Interstitial Lung Disease in Dermatomyositis and Polymyositis in Patients from Saudi Arabia: A Single Tertiary Center Retrospective Report

Background: Interstitial lung disease (ILD) is a major extra-muscular manifestation of dermatomyositis (DM) and polymyositis (PM), yet data from Middle Eastern populations remain sparse. We aimed to characterize radiologic ILD patterns, severity, clinical–serologic correlates, and treatment usage among Saudi patients with PM/DM-ILD managed at a tertiary center. Methods: We conducted a retrospective cohort study (2006–2022) at a single tertiary hospital in Riyadh, Saudi Arabia. Adult patients (≥18 years) with PM/DM by 2017 ACR/EULAR classification were re-adjudicated, and ILD was confirmed by high-resolution CT (HRCT) after blinded re-review by a thoracic radiologist. ILD patterns followed ATS/ERS categories (NSIP, UIP, OP, RB-ILD, unclassifiable). Severity was treated separately from pattern and operationalized as “mild” if HRCT parenchymal involvement was <20% or, when imaging was equivocal, if FVC ≥80% predicted. Demographics, clinical features, standard serologies, pulmonary function tests (PFTs), echocardiography, and treatments were abstracted using a standardized form with double-entry checks. Analyses were descriptive and exploratory; between-group comparisons were limited to subgroups with n≥5 and adjusted for multiple testing (Holm). Results: Thirty-five patients met criteria (80% female; DM 60%, PM 40%). On HRCT rereview, NSIP was the most frequent pattern (37.1%, 13/35), followed by unclassifiable (14.3%, 5/35), UIP (5.7%, 2/35), RB-ILD (2.9%, 1/35), and OP (2.9%, 1/35). In parallel, severity was mild in 37.1% (13/35) across patterns. ILD timing relative to myositis was PM/DM-preceding in 48.6%, concomitant in 31.4%, and ILD-preceding in 20%. Exertional dyspnea (74.3%) and non-productive cough (62.9%) were frequent; heliotrope rash and Gottron papules each occurred in 34.3%. ANA was positive in 82.9%; anti-Jo-1 in 34.3%. FVC (mean ± SD) approximated 71% predicted overall; DLCO ~90% predicted where available. As pre-specified, no inferential tests were performed for subgroups with n<5 (UIP, RB-ILD, OP), and signals from small cells were treated descriptively only. Glucocorticoids were universally used; 77.1% were maintained at ≤7.5 mg/day. Mycophenolate mofetil (54.3%) and rituximab (48.6%) were the most common steroid-sparing agents; azathioprine (40%), methotrexate (34.3%), and IVIG (25.7%) were also used; antifibrotics were prescribed in 11.4%. Conclusion: In this Saudi tertiary-care cohort, NSIP predominated as the ILD pattern, while mild severity at presentation was common but distinct from pattern. The dataset underscores heterogeneity in serology and treatment and highlights the need for standardized radiologic severity grading, prospective PFT capture, and multicenter registries to refine prognosis and guide therapy in regional PM/DM-ILD.