Baseline inability-to-feel severity is associated with fewer first-year days well in bipolar disorder: A STEP-BD analysis

Background Depressive symptoms are major determinants of outcome in bipolar disorder. We examined whether baseline anhedonia-related symptom severity was associated with subsequent clinical wellness. Methods We analyzed longitudinal data from the STEP-BD, a multicenter naturalistic effectiveness study of bipolar disorder. The primary predictor was baseline MADRS item 8 (“Inability to Feel”) score. The primary outcome was the first-year proportion of days well. Secondary outcomes were functioning (LRIFT) and quality of life (Q-LES-Q). Core models adjusted for baseline MADRS total excluding item 8, YMRS total, age, sex, bipolar II diagnosis, and age-at-onset category. Sensitivity analyses included multiple imputation, treatment-adjusted models, categorical item 8 specifications, nonlinearity testing, and negative binomial regression. Results The primary analytic sample included 2576 participants. Higher baseline MADRS item 8 scores were associated with a lower first-year proportion of days well (p < 0.001; standardized β = −0.088; incremental R2 = 0.004 over a model including all other covariates). The adjusted predicted difference between scores 0–3 corresponded to approximately 18 fewer days well per year. The association was robust across multiple sensitivity analyses including multiple imputation, treatment-adjusted models, and categorical specifications. It did not significantly predict follow-up LRIFT or Q-LES-Q. Conclusion Baseline inability to feel was modestly but consistently associated with fewer first-year days well in bipolar disorder, independent of overall depressive severity and major clinical covariates. The effect size was small and did not extend to functioning or quality of life after accounting for baseline levels of those outcomes.