The occurrence of anti-titin antibodies and thymomas: A population survey of MG 1970-1999

To estimate the incidence of elevated anti-titin antibodies titers and of thymomas in a population of patients with MG using various statistics and associations. Extensive epidemiology, systematic measurement of anti-titin antibodies, and histologic assessment of thymomas according to the new World Health Organization classification. The mean annual incidence rate of MG per million population was 8.3. The analogous mean rate of thymomas was 2.0, out of which MG was encountered in about 20%. A thymoma was coexistent in 7% of the patients with MG. The finding of titin autoantibodies and the coexistence of thymomas were both associated with age at the appearance of MG. In patients with MG with a thymoma, the frequency of seropositivity was 68%, whereas acetylcholine receptor (AChR) autoantibodies were detected in all such sera. Titin autoantibody-positive sera were also anti-AChR antibodies positive. Further, all serum samples negative for anti-AChR antibodies were devoid of anti-titin antibodies. Titin autoantibodies were not detected in nonthymoma early-onset MG. Apart from MG with a thymoma, the finding of the titin autoantibodies was observed to be an exclusive feature of late-onset MG, the frequency being 55%. No data were found to suggest that patients with MG were more likely to present with thymic tumors than other patients exhibiting thymic neoplasia. In about 80%, such tumors in MG were composed of cortical cells. The concept of the anti-titin antibodies merely as a paraneoplastic marker in MG was not supported by these data.