings must be considered. NCSs show normal SNAPs and abnormal CMAP. EMG shows increased amplitude and duration of MUAPs with decreased recruitment.

Answer 57

PPS – Loss of anterior horn cell decades (typically 30 years) after polio. This disorder is hypothesized to be due to burnout of MU from increased metabolic demand or normal axon loss with aging. Halstead-Ross criteria include the onset of two or more of the following: fatigue, arthralgia, myalgia, and cold intolerance with history of previous stable polio diagnosis. Electrodiagnostically, this may resemble poliomyelitis, so clinical findings must be considered. NCSs show normal SNAPs and abnormal CMAP. EMG shows increased amplitude and duration of MUAPs with decreased recruitment.

Question 58

EMG FINDINGS IN MYOPATHIES
Electrodiagnostic testing is an important tool in the diagnosis of myopathies. EMG testing helps to make a diagnosis, determine the extent of a disease, prognosticate, and guide further studies, such as muscle biopsies. Generally, only one side of the body is tested on EMG, leaving the muscles on the other side preserved for _________ _________. It is important to rule out other diseases by performing at least one sensory and one motor nerve study in addition to the EMG study.

Answer 58

EMG FINDINGS IN MYOPATHIES
Electrodiagnostic testing is an important tool in the diagnosis of myopathies. EMG testing helps to make a diagnosis, determine the extent of a disease, prognosticate, and guide further studies, such as muscle biopsies. Generally, only one side of the body is tested on EMG, leaving the muscles on the other side preserved for muscle biopsy. It is important to rule out other diseases by performing at least one sensory and one motor nerve study in addition to the EMG study.

Question 59

MYOPATHIES Typical Findings
NCS: Usually _________ since myopathies typically affect _________ muscles initially (and in nerve studies, the active electrode is usually placed over a distal muscle). As the disease progresses, _________ muscles may become involved and the motor NCS may be abnormal.
SNAP: _________ (sensory fibers are not affected).
CMAP: amplitudes may be _________ due to muscle fiber atrophy; distal latency and CV are normal as the myelin is not affected.
EMG – MUs will usually show _________ recruitment, _________ (due to the variability in muscle fiber diameter), and small-amplitude (due to muscle fiber dropout) and _________-duration potentials (see Fig. 17-8). Fib potentials and PSWs as well as myotonic discharges can be seen. In long-standing myopathies, there may be little activity at rest due to loss of muscle fiber. Increased insertional activity is also common in many myopathies.

Answer 59

MYOPATHIES Typical Findings
NCS: Usually normal since myopathies typically affect proximal muscles initially (and in nerve studies, the active electrode is usually placed over a distal muscle). As the disease progresses, distal muscles may become involved and the motor NCS may be abnormal.
SNAP: normal (sensory fibers are not affected).
CMAP: amplitudes may be reduced due to muscle fiber atrophy; distal latency and CV are normal as the myelin is not affected.
EMG – MUs will usually show early recruitment, polyphasia (due to the variability in muscle fiber diameter), and small-amplitude (due to muscle fiber dropout) and short-duration potentials (see Fig. 17-8). Fib potentials and PSWs as well as myotonic discharges can be seen. In long-standing myopathies, there may be little activity at rest due to loss of muscle fiber. Increased insertional activity is also common in many myopathies.

Question 60

MYOPATHIES
Typically in myopathies, the proximal lower extremity muscles will show more positive EMG findings. It is important to sample a sufficient number of muscles to differentiate between a myopathy and a focal injury. Muscles should be sampled based on weakness as seen in the clinical examination. However, muscles that are extremely weak (

Answer 60

MYOPATHIES
Typically in myopathies, the proximal lower extremity muscles will show more positive EMG findings. It is important to sample a sufficient number of muscles to differentiate between a myopathy and a focal injury. Muscles should be sampled based on weakness as seen in the clinical examination. However, muscles that are extremely weak (

Question 61

NMJ DISORDERS
The NMJ is divided into the _________ terminal, the _________ cleft, and a _________ muscle end plate. Neuromuscular transmission involves (1) presynaptic terminal depolarization and ACh release, (2) ACh binding and ion channel opening, and (3) postsynaptic membrane depolarization and muscle AP generation. Disorders of the NMJ hinder the production, release, or uptake of ACh at the NMJ. The most well-known postsynaptic disorder is myasthenia gravis (MG). Presynaptic abnormalities include _________-_________ myasthenic syndrome (_________) and _________. A repetitive nerve stimulation (RNS) study and SFEMG are useful electrodiagnostic tests when trying to evaluate for NMJ disorders.

Answer 61

NMJ DISORDERS
The NMJ is divided into the presynaptic terminal, the synaptic cleft, and a postsynaptic muscle end plate. Neuromuscular transmission involves (1) presynaptic terminal depolarization and ACh release, (2) ACh binding and ion channel opening, and (3) postsynaptic membrane depolarization and muscle AP generation. Disorders of the NMJ hinder the production, release, or uptake of ACh at the NMJ. The most well-known postsynaptic disorder is myasthenia gravis (MG). Presynaptic abnormalities include Lambert-Eaton myasthenic syndrome (LEMS) and botulism. A repetitive nerve stimulation (RNS) study and SFEMG are useful electrodiagnostic tests when trying to evaluate for NMJ disorders.

