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Lower motor lesion Flashcards

1
Q

What is a lower motor neuron (LMN) lesion?

A

A lesion affecting the motor neurons that directly innervate skeletal muscles, typically located in the anterior horn of the spinal cord, brainstem, or peripheral nerves.

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2
Q

What are fasciculations, and how are they related to LMN lesions?

A

Fasciculations are involuntary muscle twitches, often seen in LMN lesions as a sign of ongoing denervation.

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2
Q

What happens to deep tendon reflexes in LMN lesions?

A

Hyporeflexia or areflexia (absent or diminished reflexes) is common.

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3
Q

What type of weakness is associated with LMN lesions?

A

Flaccid weakness with reduced muscle tone (hypotonia).

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4
Q

How does muscle atrophy appear in LMN lesions?

A

Muscle atrophy is pronounced due to lack of neural input to the muscles.

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5
Q

What is the typical muscle tone in LMN lesions?

A

Muscle tone is typically reduced or flaccid.

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6
Q

What does a normal Babinski sign indicate in an LMN lesion?

A

A normal Babinski sign (flexion of the toes) is typically present in LMN lesions.

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7
Q

What types of reflex changes are seen in LMN lesions?

A

Decreased or absent reflexes, also known as hyporeflexia or areflexia.

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8
Q

How is the gait affected in LMN lesions?

A

Gait can be weak or waddling, depending on which muscles are affected.

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9
Q

What type of motor unit activity is seen in electromyography (EMG) for LMN lesions?

A

Denervation potentials, such as fibrillations and positive sharp waves.

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9
Q

How does an LMN lesion affect the distribution of weakness?

A

Weakness is typically focal and follows the distribution of affected nerves or spinal segments.

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10
Q

How can sensory changes help differentiate between LMN and UMN lesions?

A

LMN lesions often accompany sensory loss if the peripheral nerve is affected, whereas UMN lesions typically do not.

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11
Q

What causes flaccid paralysis in LMN lesions?

A

Loss of input from motor neurons to the muscles results in flaccid paralysis.

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12
Q

How is muscle tone different in LMN lesions compared to UMN lesions?

A

LMN lesions result in hypotonia or flaccidity, while UMN lesions cause spasticity.

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13
Q

What is the difference between primary and secondary atrophy in LMN lesions?

A

Primary atrophy is due to direct denervation of muscles, while secondary atrophy occurs due to disuse.

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14
Q

What part of the motor system is affected by LMN lesions?

A

The anterior horn cells, cranial nerve motor nuclei, and peripheral nerves.

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15
Q

How do LMN lesions affect speech if cranial nerves are involved?

A

Dysarthria (slurred speech) can occur if cranial nerves, such as the hypoglossal nerve, are affected.

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16
Q

What is the typical progression of muscle atrophy in LMN lesions?

A

Atrophy usually progresses over time, especially in long-standing LMN lesions.

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17
Q

What cranial nerve palsies are commonly seen with LMN lesions?

A

LMN lesions can involve facial nerve palsy, hypoglossal nerve palsy, or oculomotor nerve palsy.

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18
Q

What can cause LMN lesions in the peripheral nerves?

A

Peripheral neuropathies, trauma, or compression (e.g., carpal tunnel syndrome).

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18
Q

How does the presence of fasciculations help diagnose LMN lesions?

A

Fasciculations are characteristic of LMN lesions due to motor unit instability.

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19
Q

What is the most common cause of LMN lesions affecting the anterior horn cells?

A

Amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy (SMA) are common causes.

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20
Q

How can Guillain-Barré syndrome present as an LMN lesion?

A

It causes ascending paralysis with LMN signs like hyporeflexia and flaccidity.

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21
Q

What is the difference between radiculopathy and peripheral neuropathy in LMN lesions?

A

Radiculopathy affects nerve roots, while peripheral neuropathy affects distal nerves.

