CALCIUM-CHANNEL AUTOANTIBODIES IN MYASTHENIC SYNDROME AND SMALL-CELL LUNG-CANCER

Lambert-Eaton myasthenic syndrome (LEMS) is one of the neurologic para neoplastic syndromes often found in patients with lung cancer. It is c haracterized by a generalized deficit of neurotransmitter release. Pat ients with small cell lung cancer (SCLC) in particular may develop LEM S, and SCLC is very often detected in patients affected by LEMS. LEMS is an autoimmune disease, and autoantibodies that interfere with neuro transmitter release by binding to presynaptic voltage-operated calcium channels (VOCCs) have been found in sera of patients with LEMS. Both human neuronal and SCLC cell lines express omega-conotoxin-sensitive V OCCs, and autoantibodies from patients affected by LEMS can precipitat e these channels. We have now screened a large population of patients and control subjects in order to define the specificity and sensitivit y of the anti-VOCC antibody assay. We have tested sera from 52 patient s with LEMS with and without SCLC; 32 sera from patients with SCLC wit hout LEMS, 31 from patients with non-SCLC, 34 from patients with infla mmatory lung diseases, 17 from patients with other neurologic disorder s, and 48 from healthy control subjects. We have found that a positive result with this radioimmunoassay is highly specific for LEMS, with o r without SCLC, when the antibody titer is higher than 14.21 pM. Anti- VOCC antibodies have also been found in about 40% of patients with SCL C without LEMS, but they were absent in all the other populations test ed. We can conclude that this serologic assay is a very useful aid in the diagnosis of LEMS, and it might be useful also for the early diagn osis of SCLC.