SUMMARY
Introduction. Multiple sclerosis (MS) phenotype transition, is a clinically important milestone with implications for prognosis and treatment. The objective of this study was to examine MS phenotype transitions and associated factors in Azerbaijan. Material and methods. A longitudinal analysis (2013–2022) included patients diagnosed with clinically isolated syndrome (CIS) and relapsing-remitting MS (RRMS) in Azerbaijan (67 and 1397 patients accordingly). Phenotype transition was defined as CIS→RRMS or RRMS→secondary progressive MS (SPMS). Statistical analyses were performed using the Pearson chi-square test and the Mann–Whitney U test. Associations were evaluated using univariable and multivariable binary logistic regression in a cohort with complete baseline and follow-up data (n=408). Results. During follow-up, 378 patients (25.8%) changed phenotype. CIS→RRMS occurred in 70.1% of CIS cases (47) and RRMS→SPMS in 23.7% of RRMS cases (331). Phenotype change was more common after CIS than after RRMS (p<0.001). Median time was shorter in CIS than RRMS (p<0.001). Overall, univariable analyses identified candidate predictors of phenotype transition for inclusion in the multivariable logistic regression model. In the multivariable model, 24-month disease-modifying therapy (DMT) adherence and disease duration ≤10 years were associated with lower odds of phenotype change (p<0.001). No relapse in the first year and absence of sensory symptoms were associated with higher odds (p<0.001 and p=0.010), whereas absence of speech disturbance was associated with lower odds (p=0.019). Conclusion. One quarter of patients transitioned between MS phenotypes, earlier after CIS. DMT adherence and selected baseline clinical features were independently associated with phenotype change, supporting risk-stratified follow-up and treatment optimization.
Keywords: multiple sclerosis, clinically isolated syndrome, relapsing-remitting multiple sclerosis, secondary progressive multiple sclerosis, phenotype transition, Azerbaijan

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