The case histories of 519 patients with peripheral neuropathy on whom sural nerve biopsy had been performed were reviewed. In 67 patients (50 males, 17 females) (13%) who had symptoms of a symmetrical polyneuropathy for more than one year, the cause remained undiagnosed in spite of intensive investigation. Patients with inflammatory neuropathy were not included, but represented 17% of the whole series. The mean age of onset of symptoms was 50.6 years, and the median time from onset of symptoms to initial investigation was 2 years. Males were affected more commonly than females in a ratio of 3:1. The clinical features in 43 patients were those of a mixed motor and sensory neuropathy, in 17 patients a predominantly sensory neuropathy and in 7 patients a predominantly motor neuropathy. The mean CSF protein was 0.73 g/l and in only six patients was it greater than 1 g/l. Nerve conduction studies most commonly demonstrated mild slowing of motor conduction and impairment of sensory conduction. The usual pathological changes on sural nerve biopsy were those of chronic axonal degeneration. Forty seven patients (70%) were re-examined at intervals of time which ranged from 4 months to 12 years after their initial presentation and nerve biopsy (median, 3 years). As a group, they were only mildly disabled, the condition had a very slowly progressive course and there had been little change in their disability. A possible aetiological factor was found in 17 of the 47 patients (36%) and included malignancy, alcoholism, and benign paraproteinaemia. It is concluded that with intensive investigation the cause of chronic polyneuropathy of duration greater than one year remains undetermined in only about 13% of patients and that continued follow-up is worthwhile since a diagnosis may be established on re-examination.
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