Recurrent Myocarditis in Young Adults: Identifying High-Risk Phenotypes and the Protective Effect of Adequate Colchicine Therapy.

Background and Objectives: Recurrent myocarditis confers a significant prognostic burden yet lacks validated predictive markers to guide risk stratification. This study aimed to identify independent clinical, electrocardiographic, and cardiac magnetic resonance (CMR) determinants of recurrence at a median of 7 days (IQR: 3-14) after the index event in young adults with acute myocarditis and to evaluate the role of colchicine therapy duration in modulating recurrence risk. Materials and Methods: This retrospective observational cohort study enrolled 162 patients admitted with a diagnosis of acute myocarditis to a tertiary cardiology center between January 2014 and January 2024. Diagnosis was established according to ICD-10 criteria with confirmation by CMR. The primary endpoint was recurrent myocarditis at two-year follow-up. Independent predictors were delineated through binary logistic regression and time-to-event analyses using multivariate Cox proportional hazards modeling. Results: The two-year recurrence rate was 12.3%, with a median time to recurrence of 13.5 months. Time of colchicine use, ST-segment depression on the admission electrocardiogram (OR 14.469, 95%CI 2.416-86.673; p = 0.003), and late gadolinium enhancement (LGE) on CMR (OR 10.362, 95%CI 1.614-66.549; p = 0.014) emerged as independent predictors of recurrence. Colchicine therapy sustained for a minimum of three months was independently associated with a markedly reduced recurrence risk (OR = 0.295, 95%CI = 0.098-0.891; p = 0.030). Cox regression corroborated these associations, demonstrating substantially elevated hazard ratios for ST depression (HR = 10.729, 95%CI = 2.201-52.298; p = 0.003) and LGE (HR = 8.064, 95%CI = 2.036-31.942; p = 0.003), with a protective effect of adequate colchicine duration (HR = 8.577 for treatment cessation; p = 0.025). A multisegmental LGE pattern and index episode onset during the winter months were additionally associated with recurrence. Conclusions: ST-segment depression on admission electrocardiography and CMR-detected LGE may represent potent, independent predictors of myocarditis recurrence. Adequate colchicine duration of at least three months may attenuate recurrence risk, underscoring the critical importance of optimizing anti-inflammatory therapy duration and integrating electrocardiographic and imaging phenotyping into personalized long-term surveillance strategies.