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Lambert-Eaton myasthenic syndrome (LEMS) is a presynaptic disorder of neuromuscular transmission characterised by impaired quantal release of acetylcholine that causes proximal weakness, depressed tendon reflexes, and post-tetanic potentiation; additionally, autonomic changes are present. 1 2 About 60% of patients have a small cell lung cancer (SCLC). 3 Evidence that it is an autoimmune disease mediated by antibodies to voltage gated calcium channels (VGCCs) at motor nerve terminals includes the clinical response to plasma exchange, 4 the passive transfer of the pathophysiological and morphological changes to mice by injection of patients' immunoglobulins, 4-7 and the detection by radioimmunoassay of serum antibodies in patients with LEMS to P/Q-type VGCCs. 8 9 The antigenic stimulus for anti-VGCC autoantibody production in patients with SCLC-LEMS seems to be tumour VGCCs 10 ; the trigger for the production of anti-VGCC antibodies in patients with LEMS with no detectable lung cancer (non-SCLC-LEMS) is unknown.
Prognosis in autoimmune diseases is variable. Most chronic autoimmune diseases are associated with reduced life expectancy. 11 In myasthenia gravis, spontaneous long lasting remissions can occur in up to 20% of patients, and, after surgical and immunosuppressive treatment, at least 70% of patients are well or have only minimal restrictions 3 to 5 years after disease onset. 12
There have been no long term follow up studies of patients with non-SCLC-LEMS although mortality statistics are available on patients with SCLC-LEMS. 3 13 14 We therefore undertook a prospective study of patients with non-SCLC-LEMS seen from September 1996 to October 1998, and combined this with a retrospective study of similar patients seen before that date.
Methods
PATIENTS
We analysed the case records of 47 consecutive patients with LEMS without clinical or radiological evidence of SCLC seen in Oxford by one of us (JN-D) between December 1987 and October 1998. The diagnosis was based on typical clinical features and the presence of either characteristic EMG changes or raised VGCC titres. The EMG criteria comprised a reduced compound muscle action potential (CMAP) amplitude in abductor digiti minimi (ADM) (<8.5 mV) 15 16 ; and a CMAP amplitude increment of more than 100% after 10 seconds maximal voluntary contraction. Serum VGCC antibody concentrations were significantly raised in 86%. A further 15 patients with LEMS with SCLC were also seen during the study...