Electrodiagnosis Flashcards
Myotonic discharges produce a distinctive sound on electromyography (EMG). This sound results
from
(a) spontaneous firing of motor unit action potentials (MUAPs).
(b) intermittent blocking of muscle fibers during voluntary activity.
(c) firing of just a few muscle fibers per motor unit during voluntary activity.
(d) spontaneous firing of muscle fibers
Answer: (d)
Commentary: The classic myotonic discharge of waxing and waning in frequency and amplitude is often described as either a dive-bomber or revving engine. The source generator of a myotonic potential is muscle fiber, and thus may take the form of either positive wave or a brief spike potential. Neuromyotonia and myokymia result in spontaneous firing of motor unit action potentials as opposed to muscle fiber action potentials. Intermittent blocking of some muscle fibers within a motor unit result in unstable MUAPs, which are characterized by changes in either amplitude or number of phases from potential to potential. Unstable MUAPs are seen in primary neuromuscular junction (NMJ) disorders or with new and immature NMJs, as can be seen in early reinnervation. Mypopathic MUAPs result from a decreased number of muscle fibers firing within a motor unit. These signals are seen as short-duration, small amplitude, and polyphasic potentials.
2013
One advantage of a concentric needle compared to a monopolar needle is its
(a) higher amplitude of motor unit action potentials(MUAPS).
(b) decreased likelihood of electrical interference.
(c) ability to vary the recording surface size.
(d) longer duration of the MUAPs.
Answer: (b)
Commentary: The shaft of a concentric needle serves as the reference electrode, whereas an additional electrode (typically a surface electrode) is needed as a reference when using a
monopolar needle. MUAPs recorded from monopolar needles are slightly longer in duration and have higher amplitude, since they record from the entire area around the needle tip rather than only from the fibers facing the bevel. Because the concentric needle shaft serves as the reference electrode, the recording surface size is fixed and interference from surrounding muscles is minimized.
2012
Which type of study best differentiates a severe polyradiculopathy from amyotrophic lateral
sclerosis (ALS)?
(a) Motor nerve conduction studies of upper and lower extremities
(b) Needle electromyography of thoracic paraspinals or bulbar muscles
(c) Sensory nerve conduction studies of upper and lower extremities
(d) Needle electromyography of multiple extremities
Answer (b)
Commentary: Sensory nerve conduction studies are normal in both radiculopathy and motor
neuron disease. Motor nerve conduction studies are also often normal in both diseases. Both
diseases may demonstrate abnormal needle examination in multiple extremities. Thoracic
paraspinals and bulbar muscle examinations are most helpful in differentiating severe
polyradiculopathy from amyotrophic lateral sclerosis (ALS), since one would expect these studies
to be normal in radiculopathy but may be abnormal in ALS
2011
In a patient with a neuromuscular junction disorder, which electrodiagnostic results for compound
muscle action potential (CMAP), motor unit action potential (MUAP) or nerve action potential
(SNAP) may be misleading if the limb is cold?
(a) Diminished CMAP decrement on repetitive nerve stimulation
(b) Diminished polyphasia of the MUAP
(c) Shortened distal latency of the CMAP
(d) Decreased amplitude of the SNAP
Answer (a)
Commentary: In neuromuscular junction (NMJ) disorders, compound muscle action potential
(CMAP) decrement may be diminished if the limb is cold, likely due to decreased functioning of
acetylcholinesterase. Cool temperatures may alter results by slowing nerve conduction velocity,
prolonging distal latency, increasing amplitude and duration of sensory nerve action potential
(SNAP) and CMAP and motor unit action potential (MUAP), increasing phases of MUAP.
2011
A 55-year-old overweight man presents to clinic with complaints of numbness in his left leg. He
reports that he does not exercise and has an office job. He is diagnosed with meralgia
paresthetica. Which of the following is consistent with this diagnosis?
a) Peroneal motor F-wave study is abnormal.
b) Sensory nerve conduction studies reveal decreased amplitude on the affected side.
c) Electromyography findings show denervation in the vastus lateralis.
d) Exam reveals decreased sensation in the medial thigh.
