Neuromuscular disorders

Question 1

Motor unit components

Answer 1

• Anterior horn cell (LMN cell body)
• Peripheral nerve axon + myelin
• Neuromuscular junction
• Muscle
• Diseases of anterior horn cell or peripheral axon/myelin are called neurogenic
• Diseases of neuromuscular junction are called junctional d/o
• Diseases of the muscle are called myopathic d/o

Question 2

Sx localization of lesions

Answer 2

• Muscle weakness distribution (proximal= more LMN, distal= more UMN)
• Presence or absence of sensory functioning, reflexes, fatigability
• Mode of spread (cranial-> limbs or vice versa)
• Presence or absence of cramps or fasiculations

Question 3

Serum CPK

Answer 3

• Serum creatine-phospho kinase
• Elevated in myopathic d/o (destruction of muscle tissue)
• Normal to slightly elevated in neurogenic, normal in junctional

Question 4

Nerve conduction

Answer 4

• Abnormal in neurogenic d/o
• If due to axonal degeneration, will see a normal or slightly decreased conduction velocity w/ a decrease in amplitude of evoked response
• If due to segmental demyelination will see conduction velocities greatly decreased

Question 5

Other neuromuscular tests

Answer 5

• Repetitive nerve stimulation studies: abnormal in NMJ d/o (tests for muscle fatigueability or facilitation)
• Electromyographic evaluation (EMG): at rest and during effort
• Muscle or nerve biopsy: histological staining

Question 6

Amyotrophic lateral sclerosis (ALS)

Answer 6

• Anterior horn cell d/o (motor neuron disease)
• Etiology is unknown
• Age of onset is in mid/later years of life
• Clinical presentation: purely motor w/ asymmetric muscle weakness (can be proximal, distal or bulbar, but usually distal)
• Usually associated w/ CST degeneration, starts at feet and progresses upwards
• There is sparing of EOMs and sphincter muscles
• Cramps and fasiculations are common initial symptoms
• Muscle atrophy w/ progression, finally respiratory and swallowing impairment

Question 7

Guillain barre syndrome (GBS)

Answer 7

• Demyelinating neuropathy
• Etiology: immune mediated
• Clinical presentation: starts in lower extremities then ascends to involve the upper extremities and cranial nerve muscles
• Sx: mild sensory but predominantly motor weakness
• Autonomic Sx very common, respiration involved during rapid progression
• Blood tests that may need to be done: HIV, campylobacter, lyme disease

Question 8

Myasthenia gravis

Answer 8

• NMJ d/o
• Etiology: autoimmune attack against nicotinic receptor, also associated w/ thymic abnormalities
• Age of onset: various (anytime)
• Clinical features: Sx begin in EOM and other cranial nerve muscles followed by proximal muscle weakness
• Also see fatigue ability worsened by activity
• Further Sx include ptosis, double vision, dysphagia, nasal voice, weak jaw closure and neck extensors, proximal muscle weakness and then respiratory muscle involvement
• One way to Dx is abnormal thymic tissue (hyperplasia and thymomas) on radiographs

Question 9

Lamber-eaton myasthenia syndrome (LEMS)

Answer 9

• Presynaptic d/o
• Etiology: autoimmune, often secondary to neoplasm (like small cell lung cancer)
• Age of onset: mid-late years
• Clinical features: fatigue, proximal muscle weakness and autonomic dysfunction (cholinergic hypofunction)

Question 10

Inflammatory myopathy

Answer 10

• Muscle cell d/o
• Etiology: autoimmune, associated w/ collagen vascular disease and can be a manifestation of remote CA
• Clinical presentation: begins w/ neck flexors, proximal muscle weakness, dysphagia and skin rash (dermatomyositis)
• Will progress if not Rx