Performance of IMACS Malignancy Risk Stratification in Idiopathic Inflammatory Myopathies: A Single-centre Retrospective Cohort Study from India

Abstract

Background: Idiopathic inflammatory myopathies (IIMs) carry an increased malignancy risk. Although the International Myositis Assessment and Clinical Studies Group (IMACS) has proposed guidelines to screen malignancies, their applicability across populations remains uncertain. In this study, we analysed risk factors for malignancies in IIM using the IMACS guidelines. Methods: Clinical, serological and malignancy-related data from a single-centre cohort of patients with definite IIM (≥90% probability by European Alliance of Associations for Rheumatology [EULAR]/American College of Rheumatology [ACR]criteria) were analysed for malignancy risk factors. Those patients with incomplete screening data for malignancy were excluded. Associations between IMACS predefined malignancy risk factors and malignancy were assessed. Results: Among 111 patients with definite IIM, six (5.4%) had malignancy. Median age at IIM onset was significantly higher in patients with malignancy (50.5 vs. 39 years; P = .03), while median creatine phosphokinase levels were significantly lower (99 vs. 710 U/L; P = .01). Dermatomyositis (DM) was significantly associated with malignancy (Odds Ratio [OR] = 4.31, 95% Confidence Interval [CI] = 1.40–13.27; P = .02). Based on IMACS risk stratification, five of six malignancy patients were classified as high-risk and one as intermediate risk. The presence of IMACS high-risk features demonstrated a sensitivity of 83%, specificity of 58% and a negative predictive value of 98.4% for identifying malignancy. Conclusion: Malignancy occurred in 5.4% of IIM patients in this Indian cohort, with older age and DM being more frequent in the malignancy group. IMACS risk stratification showed high sensitivity and excellent negative predictive value for malignancy detection, supporting its utility in malignancy screening among patients with IIM.