The prevalence of myasthenia gravis is increased in inflammatory bowel disease.

Comorbid autoimmune disorders affect approximately 0.2% of the population. A second autoimmune disease occurs in up to 15% of myasthenia gravis (MG) patients.To evaluate the association between MG and inflammatory bowel disease (IBD).We conducted a cross-sectional study involving a Brazilian cohort of IBD patients and a literature review.In 2022, we found 1 MG patient with ulcerative colitis and 3 with Crohn's disease out of 606 IBD patients (0.66% prevalence). The patient with UC and MG died in April 2024. The mean IBD onset age was 33.5 ± 2.7; patients were 45.8 ± 7.3-years-old at evaluation. Further, 2 patients were acetylcholine receptor antibody positive, 1 was anti-muscle specific kinase positive, and 1 seronegative. Also, 3 had abnormal repetitive nerve stimulation, all had normal nerve conduction studies, abnormal skin wrinkling test, and mild small fiber neuropathy. None had thymoma and/or underwent thymectomy. According to the MG Foundation's classification, one was class V, one IVb, and two IIa. The MG diagnosis was masked by immunotherapy in all. The prevalence ratio of MG in IBD patients versus the proportion of MG among all patients in our center was 8.56 (p < 0.0001, CI = 3.1-23.5). Considering the lowest and highest prevalence of this condition reported in the literature, the ratio is 44.0 (p < 0.0001, CI: 16.3-118.4) and 26.4 (p < 0.0001, CI: 9.8-70.6), respectively.The prevalence of MG is higher in IBD, may include muscle specific kinase positive disease (first report in the literature) and frequently overlaps with other autoimmune conditions and small fiber neuropathy.