Clinicopathological and serological spectrum of idiopathic inflammatory myopathies: Experience from a neuromuscular referral center in Cyprus

Background The classification of idiopathic inflammatory myopathies (IIMs) has evolved substantially with the identification of myositis-specific autoantibodies (MSAs). However, how contemporary classification frameworks are applied in routine clinical practice remains variable. This study provides a clinicopathological and serological characterization of IIMs from a national neuromuscular referral center in Cyprus. Methods We conducted a retrospective, single-center cohort study of adult patients diagnosed with IIM between 2007 and 2025. Patients were classified using a clinicopathological and serological approach into dermatomyositis (DM), immune-mediated necrotizing myopathy (IMNM), antisynthetase syndrome (ASyS), overlap myositis (OM), inclusion body myositis (IBM), and polymyositis (PM), with the 2017 EULAR/ACR criteria used as a reference framework and historical diagnoses re-evaluated. Results 36 patients were included. Final subtype distribution: IMNM in 14 patients (39%), DM in 7 (19%), IBM in 4 (11%), OM in 5 (14%), ASyS in 3 (8%), PM in 2 (6%). Only one patient remained non-classifiable. Autoantibody testing was performed in 26/36 patients; MSAs were detected in 19/26 tested (73%; 53% of the total cohort), most commonly anti-HMGCR, while anti-NT5C1A antibodies were detected in three additional patients. Muscle biopsy was performed in the majority of patients, reflecting historical diagnostic practices. Conclusion This study demonstrates real-world application of contemporary IIM classification, enabling accurate disease subtyping with direct implications for malignancy surveillance and interstitial lung disease monitoring, as well as reclassification of cases, most notably those previously labelled as PM. The findings further underscore the role of muscle biopsy, particularly when serology is negative, discordant, or unavailable.