Amyotrophic lateral sclerosis

1. Big picture

Amyotrophic lateral sclerosis (ALS) is the classic disease of combined upper motor neuron and lower motor neuron degeneration. It is one of the most important motor neuron diseases in neurology because the patient develops progressive weakness, wasting, fasciculations, spasticity, bulbar dysfunction, and eventually respiratory failure.

The key exam sentence:

ALS causes progressive degeneration of both upper motor neurons and lower motor neurons, with no sensory loss, no eye movement disorder, and usually no bladder/bowel dysfunction.

The examiner usually wants you to recognize the combination:

• Upper motor neuron signs: spasticity, hyperreflexia, Babinski sign.
• Lower motor neuron signs: atrophy, fasciculations, cramps, flaccid weakness.
• Bulbar signs: dysarthria, dysphagia, tongue atrophy/fasciculations.
• Negative signs: preserved sensation, preserved ocular movements, preserved sphincters.

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