Answer: (b)
Commentary:
Meralgia paresthetica presents with paresthesias in the lateral thigh. Sensory nerve conduction
studies of the lateral femoral cutaneous nerve may show a drop in the sensory nerve action
potential (SNAP) amplitude on the affected side compared to the asymptomatic, contralateral
study. Symptoms are confined to below the inguinal ligament and above the knee. Peroneal motor
nerve conduction studies and F waves should be normal and needle electromyography should not
show acute or chronic axonal motor loss, because the lateral femoral cutaneous nerve is purely
sensory
2011
Myotonic discharges produce a distinctive sound on electromyography (EMG). This sound results from
(a) spontaneous firing of motor unit action potentials (MUAPs).
(b) intermittent blocking of muscle fibers during voluntary activity.
(c) firing of just a few muscle fibers per motor unit during voluntary activity.
(d) spontaneous firing of muscle fibers.
Answer: (d)
Commentary: The classic myotonic discharge of waxing and waning in frequency and amplitude is often described as either a dive-bomber or revving engine. The source generator of a myotonic potential is muscle fiber, and thus may take the form of either positive wave or a brief spike potential. Neuromyotonia and myokymia result in spontaneous firing of motor unit action potentials as opposed to muscle fiber action potentials. Intermittent blocking of some muscle fibers within a motor unit result in unstable MUAPs, which are characterized by changes in either amplitude or number of phases from potential to potential. Unstable MUAPs are seen in primary neuromuscular junction (NMJ) disorders or with new and immature NMJs, as can be seen in early reinnervation. Mypopathic MUAPs result from a decreased number of muscle fibers firing within a motor unit. These signals are seen as short-duration, small amplitude, and polyphasic potentials
2013
Which safety practice is the most appropriate when performing an electrodiagnostic study on a
patient in a hospital bed?
(a) The device should be turned on after the placement of electrodes on the patient.
(b) An insulated extension cord should be used to connect the power line.
(c) More than 1 ground electrode should be attached to the patient.
(d) All electrical devices in contact with the patient should share a common ground
Answer: (d)
Commentary: It is important to have all the electrical devices that are in contact with the patient
plugged into the same outlet to share a common ground. Similarly, only 1 ground electrode
should be used on the patient. To avoid power surges, the device should be turned on prior to the
application of any electrodes to the patient and turned off after the removal of electrodes.
Extension cords can increase leakage currents and should be avoided.
2010
Which characteristic best describes fasciculation potentials?
(a) Semirhythmic in their firing pattern
(b) Morphologically the same as motor unit potentials
(c) Produced by ephaptic conduction between single muscle fibers
(d) Randomly firing single muscle fibers
Answer: (b)
Commentary: Fasciculation potentials are spontaneously firing motor unit potentials with the
same morphologic characteristics as that of a motor unit or polyphasic action potential. They
have an irregular firing pattern usually and the site of origin is unclear. Ephaptic conduction
between single muscle fibers is thought to be the mechanism for complex repetitive discharges.
Single muscle fiber potentials are much smaller and represent units such as a fibrillation potential.
2010
A 37-year-old man is sent to you for electrodiagnostic assessment for right lumbosacral
radiculopathy. Nerve conduction studies of the right leg are normal. Needle exam shows the
following:
NEEDLE ELECTROMYOGRAPHY
Muscle -- Abnormal Spontaneous Activity -- Recruitment Adductor longus 0 Normal Vastus medialis 0 Normal Tensor fascia lata 1+ Normal Semimembranosus 1+ Normal Biceps femoris (short head) 0 Normal Tibialis anterior 2+ Reduced Medial gastrocnemius 0 Normal Lumbar paraspinals 1+
Which root is most likely injured?
(a) L2
(b) L3
(c) L4
(d) L5
Answer: D
Commentary: The common root among the affected muscles is L5. It is often difficult to narrow
the involvement to a single root level.
2010
One advantage of a concentric needle compared to a monopolar needle is its
(a) higher amplitude of motor unit action potentials(MUAPS).
(b) decreased likelihood of electrical interference.
(c) ability to vary the recording surface size.
(d) longer duration of the MUAPs.
