Background: Anti-melanoma differentiation-associated gene 5 (anti-MDA5) positive dermatomyositis is a distinct subset of idiopathic inflammatory myopathies (IIMs), often associated with unique cutaneous features and interstitial lung disease (ILD). While East Asian cohorts frequently report high mortality due to rapidly progressive ILD (RP-ILD), data regarding Central and Eastern European populations remain scarce. Methods: We conducted a retrospective multicenter study of anti-MDA5 positive Caucasian patients managed at four Hungarian rheumatology centers between 2020 and 2025. Demographic, clinical, serological, and radiological data were analyzed. Antibody profiling was performed using a standardized 16-antigen immunoblot assay. Results: Anti-MDA5 positivity was confirmed in 24 out of 742 patients (3.23%) treated in the four centers. The median age at diagnosis was 49.5 years (range: 24–81). Classic dermatomyositis was the predominant clinical phenotype (75%), followed by clinically amyopathic dermatomyositis (CADM) (12.5%) and polymyositis (12.5%). ILD was identified in 58.3% of patients, presenting with organizing pneumonia (OP), non-specific interstitial pneumonia (NSIP), and usual interstitial pneumonia (UIP) patterns. At diagnosis, median creatine kinase (CK) (193.5 U/L) and C-reactive protein (CRP) (4.24 mg/L) levels remained low even in the ILD group, whereas lactate dehydrogenase (LDH) was elevated in 91.7% of the cohort. Anti-Ro52 positivity (45.8% overall) emerged as a notable predictor of ILD (odds ratio [OR]: 22.5, 95% confidence interval [CI]: 2.10–240.48; p = 0.0045), being present in 71.4% of affected patients. RP-ILD occurred in two patients (8.3%). Therapeutic management followed an early, aggressive strategy, frequently utilizing cyclophosphamide (45.8%) and methotrexate (37.5%), with Janus kinase (JAK) inhibitors or rituximab employed in refractory cases. Overall disease-specific survival was 100% during the study period (median follow-up: 72.0 months); no mortality was directly attributable to IIM-related complications. Conclusions: Our study demonstrates that anti-MDA5 positive dermatomyositis in a Hungarian cohort is characterized by heterogeneous manifestations and a significant association between anti-Ro52 and ILD. The observed dissociation between low CK/CRP and elevated LDH underscores the necessity for a high index of suspicion, with LDH serving as a superior marker for disease activity. While ILD presents a significant risk, early and intensive multi-modal intervention may yield superior survival outcomes in European patients compared to the historical mortality rates reported in Asian cohorts.

Anti-melanoma differentiation-associated gene 5 (anti-MDA5) antibodies are critical biomarkers in myositis, associated with distinct clinical features and prognosis. This study aimed to evaluate the proportion of anti-MDA5 positivity and compare the diagnostic performance of local immunoblotting (IB) with gold-standard immunoprecipitation (IP). We performed a retrospective analysis of 3272 physician-requested anti-MDA5 IB determinations over a five-year period (2019–2023). A subsequent exploratory pilot study of ten Hungarian patients with myositis was conducted to compare IB results with radiolabeled protein IP. Confirmatory in-house enzyme-linked immunosorbent assay (ELISA) was used to distinguish between 140 kDa bands (anti-MDA5 vs. anti-NXP2). Indirect immunofluorescence (IIF) on HEp-2 cells was also evaluated. In the retrospective cohort, 3.7% (n = 121) of samples were non-negative. Among 64 borderline patients, only one (1.6%) had a definitive diagnosis of dermatomyositis (DM). Conversely, the proportion of confirmed myositis cases was notably higher among patients with strong positive IB results. In our exploratory cross-sectional pilot study, complete concordance between the two assays was observed for negative and strong positive results. Discrepancies were noted in borderline and weak positivity ranges, where anti-MDA5 was not detected by IP; instead, alternative autoantibodies were identified. The three IP-confirmed MDA5 positive samples were all validated by ELISA. The characteristic IIF cytoplasmic staining was identifiable in 2 out of 10 cases (20%). In our cohort, borderline IB cases were frequently potential false positives, highlighting the need for careful clinical evaluation. Borderline and weak results require clinical correlation or confirmatory testing to avoid misdiagnosis.