Increased Prevalence of Myasthenia Gravis in a Cohort of Patients with Inflammatory Bowel Disease

Abstract Background. Co-morbid auto-immune disorders may affect 0.2% of the population. We evaluated the association between myasthenia gravis and inflammatory bowel disease. Methods. We present the epidemiological, clinical and electrodiagnostic findings of one patient with ulcerative colitis and three with Crohn’s disease (from a Brazilian cohort of 606 patients) and co-morbid myasthenia gravis. Results. Mean age of onset of inflammatory bowel disease was 33.5 + 2.7, and patients are currently 45.8 + 7.3 years old. Two patients were acetylcholine receptor antibody positive, one anti-Muscle specific kinase positive and one seronegative. Three had abnormal repetitive nerve stimulation, all four had normal nerve conduction studies, abnormal skin wrinkling test and mild small fiber neuropathy. None had thymoma and/or accepted thymectomy. According to the Myasthenia Gravis Foundation classification, one was class V, one class IVb and two IIa. Myasthenia gravis diagnosis was masked by immunotherapy in all. The Prevalence ratio of having myasthenia gravis in inflammatory bowel disease patients in comparison with the proportion of myasthenia gravis among all patients seen in our center was 8.56 (P<0.0001, CI=3.1-23.5). Considering the lowest and highest prevalence of myasthenia gravis reported in the literature, the Prevalence ratio is 44.0 (P<0.0001, CI:16.3-118.4) and 26.4 (P<0.0001, CI: 9.8-70.6), respectively. Conclusions. Myasthenia gravis prevalence is higher in inflammatory bowel disease and may include muscle specific kinase positive disease (first report in the literature). In general, myasthenia gravis clinical course was not significantly modified by inflammatory bowel disease relapses and frequently overlaps with other autoimmune conditions and small fiber neuropathy.