Patients with myasthenia gravis (MG) frequently coexist with other autoimmune diseases, but the temporal relationship between prior autoimmune diagnoses and subsequent MG has not been clearly defined at a population level. This study aimed to quantify rates and temporal patterns of selected autoimmune diseases during the 10 years preceding an MG diagnosis using nationwide claims data from South Korea.
This retrospective, population-based cohort study used claims data from the Korean National Health Insurance Service covering 2010 through 2021. The study population included individuals aged 20 years or older. Cases of MG were identified by the International Classification of Diseases, 10th Revision code G70.0 combined with Rare Intractable Disease registration code V012.
Each MG case (n = 8,355) was matched with 10 control subjects (n = 83,550) on age, sex, and index year. The investigators assessed diagnoses of specific autoimmune conditions that occurred during the 10 years before the index year. Evaluated outcomes were autoimmune thyroid disease (AITD), systemic lupus erythematosus (SLE), seropositive rheumatoid arthritis (SRA), Sjögren syndrome (SjS), psoriasis, type 1 diabetes mellitus (T1DM), Crohn disease, and ulcerative colitis.
Rate ratios (RRs) and 95% confidence intervals (CIs) comparing patients who subsequently developed MG with matched controls were estimated using Poisson regression models. Analyses were stratified by three pre-index time windows: 0–2 years, 2–5 years, and 5–10 years before the index year to assess temporal patterns.
The analytic cohort comprised 8,355 patients with MG and 83,550 matched controls. The cohort had a mean age of 53.7 years (SD 16.0) and 44.1% were male.
Across the entire 10-year prediagnostic period, patients who later received an MG diagnosis had a higher rate of any autoimmune disease than matched controls (RR 2.12, 95% CI 1.97–2.28). The excess was most pronounced in the 0–2 years before MG diagnosis (RR 4.27, 95% CI 3.78–4.83), indicating a clustering of autoimmune diagnoses in the immediate prediagnostic interval.
When individual autoimmune conditions were examined, several showed strong associations with subsequent MG over the 10-year prediagnostic window and particularly in the closest interval to diagnosis:
Two conditions showed associations confined to the 0–2 year prediagnostic period:
Crohn disease and ulcerative colitis were not associated with subsequent MG during the 10-year prediagnostic observation period.
In this national claims-based cohort, a higher frequency of several autoimmune diseases was observed in the years preceding an MG diagnosis compared with matched controls. The magnitude of association was greatest within 2 years before MG onset, suggesting that autoimmune comorbidity often clusters near the time MG is recognized clinically or that diagnostic attention increases in that period.
The strongest associations were seen for SLE, SjS, AITD, and SRA, indicating notable overlap between MG and systemic or organ-specific autoimmune conditions. Associations limited to the immediate prediagnostic window for psoriasis and T1DM may reflect variable temporal relationships across autoimmune conditions or differences in health-care contact patterns prior to MG diagnosis.
These findings support the concept that MG frequently occurs in the context of broader autoimmunity and that prior autoimmune diagnoses may be more common in patients who later develop MG.
The authors explicitly note limitations inherent to administrative claims data. Claims-based definitions may misclassify diagnoses or lack clinical detail (for example, serologic or electrophysiologic confirmation of MG or the autoimmune conditions). Temporal associations observed in claims data do not establish causality. The report does not provide individual-level clinical validation or data on potential mediators such as immunotherapy exposure, thymectomy status, or antibody profiles. Details beyond those reported in the abstract were not available in the source provided.
Within this nationwide South Korean cohort, a higher rate of several autoimmune diseases preceded MG diagnosis, most markedly within two years before MG onset. SLE, SjS, AITD, and SRA showed the strongest prediagnostic associations. The authors advise cautious interpretation because of the limitations of administrative claims data.