Question 62

NMJ DISORDERS
Routine sensory and motor conduction studies will usually be normal. Only in profound weakness, as in _________ crisis, will borderline or slightly decreased CMAP amplitudes be observed. Routine EMG examination may demonstrate _________ MUAPs, where moment-to-moment variations in amplitude and configuration may be seen.

Answer 62

NMJ DISORDERS
Routine sensory and motor conduction studies will usually be normal. Only in profound weakness, as in myasthenic crisis, will borderline or slightly decreased CMAP amplitudes be observed. Routine EMG examination may demonstrate unstable MUAPs, where moment-to-moment variations in amplitude and configuration may be seen.

Question 63

NMJ DISORDERS
RNS after routine NCS is performed by delivering trains of _________-maximal stimuli to a peripheral nerve while recording CMAPs. This depletes stores of releasable ACh from diseased NMJs, producing a progressive amplitude decrement from the first to the fifth waveform in patients with disorders of the NMJ. When RNS is performed at low rates (_________ to _________ Hz), a decrement of > _________% is considered abnormal. Although the proximal muscles are usually more affected than the distal muscles, the proximal muscles are more difficult to test (the limb must be restrained as the entire limb is often stimulated with proximal stimulation) (Fig. 17-9).

Answer 63

NMJ DISORDERS
RNS after routine NCS is performed by delivering trains of supra-maximal stimuli to a peripheral nerve while recording CMAPs. This depletes stores of releasable ACh from diseased NMJs, producing a progressive amplitude decrement from the first to the fifth waveform in patients with disorders of the NMJ. When RNS is performed at low rates (2 to 5 Hz), a decrement of >10% is considered abnormal. Although the proximal muscles are usually more affected than the distal muscles, the proximal muscles are more difficult to test (the limb must be restrained as the entire limb is often stimulated with proximal stimulation) (Fig. 17-9).

Question 64

NMJ DISORDERS
Postactivation facilitation occurs when there is recovery of the CMAP amplitudes on repeat slow RNS following a _________-second isometric contraction or rapid RNS (_________ to _________ Hz) studies. This is due to calcium facilitation. Although present to a lesser degree in MG and botulism, it is a hallmark finding in LEMS where increments as high as 500% may be observed.

Answer 64

NMJ DISORDERS
Postactivation facilitation occurs when there is recovery of the CMAP amplitudes on repeat slow RNS following a 10-second isometric contraction or rapid RNS (20 to 50 Hz) studies. This is due to calcium facilitation. Although present to a lesser degree in MG and botulism, it is a hallmark finding in LEMS where increments as high as 500% may be observed.

Question 65

NMJ DISORDERS
If initial studies are unrevealing and suspicion for an NMJ disorder is high, consider testing more proximal muscles (e.g., spinal accessory and facial n.) and/or proceeding to SFEMG of at least one symptomatic muscle. SFEMG is the most sensitive test for NMJ disorders. Findings consistent with, but not specific for, NMJ disorders include increased jitter. Jitter refers to _________ variations between _________ discharges of two different muscle fibers of the _________ MU. The most extreme abnormality of jitter is failed transmission, or blocking. In MG, jitter and blocking increase with increased firing rate. In LEMS and botulism, jitter and blocking decrease with increased firing rate (Fig. 17-10).

Answer 65

NMJ DISORDERS
If initial studies are unrevealing and suspicion for an NMJ disorder is high, consider testing more proximal muscles (e.g., spinal accessory and facial n.) and/or proceeding to SFEMG of at least one symptomatic muscle. SFEMG is the most sensitive test for NMJ disorders. Findings consistent with, but not specific for, NMJ disorders include increased jitter. Jitter refers to time variations between interpotential discharges of two different muscle fibers of the same MU. The most extreme abnormality of jitter is failed transmission, or blocking. In MG, jitter and blocking increase with increased firing rate. In LEMS and botulism, jitter and blocking decrease with increased firing rate (Fig. 17-10).

Question 66

NMJ DISORDERS
Prerequisites for performing a reliable RNS study include immobilization of the limb and recording electrode, _________ stimulation, optimization of limb temperature (≈30° C), and withholding of acetylcholinesterase inhibitors 12 to 24 hours prior to testing (if not medically contraindicated). Distal nerves that can be easily tested for RNS are the median and ulnar nerves, with recording electrodes at _________ and _________, respectively. If proximal studies are indicated, spinal accessory nerve with the recording electrode on the upper trapezius muscle is commonly utilized. In patients suspected of having ocular MG, facial RNS recording at orbicularis oris can be performed (Tables 17-9A–E).

Answer 66

NMJ DISORDERS
Prerequisites for performing a reliable RNS study include immobilization of the limb and recording electrode, supramaximal stimulation, optimization of limb temperature (≈30° C), and withholding of acetylcholinesterase inhibitors 12 to 24 hours prior to testing (if not medically contraindicated). Distal nerves that can be easily tested for RNS are the median and ulnar nerves, with recording electrodes at APB and ADM, respectively. If proximal studies are indicated, spinal accessory nerve with the recording electrode on the upper trapezius muscle is commonly utilized. In patients suspected of having ocular MG, facial RNS recording at orbicularis oris can be performed (Tables 17-9A–E).