This study was designed with the aim to describe the clinical phenotype, serological and radiological profiles and treatment response to rituximab in patients with idiopathic inflammatory myositis (IIM) in a Pakistani population.

Idiopathic inflammatory myopathies are a group of autoimmune disorders characterized by symptoms of progressive muscle weakness and extra-muscular manifestations. Pulmonary involvement in IIM presents as interstitial lung disease (ILD) and is associated with high prevalence and mortality rates. Recent studies have highlighted the role of serum autoantibodies in predicting and monitoring disease progression in IIM.

In this retrospective study, we enrolled 43 patients with anti-myositis panel-confirmed IIM who presented to the neurology and/or pulmonology outpatient clinics in our tertiary care center. Demographic, clinical, laboratory, and radiographic data were extracted from medical records.

15 (34.9%) patients had IIM-ILD. Most IIM-ILD cases (73.3%) were identified at baseline. Patients with ILD were significantly more likely to present with respiratory symptoms (dyspnea, p = 0.0014; cough, p < 0.001). Anti-synthetase syndrome was the most frequent IIM subtype and was associated with ILD development (p = 0.023). Nonspecific interstitial pneumonia was the most common radiologic pattern in ILD patients. The most frequently detected myositis-specific antibody was anti-Ro52, present in 23.3% of the overall cohort. Rituximab led to comparable improvement rates between IIM-ILD and IIM-only patients despite significantly fewer doses in the IIM-ILD group (p = 0.009). Within the IIM-ILD subgroup, younger age at onset (p = 0.031) and anti-Ro52 positivity (60% vs 10%, p = 0.077) were more frequent among those requiring rituximab.

Treatment practices in Pakistan were found to be consistent with global patterns. The findings of this study underscore the importance of early screening, antibody profiling, and individualized treatment regimens, while also generating hypothesis for future prospective studies to further define predictive markers and optimize ILD management in IIM patients.