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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
Q

What is the role of nerve conduction studies (NCS) in diagnosing LMN lesions?

A

NCS can show slowed conduction velocities or decreased amplitude, indicating peripheral nerve damage.

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23
Q

What reflex finding would you expect in a patient with an LMN lesion in the sciatic nerve?

A

Absent ankle reflex and weakness in leg muscles innervated by the sciatic nerve.

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24
Q

How do LMN lesions of the facial nerve typically present?

A

Bell’s palsy, which causes unilateral facial weakness affecting both upper and lower facial muscles.

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25
Q

What is the hallmark of an LMN lesion in spinal muscular atrophy (SMA)?

A

Progressive muscle wasting and weakness, especially in the limbs.

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26
Q

What is the typical reflex pattern in Guillain-Barré syndrome?

A

Reflexes are often diminished or absent in Guillain-Barré syndrome.

27
Q

How can polio lead to LMN lesions?

A

Poliovirus attacks the anterior horn cells, causing flaccid paralysis and atrophy.

28
Q

How does the involvement of multiple peripheral nerves appear in LMN lesions?

A

Multiple nerve involvement, or polyneuropathy, leads to symmetric weakness and sensory loss.

29
Q

How does the distribution of weakness in a single nerve lesion help localize an LMN lesion?

A

Weakness follows the distribution of the specific nerve affected, such as the radial or ulnar nerve.

29
Q

How does motor neuron disease affect LMN function?

A

Motor neuron disease causes degeneration of motor neurons, leading to LMN signs like atrophy and fasciculations.

30
Q

What can cause an isolated LMN lesion in the ulnar nerve?

A

Compression at the elbow or trauma can lead to an isolated ulnar nerve lesion.

31
Q

How does the recovery of LMN lesions differ from UMN lesions?

A

LMN lesion recovery is often slower and may be incomplete due to permanent damage to motor neurons.

31
Q

What role does physical therapy play in managing LMN lesions?

A

Physical therapy helps prevent secondary complications like contractures and aids in muscle strengthening.

31
Q

What is the presentation of an LMN lesion affecting the phrenic nerve?

A

Diaphragmatic weakness, leading to respiratory issues.

32
Q

How does radiculopathy in the lumbar region present as an LMN lesion?

A

It causes lower back pain, radiating leg weakness, and diminished reflexes in the legs.

33
Q

What is the typical motor response in an acute LMN lesion?

A

Flaccid paralysis and loss of voluntary movement.

34
Q

How do dermatomal sensory losses aid in localizing LMN lesions?

A

Dermatomal patterns help identify which spinal root is involved in radiculopathy.

35
Q

How are reflexes altered in LMN lesions during an exam?

A

Reflexes are typically reduced or absent (hyporeflexia or areflexia) in muscles innervated by the affected nerves.

35
Q

What is the primary feature to look for in LMN lesions during a neurological exam?

A

Muscle weakness, atrophy, and fasciculations in the affected muscles.

36
Q

How does muscle tone help localize an LMN lesion?

A

Affected muscles will have reduced or flaccid muscle tone (hypotonia or flaccidity).

37
Q

How do you check for fasciculations during the neurological exam?

A

Inspect muscles at rest for fine, twitching movements (fasciculations), especially in affected areas like the arms or legs.

38
Q

Which reflex tests should be performed to localize an LMN lesion?

A

Test the deep tendon reflexes (e.g., biceps, triceps, patellar, and Achilles) in the affected limb to look for diminished or absent responses.

39
Q

How does muscle atrophy appear in an LMN lesion during a neurological exam?

A

Observe for visible muscle wasting or reduction in muscle bulk in the affected region.

40
Q

What sensory signs might help localize an LMN lesion?

A

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
Q

How does testing muscle power aid in localizing an LMN lesion?

A

Manual muscle testing will show weakness localized to the muscles innervated by the damaged nerve.

42
Q

How can you distinguish between a single nerve lesion and a nerve root lesion in LMN localization?

A

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
Q

What should you observe when assessing gait in an LMN lesion?

A

Look for a foot drop, waddling gait, or limp, depending on which muscles are weak or paralyzed.

44
Q

How do you perform sensory testing to localize an LMN lesion?

A

Test light touch, pinprick, and vibration sensation in areas innervated by the suspected nerve or nerve root.

44
Q

How does the biceps reflex help localize an LMN lesion?

A

A diminished biceps reflex suggests an LMN lesion in the C5-C6 nerve root or the musculocutaneous nerve.

45
Q

How does the Achilles reflex help localize an LMN lesion?

A

Loss of the Achilles reflex suggests an LMN lesion at the S1 nerve root or the tibial nerve.

45
Q

How can a cranial nerve examination help localize an LMN lesion?

A

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
Q

How does a foot drop help localize an LMN lesion?

A

A foot drop indicates a lesion in the common peroneal nerve or L5 root, causing weakness in dorsiflexion.

45
Q

How can the patellar reflex help localize an LMN lesion?

A

A diminished or absent patellar reflex suggests an LMN lesion at the L3-L4 nerve roots or the femoral nerve.

46
Q

How does an absent triceps reflex localize an LMN lesion?

A

Loss of the triceps reflex suggests a lesion in the C7 nerve root or the radial nerve.

46
Q

What finding in the intrinsic hand muscles suggests an LMN lesion?

A

Atrophy and weakness of the intrinsic hand muscles suggest an LMN lesion in the ulnar nerve or C8-T1 nerve roots.

47
Q

How do fasciculations in the tongue help localize an LMN lesion?

A

Tongue fasciculations indicate an LMN lesion affecting the hypoglossal nerve (cranial nerve XII).

47
Q

How does wrist drop help localize an LMN lesion?

A

A wrist drop suggests an LMN lesion in the radial nerve.

48
Q

How does sensory loss in the hand help localize an LMN lesion?

A

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
Q

What does atrophy of the quadriceps muscle suggest?

A

Atrophy of the quadriceps muscle suggests an LMN lesion in the femoral nerve or L3-L4 nerve roots.

48
Q

How does the distribution of weakness in a lower limb help localize an LMN lesion?

A

Localized weakness in the anterior thigh suggests a lesion in the femoral nerve, while weakness in the posterior leg indicates the sciatic nerve.

49
Q

How does a foot slap help localize an LMN lesion?

A

A foot slap during gait suggests weakness in dorsiflexion, indicating a lesion in the L5 nerve root or common peroneal nerve.

49
Q

How does muscle tone in the lower limb help localize an LMN lesion?

A

Reduced muscle tone (flaccidity) in one leg or localized area points to a nerve root or peripheral nerve lesion.

49
Q

How do you distinguish an LMN lesion from a myopathy during an exam?

A

LMN lesions show asymmetrical, focal weakness, while myopathies present with symmetric weakness and no sensory loss.

50
Q

What does the absence of the cremasteric reflex indicate?

A

An absent cremasteric reflex suggests an LMN lesion at the L1-L2 level or in the ilioinguinal nerve.

51
Q

How do you test for an LMN lesion affecting the ulnar nerve?

A

Test for weakness in finger abduction and observe hypothenar atrophy.

52
Q

How do changes in muscle tone help differentiate LMN lesions from UMN lesions?

A

Decreased tone (flaccidity) points to an LMN lesion, while increased tone (spasticity) suggests an UMN lesion.

53
Q

What does weakness in shoulder abduction suggest during an LMN localization?

A

Weakness in shoulder abduction suggests an LMN lesion in the C5 nerve root or axillary nerve.

Neurology (8 decks)

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