Answer: (b)
Commentary: The shaft of a concentric needle serves as the reference electrode, whereas an
additional electrode (typically a surface electrode) is needed as a reference when using a
monopolar needle. MUAPs recorded from monopolar needles are slightly longer in duration and
have higher amplitude, since they record from the entire area around the needle tip rather than
only from the fibers facing the bevel. Because the concentric needle shaft serves as the reference
electrode, the recording surface size is fixed and interference from surrounding muscles is
minimized.
2012
In patients with steroid myopathy, the needle electromyographic study usually reveals
(a) small motor unit action potentials (MUAPs) with early recruitment.
(b) small MUAPs with reduced recruitment.
(c) positive waves and fibrillation potentials in proximal muscles.
(d) normal MUAPs and normal recruitment.
Answer: (d)
Commentary: Needle examination in patients with steroid myopathy usually reveals normal
insertional activity and no abnormal spontaneous activity. Motor unit potential morphology and
recruitment do not reveal any abnormalities. This combination occurs because in steroid
myopathy the type 2 muscle fibers are preferentially affected, in contrast to the first-recruited
type 1 fibers.
2012
- Which finding would you expect in a 35-year-old man with type 1 hereditary motor sensory
neuropathy?
(a) Absence of ankle reflexes
(b) Pes planus
(c) Motor nerve conduction velocity slowing, with evidence of temporal dispersion
(d) Absence of electromyographic spontaneous activity
Answer: (a)
Commentary: Hereditary motor sensory polyneuropathy type 1 (HMSN-1, the demyelinating
form of Charcot-Marie-Tooth disease) presents in young adult life with insidious onset of distal
weakness and sensory loss. Clinically, it typically presents with pes cavus, hammertoes and foot
drop. Ankle reflexes are absent. Temporal dispersion would indicate an acquired, not hereditary,
process. Secondary axonal loss is expected, which would result in positive waves and
fibrillations.
2012
Cooling can produce physiological changes in the body. One of these changes is an increase in
(a) nerve conduction rate.
(b) stretch receptor sensitivity.
(c) elasticity of connective tissue.
(d) general sympathetic activity.
Answer: (d)
Commentary: Nerve conduction rate is slowed by cooling. The stretch receptor sensitivity in
muscles and tendons is reduced, and the elasticity of connective tissue diminishes with cooling.
The general sympathetic activity is increased with cooling of the body, and this may affect the
responses of the stretch receptors in a beneficial way.
2012
A 33-year-old woman who had a prolonged labor 6 weeks ago, reports pain in the groin radiating
along the medial aspect of the thigh. Needle electromyographic exam shows evidence of
denervation in the gracilis and adductor muscles. Most likely she has a lesion in the
(a) femoral nerve.
(b) obturator nerve.
(c) sciatic nerve.
(d) genitofemoral nerve.
Answer: (b)
Commentary: The nerve common to the affected muscles is the obturator nerve. There is some
innervation of the adductor magnus by a branch off the sciatic nerve, but the gracilis, adductor
brevis, and adductor longus are supplied by the obturator nerve. Injuries of the obturator nerve are
uncommon, but one cause in such cases is compression of the nerve between the fetal head and
the pelvic wall during prolonged labor.
2012
What do fibrillation potentials represent?
A. Spontaneous depolarization of the muscle fiber
B. Demyelination of peripheral nerves
C central nervous system pathology
d activation of the motor unit
A is correct
Fibrillation potentials are simply spontaneous depolarizations of a single muscle fiber seen in pathologic tissue and are often elicited with needle movement while performing electromyography (EMG). Fibrillation potentials are seen in neurogenic conditions with acute or chronic axonal loss, but also in myopathic disease. Fibrillations are not characteristic for central nervous system disease states or conduction block. Conduction block is evaluated on nerve conduction studies. However, fibrillations could be seen in cases of conduction block if axonal loss has occurred as well.
