A prospective study of the incidence of sub-clinical Lambert-Eaton Myasthenic Syndrome (LEMS) in patients with small cell lung cancer (SCLC).

7213 Background: LEMS is one of the most common paraneoplastic disorders associated with SCLC. Autoantibodies targeted to the P/Q type voltage gated calcium channel (VGCC) are believed to be a cause of LEMS and form the basis of a diagnostic serological test. It is not known how many patients (pts) presenting with SCLC have positive anti-VGCC antibodies (Ab) and subclinical LEMS who may then be susceptible to develop clinical LEMS. We used a sensitive serological test to determine, in a prospective manner, the incidence of subclinical LEMS in SCLC. METHODS: Consenting Pts with a pathological diagnosis of SCLC completed a symptom questionnaire, had clinical examination for signs of LEMS, and serum for P/Q anti-VGCC Ab was taken. VGCC Abs were measured by immunoprecipitation of [I125]-labeled conotoxin MVIIC bound to VGCCs extracted from human cerebellum. Antibody titres were considered positive if >50pM (Mean +3SD for healthy controls n=30). Multivariate regression was used to determine the relationship between clinical symptoms and anti-VGCC titre, and Cox analysis to evaluate survival. RESULTS: Of the 64 pts (46 male 18 female) tested, 5 (8%) pts had elevation of the anti-VGCC antibodies with levels ranging from 69 to 1553pM. Only one had LEMS on clinical grounds, confirmed by electrophysiological tests. The other 4 patients did not have clinical evidence of LEMS. There was no association between anti-VGCC titre and survival (p=0.08, hazards ratio 0.999). CONCLUSIONS: This prospective study indicated that increased titre of anti-VGCC antibodies is common in SCLC. The presence of antibody positivity may help to identify patients who are at risk of developing the debilitating symptoms of LEMS. No significant financial relationships to disclose.