PARANEOPLASTIC MYASTHENIA-GRAVIS - DETECTION OF ANTI-MGT30 (TITIN) ANTIBODIES PREDICTS THYMIC EPITHELIAL TUMOR

It has been suggested that antibodies against nonacetylcholine recepto r proteins of striated muscle are markers of the presence of a thymic epithelial tumor in patients with myasthenia gravis (MG). These antibo dies may be? measured using an immunofluorescence assay against striat ed muscle (anti-STR) or an ELISA with a recombinant 30-kd titin fragme nt (anti-MGT30). To directly compare anti-STR with anti-MGT30, we exam ined the sera of 276 consecutive patients with known or suspected MG. Definite diagnoses and thymic histology, if available, were correlated with the antibody assays. Of the 276 patients, 164 had MG. Thymic his tology was obtained in 44 patients: 18 had lymphofollicular hyperplasi a, 13 thymic epithelial tumors, 8 atrophy, and 5 were normal. When com pared with anti-STR, anti-MGT30 showed a sensitivity of 69% (STR 77%), specificity or 100% (STR 56%, p = 0.026), negative predictive value o r 82% (STR 77%), and positive predictive value of 100% (STR 56%, p = 0 .003) for the identification of a thymic epithelial tumor versus thymi c hyperplasia. We conclude that the anti-MGT30 ELISA is better than th e anti-STR immunofluorescence assay for the diagnosis of paraneoplasti c MG.