A 25-year-old man with multifocal weakness and fasciculation was thought to have motor neuron disease. Signs progressed for 1 year, plateaued, and 3 years later resolved almost completely. There was no evidence of paraproteinemia, lymphoproliferative disorder, or vasculitis, and myelography was normal. Electrodiagnostic study disclosed multifocal, acute and chronic denervation that evolved into a picture consistent with residuals of old multifocal radiculopathy without active denervation. Prolongation of F response, absence of H-reflex, and conduction block in a proximal nerve segment suggested multifocal demyelination. A proximal motor neuropathy, perhaps demyelinating, may cause some of the benign motor neuron syndromes that simulate motor neuron disease.

No abstract

Abstract-The authors describe a 48-year-old man who presented with acute weakness. Serum K ϩ was 1.7 mmol/L, and investigations established hyperaldosteronism. Nerve excitability studies during hypokalemia demonstrated that axons were of high threshold with a fanning out of threshold electrotonus, consistent with hyperpolarization. Activity-dependent conduction block was induced by voluntary contraction. Excitability abnormalities resolved with K ϩ replacement. Activity-dependent conduction block induced by normal activity may contribute to weakness and paralysis developing with hypokalemia.

We report serial electrophysiologic observations in a patient with acute bulbar and respiratory paralysis following ingestion of saxitoxin-contaminated clams. Prolonged distal motor and sensory latencies, slowed conduction velocities, and moderately diminished amplitudes were present at the outset. All values returned to normal over 5 days. These findings, the result of incomplete sodium channel blockade, distinguish paralytic shellfish poisoning from most other acute paralytic illnesses.

Onion bulb formations involving cranial nerves are an unusual pathologic feature. We report the postmortem neuropathologic findings in a 69-year-old man with a longstanding neuropathy characterized by progressive muscle weakness, sensory ataxia and multiple cranial nerve abnormalities. Electrodiagnostic testing disclosed features of an acquired demyelinating polyneuropathy. Treatment with corticosteroids and plasmapheresis resulted in no change in his neurologic status, and the patient died after repeated episodes of pneumonia and sepsis. Autopsy showed widespread onion bulb formation in cranial nerves III, IV, V, VI, X, XI and XII, anterior and posterior spinal nerve roots, dorsal root ganglia and multiple peripheral nerves, some of which also had foci of epineurial perivascular inflammation. Muscle sections revealed severe neurogenic atrophy. This case demonstrates that, in longstanding acquired demyelinating neuropathy, the cranial nerves also undergo repetitive cycles of demyelination and remyelination resulting in severe weakness of the bulbar musculature and histologic features of hypertrophic neuropathy.