Different age, different phenotype: a comparative analysis of juvenile and adult-onset dermatomyositis from a tertiary center

OBJECTIVES: To evaluate age-related differences in clinical features, serological profiles, diagnostic approaches, treatment strategies, and outcomes among juvenile- and adult-onset dermatomyositis (JDM and AoDM) patients managed at the same tertiary referral center. METHODS: This retrospective cohort included 180 patients with dermatomyositis meeting the 2017 EULAR/ACR classification criteria and followed between 1995 and 2025 at the pediatric and adult rheumatology clinics. Diagnosis before 16 years was classified as JDM. RESULTS: Among 180 patients, 86 had JDM and 94 had AoDM. A bimodal age distribution was observed, with peaks at 6.8 and 45.7 years. 67.8% were female; median follow-up was 5.9 years. Muscle weakness (86.7%) and cutaneous involvement (98.3%) were most common findings. Calcinosis was frequent in JDM (33%) but rare in adults (one case). Both calcinosis and arthritis were significantly associated with JDM (p = 0.007 and p = 0.049). Anti-NXP2 was the leading JDM autoantibody (31.4%, 11/35), whereas anti-synthetase antibodies (34.6%, 9/26) in AoDM. Glucocorticoids were given to both groups; however, steroid-free (40.3% vs 89.6%, p = 0.020) and drug-free remission rates (40.3% vs 16.7%, p = 0.020) were higher in JDM. Malignancy-associated dermatomyositis occurred only in AoDM (n = 25, 26.6%). Age at diagnosis was independently associated with both mortality (OR 1.07 per year, 95% CI 1.02-1.11) and malignancy (OR 1.05 per year, 95% CI 1.00-1.10). CONCLUSION: JDM and AoDM are not merely age-defined variants but display distinct clinical, serological, and prognostic profiles. JDM shows calcinosis and better remission and survival, whereas AoDM is strongly associated with malignancy and higher mortality burden, highlighting the need for age‑tailored diagnostic and management strategies.