Background Geographic gradients in multiple sclerosis (MS) incidence are well described, but whether long‐term disability progression varies across regions, and to what extent clinic‐level factors contribute, remains unclear. Methods We included 8260 people with relapsing‐onset MS from two nationwide cohorts linked to the Swedish MS registry. Primary analyses focused on incident cases ( n = 3160), the full cohort was used for complementary analyses. The primary exposure was healthcare region (Stockholm–Gotland reference). Outcomes were confirmed disability worsening (CDW) and time to EDSS 3 and EDSS 4. Cox models estimated region‐specific hazard ratios (HRs) with 95% confidence intervals (CI). Shared‐frailty models with clinic as a random effect accounted for within‐region clinic heterogeneity. Within‐region contrasts compared the three largest clinics in selected regions (anonymized). Two‐sided p values < 0.05 were considered statistically significant. Analyses were performed using SAS version 9.4. Results In incident cases, the Northern and Western regions showed consistently lower risks of CDW and of reaching EDSS 3 and EDSS 4 than Stockholm–Gotland. The South‐Eastern region had a lower risk for CDW (HR 0.74, 95% CI 0.59–0.94). After accounting for clinic‐level heterogeneity, regional contrasts attenuated and were no longer significant, as illustrated by the South‐Eastern region (HR 0.87, 95% CI 0.59–1.18). The full cohort showed similar geographic patterns. Within‐region clinic comparisons revealed substantial heterogeneity despite a shared regional context. Conclusions Apparent regional variation in long‐term MS disability progression in Sweden largely reflects between‐clinic differences rather than broad geographic gradients. Observed differences between clinics may reflect contributions from lifestyle‐related factors, clinic practices, and other unmeasured influences.
Hedström et al. (Thu,) studied this question.