Serious infections in patients with myasthenia gravis: population-based cohort study

Objectives — To characterize the frequency and risk of serious infections in myasthenia gravis patients relative to age/sex/area-matched comparators.

Methods — This is a population-based cohort study in Ontario, Canada of newly-diagnosed MG patients and 1:4 age/sex/area-matched general population comparators accrued April 1, 2002 through December 31, 2015. The main outcome was a serious infection, defined by a primary diagnosis code on a hospitalization or emergency department record. We computed crude overall and sex-specific rates of infection among MG patients and comparators, and the frequency of specific types of infection. Adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated using Cox regression.

Results — Among 3,823 MG patients, 1,275 (33.4%) experienced a serious infection compared with 2,973/15,292 (19.4% of) comparators over a mean follow-up of over 5 years. Crude infection rates among MG patients were twice those in comparators (72.5 vs 35.0 per 1000 person years, respectively). The most common infection types were respiratory infections, particularly bacterial pneumonia. After adjustment for potential confounders, MG was associated with a 39% increased infection risk (adjusted HR: 1.39, 95% CI 1.28-1.51).

Conclusions — Patients with MG are at a significantly higher absolute and relative risk of serious infections compared to age/sex/area-matched comparators. This needs to be considered when selecting MG treatments and when planning vaccination / prophylaxis. Determining whether this risk is due to the use of immunosuppressive medications (versus MG itself) is an important area for future research.