Macroglobulinemia with peripheral neuropathy simulating motor neuron disease

A 48‐year‐old man with an IgM plasma cell dyscrasia died after 14 months of symptoms and signs typical of motor neuron disease, including widespread fasciculation and normal sensation. Two laboratory results were atypical: cerebrospinal fluid protein content of 132 mg/dl and slow motor nerve conduction. At autopsy, no loss or atrophy of anterior horn neurons was found; instead, degeneration of ventral and dorsal roots and retrograde changes of chromatolysis in motor neurons implied peripheral neuropathy. Most reported cases of neuropathy associated with plasma cell dyscrasias have been sensorimotor or purely sensory, but there have been 14 previous cases of motor disorders.