Comorbidities and disability trajectories in multiple sclerosis: A two-cohort study using multi-state Markov models

Background: Comorbidities are common in multiple sclerosis (MS) and may influence disability outcomes, but their dynamic impact on bidirectional disability transitions and long-term disability remains incompletely understood. Better understanding of this longitudinal relationship could inform personalized disability management strategies for people with MS. Methods: We leveraged two large electronic health record (EHR)-linked MS registries and applied multi-state Markov models (MSMs) to examine the extent to which individual comorbidities and overall comorbidity burden were associated with short-term disability transitions, long-term disability transition probabilities, and expected time spent in each disability state. We additionally compared MSM-based predictions of confirmed disability worsening (CDW) with Cox proportional hazards (CoxPH) model-based predictions using the integrated Brier score with bootstrap validation. Results: Among 3,723 patients with MS (74.6% female; 86.2% non-Hispanic White; mean age=41.9 years; mean disease duration=5.4 years) contributing 41,860 disability assessments over a mean follow-up of 7.3 years, higher cardiometabolic and psychiatric comorbidity burden was associated with increased transition intensity toward worse disability states and decreased transition intensity toward improvement, with a stepwise gradient across burden levels. Compared with patients without comorbidities, those with [≥]4 comorbidities had a 28% higher risk of worsening (HR=1.28 [1.06, 1.55]) and a 20% lower risk of improvement (HR=0.80 [0.67, 0.95]). Each individual comorbidity was significantly associated with worse disability transitions. Long-term estimates indicated a higher 5-year probability of severe disability and fewer years spent in the no-disability state among patients with greater comorbidity burden. CoxPH models showed directionally consistent associations but lower predictive accuracy for CDW compared with MSMs. Conclusion: Cardiometabolic and psychiatric comorbidities are associated with worse disability trajectories in MS, reducing improvement and accelerating progression. By providing a nuanced framework to quantify short-term disability transitions and long-term disability patterns, MSMs may have real-world clinical utility in disability prediction.