Eighteen patients are described, all of whom had chronic demyelinating peripheral neuropathy and benign IgM paraproteinaemia. All patients had serum antibodies against peripheral nerve myelin or myelin-associated glycoprotein. Seventeen were followed up clinically and electrophysiologically for between 1 and 14 years (mean 7.4 years). The presenting symptoms and signs were almost always those of a distal sensory disturbance in the limbs followed by distal weakness. All patients developed tremor or ataxia in the arms, and gait ataxia. The severity of the neuropathy varied greatly between patients at similar stages. Some had a predominantly sensory deficit and others a predominantly motor deficit. All patients eventually developed both motor and sensory signs. The neuropathy became slowly worse over the first 2-5 years and then appeared to stabilize, although long-term follow-up did reveal a very slow progression in the group as a whole. No patient developed evidence of haematological malignancy but two patients died of malignancy involving other systems. On reviewing 75 patients from the literature, non-haematological malignancy was found to be the commonest cause of death.

Twelve cases of chronic sensorimotor neuropathy associated with benign IgM paraproteinaemia are described. The onset was in the sixth or seventh decades and 9 cases were male. Tremor and ataxia were common features. The ESR was raised in 6 cases and the CSF protein content elevated in 10. There was severe reduction of motor nerve conduction velocity. Sera from all cases contained monoclonal IgM antibodies strongly reactive with human peripheral myelin, made up by the paraprotein. Histological studies on nerve biopsies taken from 8 cases all demonstrated a demyelinating neuropathy. Eight biopsies were examined by immunofluorescence. Monoclonal IgM was present on the myelin sheaths of surviving myelinated nerve fibres. The findings suggested that the neuropathy was of autoimmune origin and caused directly by the antimyelin antibody.

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