Nailfold Capillaroscopy Changes in Patients with Idiopathic Inflammatory Myopathies

Background/Objectives: Idiopathic inflammatory myopathies (IIMs) are rare autoimmune disorders characterized by progressive proximal muscle weakness and varying extra-muscular manifestations. The latest 2017 EULAR/ACR criteria classify them into subgroups. This study aims to evaluate the role of nailfold capillaroscopy (NFC) as a diagnostic and prognostic tool in IIMs by comparing capillaroscopic patterns across different IIM subtypes. Methods: We conducted an observational, cross-sectional study at the Institute of Rheumatology in Belgrade, analyzing 90 patients diagnosed with IIMs per the 2017 EULAR/ACR criteria. Patients were categorized into dermatomyositis (DM) (n = 37), polymyositis (PM) (n = 35), amyopathic dermatomyositis (ADM) (n = 13), and juvenile dermatomyositis (JDM) (n = 5). A control group of 35 patients with primary Raynaud's phenomenon was also included. NFC findings, clinical manifestations, and laboratory data were compared across the groups. Results: In DM, 81.9% exhibited a scleroderma capillaroscopic pattern, which was also present in 76.9% of ADM patients. In PM, the most common pattern was nonspecific changes (48.6%). JDM patients showed a high prevalence of scleroderma changes (n = 4 (80%)). Scleroderma patterns correlated with Gottron's papules, heliotrope rash, periungual erythema, Raynaud's phenomenon, and interstitial lung disease (ILD). No significant differences were found in laboratory parameters across capillaroscopic groups, except for a higher prevalence of anti-Jo1 antibodies in patients with nonspecific capillaroscopic changes. Conclusions: NFC is a valuable tool for differentiating IIM subtypes and correlating clinical manifestations with specific capillaroscopic patterns. The high prevalence of scleroderma changes in DM and ADM suggests their potential as a diagnostic and prognostic marker in IIMs. Further research with larger cohorts is warranted to validate these findings.