Acquired motor neuron disorders

The acquired motor neuron disorders are diverse conditions characterized by weakness and preserved sensory function. The cause of most of these disorders is poorly understood, and treatment is mainly supportive. ALS, the most common motor neuron disorder seen in practice, has UMN and-LMN signs, and typically begins focally, with diffuse spread to involve limb, bulbar, and respiratory muscles, causing death from respiratory failure. The cause of ALS is not known, but new evidence suggests that oxidative injury and a disturbance in glutamate metabolism play major roles. Riluzole slows progression slightly, and neurotrophic factors are being tested for possible benefit. Combination therapy for ALS is envisioned for the near future. Post- polio syndrome occurs many years after recovering from polio, and often involves fatigue and pain. Progression of weakness may occur, but is uncommon. Of several LMN syndromes, multifocal motor neuropathy must be sought by careful assessment for motor conduction block because this syndrome may mimic ALS, and is reversible with immune-modulating treatment.