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22
What is the role of nerve conduction studies (NCS) in diagnosing LMN lesions?
NCS can show slowed conduction velocities or decreased amplitude, indicating peripheral nerve damage.
23
What reflex finding would you expect in a patient with an LMN lesion in the sciatic nerve?
Absent ankle reflex and weakness in leg muscles innervated by the sciatic nerve.
24
How do LMN lesions of the facial nerve typically present?
Bell’s palsy, which causes unilateral facial weakness affecting both upper and lower facial muscles.
25
What is the hallmark of an LMN lesion in spinal muscular atrophy (SMA)?
Progressive muscle wasting and weakness, especially in the limbs.
26
What is the typical reflex pattern in Guillain-Barré syndrome?
Reflexes are often diminished or absent in Guillain-Barré syndrome.
27
How can polio lead to LMN lesions?
Poliovirus attacks the anterior horn cells, causing flaccid paralysis and atrophy.
28
How does the involvement of multiple peripheral nerves appear in LMN lesions?
Multiple nerve involvement, or polyneuropathy, leads to symmetric weakness and sensory loss.
29
How does the distribution of weakness in a single nerve lesion help localize an LMN lesion?
Weakness follows the distribution of the specific nerve affected, such as the radial or ulnar nerve.
29
How does motor neuron disease affect LMN function?
Motor neuron disease causes degeneration of motor neurons, leading to LMN signs like atrophy and fasciculations.
30
What can cause an isolated LMN lesion in the ulnar nerve?
Compression at the elbow or trauma can lead to an isolated ulnar nerve lesion.
31
How does the recovery of LMN lesions differ from UMN lesions?
LMN lesion recovery is often slower and may be incomplete due to permanent damage to motor neurons.
31
What role does physical therapy play in managing LMN lesions?
Physical therapy helps prevent secondary complications like contractures and aids in muscle strengthening.
31
What is the presentation of an LMN lesion affecting the phrenic nerve?
Diaphragmatic weakness, leading to respiratory issues.
32
How does radiculopathy in the lumbar region present as an LMN lesion?
It causes lower back pain, radiating leg weakness, and diminished reflexes in the legs.
33
What is the typical motor response in an acute LMN lesion?
Flaccid paralysis and loss of voluntary movement.
34
How do dermatomal sensory losses aid in localizing LMN lesions?
Dermatomal patterns help identify which spinal root is involved in radiculopathy.
35
How are reflexes altered in LMN lesions during an exam?
Reflexes are typically reduced or absent (hyporeflexia or areflexia) in muscles innervated by the affected nerves.
35
What is the primary feature to look for in LMN lesions during a neurological exam?
Muscle weakness, atrophy, and fasciculations in the affected muscles.
36
How does muscle tone help localize an LMN lesion?
Affected muscles will have reduced or flaccid muscle tone (hypotonia or flaccidity).
37
How do you check for fasciculations during the neurological exam?
Inspect muscles at rest for fine, twitching movements (fasciculations), especially in affected areas like the arms or legs.
38
Which reflex tests should be performed to localize an LMN lesion?
Test the deep tendon reflexes (e.g., biceps, triceps, patellar, and Achilles) in the affected limb to look for diminished or absent responses.
39
How does muscle atrophy appear in an LMN lesion during a neurological exam?
Observe for visible muscle wasting or reduction in muscle bulk in the affected region.
40
What sensory signs might help localize an LMN lesion?
LMN lesions often have associated sensory deficits, so check for numbness or loss of sensation in the distribution of the affected peripheral nerve or nerve root.
41
How does testing muscle power aid in localizing an LMN lesion?
Manual muscle testing will show weakness localized to the muscles innervated by the damaged nerve.
42
How can you distinguish between a single nerve lesion and a nerve root lesion in LMN localization?
Peripheral nerve lesions result in focal deficits in the distribution of one nerve, while nerve root lesions (radiculopathy) affect muscles and skin in a dermatomal and myotomal distribution.
43
What should you observe when assessing gait in an LMN lesion?
Look for a foot drop, waddling gait, or limp, depending on which muscles are weak or paralyzed.
44
How do you perform sensory testing to localize an LMN lesion?
Test light touch, pinprick, and vibration sensation in areas innervated by the suspected nerve or nerve root.
44
How does the biceps reflex help localize an LMN lesion?
A diminished biceps reflex suggests an LMN lesion in the C5-C6 nerve root or the musculocutaneous nerve.
45
How does the Achilles reflex help localize an LMN lesion?
Loss of the Achilles reflex suggests an LMN lesion at the S1 nerve root or the tibial nerve.
45
How can a cranial nerve examination help localize an LMN lesion?
LMN lesions affecting cranial nerves (e.g., facial nerve palsy) can present with unilateral weakness or paralysis of muscles supplied by the affected nerve.
45
How does a foot drop help localize an LMN lesion?
A foot drop indicates a lesion in the common peroneal nerve or L5 root, causing weakness in dorsiflexion.
45
How can the patellar reflex help localize an LMN lesion?
A diminished or absent patellar reflex suggests an LMN lesion at the L3-L4 nerve roots or the femoral nerve.
46
How does an absent triceps reflex localize an LMN lesion?
Loss of the triceps reflex suggests a lesion in the C7 nerve root or the radial nerve.
46
What finding in the intrinsic hand muscles suggests an LMN lesion?
Atrophy and weakness of the intrinsic hand muscles suggest an LMN lesion in the ulnar nerve or C8-T1 nerve roots.
47
How do fasciculations in the tongue help localize an LMN lesion?
Tongue fasciculations indicate an LMN lesion affecting the hypoglossal nerve (cranial nerve XII).
47
How does wrist drop help localize an LMN lesion?
A wrist drop suggests an LMN lesion in the radial nerve.
48
How does sensory loss in the hand help localize an LMN lesion?
Sensory loss in the ulnar distribution (medial hand) suggests an ulnar nerve lesion, while sensory loss in the radial or median nerve areas suggests corresponding nerve damage.
48
What does atrophy of the quadriceps muscle suggest?
Atrophy of the quadriceps muscle suggests an LMN lesion in the femoral nerve or L3-L4 nerve roots.
48
How does the distribution of weakness in a lower limb help localize an LMN lesion?
Localized weakness in the anterior thigh suggests a lesion in the femoral nerve, while weakness in the posterior leg indicates the sciatic nerve.
49
How does a foot slap help localize an LMN lesion?
A foot slap during gait suggests weakness in dorsiflexion, indicating a lesion in the L5 nerve root or common peroneal nerve.
49
How does muscle tone in the lower limb help localize an LMN lesion?
Reduced muscle tone (flaccidity) in one leg or localized area points to a nerve root or peripheral nerve lesion.
49
How do you distinguish an LMN lesion from a myopathy during an exam?
LMN lesions show asymmetrical, focal weakness, while myopathies present with symmetric weakness and no sensory loss.
50
What does the absence of the cremasteric reflex indicate?
An absent cremasteric reflex suggests an LMN lesion at the L1-L2 level or in the ilioinguinal nerve.
51
How do you test for an LMN lesion affecting the ulnar nerve?
Test for weakness in finger abduction and observe hypothenar atrophy.
52
How do changes in muscle tone help differentiate LMN lesions from UMN lesions?
Decreased tone (flaccidity) points to an LMN lesion, while increased tone (spasticity) suggests an UMN lesion.
53
What does weakness in shoulder abduction suggest during an LMN localization?
Weakness in shoulder abduction suggests an LMN lesion in the C5 nerve root or axillary nerve.

Neurology (8 decks)

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