Pediatric traumatic brain injury and early age multiple sclerosis in Finland: A nationwide register-based cohort study.

Objective: Examine the link between pediatric traumatic brain injury (pTBI) and early-onset multiple sclerosis in Finland.

Methods: Conducted nationwide register study (1998-2018) with 28,750 pTBI patients (< 18) and 38,399 pediatric references with extremity fractures. Multiple sclerosis diagnoses from Finnish Social Insurance Institution. Employed Kaplan-Meier and multivariable Cox regression for probability assessment, results presented with 95% CI.

Results: Of 66 post-traumatic multiple sclerosis cases, 30 (0.10%) had pTBI, and 36 (0.09%) were in the reference group. Cumulative incidence rates (CIR) in the first 10 years were 46.5 per 100,000 (pTBI) and 33.1 per 100,000 (reference). Hazard ratio (HR) for pTBI was 1.10 (95% CI: 0.56-1.48).Stratified by gender, women's CIR was 197.9 per 100,000 (pTBI) and 167.0 per 100,000 (reference) after 15 years. For men, CIR was 44.6 per 100,000 (pTBI) and 34.7 per 100,000 (reference). In the initial 3 years, HR for female pTBI was 1.75 (95% CI: 0.05-6.32), and between years 3 and 20, it was 1.08 (95% CI: 0.51-1.67). For male patients, HR was 1.74 (95% CI: 0.69-4.39).

Significance: We did not find evidence of an association between pTBI and early-onset multiple sclerosis 20 years post-initial trauma.