Increased Prevalence of Extrathymic Neoplasms in Myasthenia Gravis Patients-A Population-Based, Matched Case-Control...

Myasthenia gravis (MG) is associated with thymic neoplasms. However, an increased prevalence of extrathymic neoplasms has also been reported. This study aimed to evaluate the rates of malignancy in MG patients while accounting for risk factors such as disease characteristics and immunomodulatory treatments.

We conducted a case-control study using the Clalit Health Services database, applying a machine learning (ML) algorithm to minimize diagnosis misclassification. We included MG patients aged 18 years and older, with a sex- and age-matched control group in a 1:3 ratio. We compared the prevalence and hazard ratios of extrathymic neoplasms between the groups.

A total of 1558 patients with a high probability of MG, according to our ML model, were included in the cohort, alongside a control group of 4674 individuals. MG patients had a higher prevalence of malignancy prior to MG diagnosis, with an odds ratio of 1.95 (95% CI, 1.65-2.08), and a higher incidence of malignancy after MG diagnosis, with a hazard ratio of 1.56 (95% CI, 1.38-1.77). The most prevalent extrathymic neoplasms after MG diagnosis were respiratory, intrathoracic, skin (specifically non-melanoma), urinary tract, soft tissue, and myelodysplastic syndrome. Risk factors for malignancy included age, male sex, and thymoma. Immunosuppressive treatment did not increase the risk of malignancy.

MG patients have a higher prevalence of both solid and hematologic neoplasms compared to non-myasthenic controls, regardless of immunosuppressive treatment. This supports the notion that malignancy is related to MG disease itself rather than external factors.