Elevated triglyceride-glucose index and risk of thymoma-associated myasthenia gravis: a prospective analysis from the UK Biobank.
BACKGROUND: Thymoma-associated myasthenia gravis (MG) is a clinically significant but uncommon condition, affecting up to half of thymoma patients and associated with worse outcomes than either disease alone. Reliable biomarkers for early risk stratification remain scarce. The triglyceride-glucose (TyG) index and triglyceride-to-high-density lipoprotein cholesterol (TG/HDL-C) ratio are established biomarkers reflecting insulin resistance and dyslipidemia. However, their clinical associations with thymoma-associated MG remain incompletely characterized. METHODS: A total of 501,954 UK Biobank participants were included. After exclusions, 422,397 (313 cases) were analyzed for TyG index and 422,691 (314 cases) for TG/HDL-C ratio. Exposures were stratified into quartiles, and assessed continuously per unit increase. Cox proportional hazards models estimated hazard ratios (HRs), restricted cubic splines (RCS) assessed non-linear associations, and subgroup analyses were stratified by body mass index (BMI). Sensitivity analyses examined TyG index and MG alone. RESULTS: An elevated TyG index was associated with increased risk of thymoma-associated MG. Compared to Q1, Q4 had higher risk (HR = 1.66, 95% CI: 1.20-2.31, P = 0.003); the overall HR per unit increase was 1.42 (95% CI: 1.17-1.73, P = 0.0005). TG/HDL-C ratio showed similar patterns: Q4 vs Q1 HR = 1.54 (95% CI: 1.11-2.15, P = 0.01); overall HR per unit increase was 1.06 (95% CI: 1.02-1.10, P = 0.002). Non-linear relationships were observed, with suggested inflection points at TyG index 8.7 and TG/HDL-C ratio 2.8, rather than strict thresholds. Subgroup analyses revealed stronger associations in normal-weight and obese participants, although tests for interaction were not statistically significant. Sensitivity analyses confirmed consistent associations between TyG index and MG risk, including for isolated MG. CONCLUSION: Elevated TyG index and TG/HDL-C ratio were independently associated with higher thymoma-associated MG risk in this large prospective cohort, with evidence of non-linear relationships and BMI-related heterogeneity. These findings provide novel epidemiologic evidence linking metabolic markers of insulin resistance with thymoma-associated MG, but clinical translation requires further validation.