2014
A 35-year-old man presents with left foot drop due to a fracture of his left tibia in a motor vehicle crash. He is stable after reduction and plating. Since the surgery, he has weakness in his left leg and numbness along the dorsum of his foot. Electrodiagnostic testing yields the following results:
MOTOR NERVE CONDUCTION STUDIES (Normal values are in parentheses)
Nerve Stimulation Site Distal Latency (ms) Amplitude (mV) NCV (m/s)
L Peroneal (EDB) Ankle 4.4 (≤ 5.5) 5.1 (≥ 3.5) Below fibular head 4.8 (≥ 3.5) 46 (≥ 40) Knee 2.1 (≥ 3.5) 34 (≥ 40)
L Tibial (AH) Ankle 5.2 (≤ 6.0) 10.4 (≥ 3.5) Popliteal fossa 9.8 (≥ 3.5) 45 (≥ 40)
R Peroneal (EDB) Ankle 4.6 (≤5.5) 4.8 (≥ 3.5) Below fibular head 4.7 (≥ 3.5) 44 (≥ 40) Knee 4.7 distal latency 4.4 (≥ 3.5) 49 (≥ 40)
Abbreviations: EDB,extensor digitorum brevis; AH, abductor hallucis; NCV, nerve conduction velocity
SENSORY NERVE CONDUCTION STUDIES (Normal NCS values are in parentheses)
Nerve Stimulation site Recording Site Distal Latency (ms) Amplitude (µV)
L Superficial peroneal Leg - 12 cm Anterior ankle 3.3 (≤ 3.5) 4 (≥ 20)
R Superficial peroneal Leg - 12 cm Anterior ankle 3.2 (≤ 3.5) 21 (≥ 20)
L Sural sensory Calf - 14 cm Ankle 3.9 (≤ 4.4) 10 (≥ 8)
NEEDLE ELECTROMYOGRAPHY
Muscle
Abnormal Spontaneous Activity
Recruitment
L Tensor fascia lata
0
Normal
L Biceps femoris, long head
0
Normal
L Biceps femoris short head
0
Normal
L Anterior tibialis
2+
Reduced
L Peroneal longus
2+
Reduced
L Tibialis posterior
0
Normal
L Gastrocnemius
0
Normal
L Vastus medialis
0
Normal
L Lumbar paraspinals
0
Normal
R Anterior tibialis
0
Normal
R Gastrocnemius
0
Normal
R Vastus medialis
0
Normal
What injury do these test results reveal?
Option d is correct.
This patient presents with a left common peroneal mononeuropathy following a surgical procedure. There is evidence of focal slowing with partial conduction block at the fibular head and an abnormal superficial peroneal sensory NCS compared to the contralateral side. These findings would imply a compressive injury at the fibular head. Furthermore, needle EMG reveals abnormal spontaneous activity in muscles distal to the fibular head innervated by the branches of the left common peroneal nerve (superficial peroneal and deep peroneal nerves). The tibial nerve conduction studies are completely normal.
2014
Positive sharp waves and fibrillation potentials are most likely to be seen in which condition?
A Anterior horn cell disease
B Steroid myopathy
C Small fiber neuropathy
D Cerebellar ischemia
Option A is correct
Positive sharp waves (PSWs) and fibrillation potentials are seen in certain disorders of the muscles, neurogenic disease, and neuromuscular disorders. These may include but are not limited to inflammatory myositis, inclusion body myositis, rhabdomyolysis, anterior horn cell disorders, radiculopathies, plexopathies, peripheral neuropathies, myasthenia gravis, and botulism. Steroid myopathy does not result in muscle necrosis and thus abnormal spontaneous activity is not observed. Fibrillation potentials and PSWs are not characteristic for central nervous system pathology. Small fiber neuropathies will be undetected on needle EMG.
2014
Which statement is most correct regarding instrumentation for electrodiagnostic studies?
a. Signals pass from the filters to the amplifiers.
b.Cathode-ray tube subtracts common electrical activity.
c.Electrical signals are transmitted from 2 surface electrodes.
d Filters are used to increase the electrical noise.
Option c is correct.
Electrical signals are transmitted from skin surface electrodes or through a needle. These electrodes are referred to as E1 and E2 or the active and the reference. Differential amplifiers eliminate signal common to the 2 electrodes. Filters are used to remove excessive electrical noise after signal amplification. Cathode-ray tube permits the visual display of the electrical signal as a waveform.
2014
