A Prospective Study of Clinical Presentation, Radiological Findings, and Treatment Outcomes in Patients With Idiopathic Granulomatous Mastitis at a Single Center

Background: Idiopathic granulomatous mastitis (IGM) is a benign, inflammatory breast disease that clinically and radiologically mimics malignancy and infection, posing diagnostic and therapeutic challenges - particularly in tuberculosis (TB)-endemic settings. Evidence on standardized, medical-first strategies in Indian cohorts remains limited. Objective: To describe the clinical presentation, radiological features, histopathology, and treatment outcomes of IGM managed with corticosteroids, methotrexate (MTX), and hydroxychloroquine (HCQ) at a single center. Methods: In this prospective cohort (October 2016-June 2025), consecutive patients with core biopsy-confirmed IGM were enrolled after exclusion of infection (including TB polymerase chain reaction (PCR)/culture), autoimmune diseases, and systemic granulomatous disorders. Clinical, laboratory, and multimodality imaging (ultrasonography (USG) and mammography for all; MRI selectively) were recorded. Patients received tapering oral corticosteroids (0.5 mg/kg/day) and upfront MTX (10-15 mg/week); HCQ was added in selected cases. Follow-up included monthly, then three‑monthly assessments with serial labs and imaging. Outcomes were analyzed descriptively. Results: We identified 110 women (mean age 37.7 ± 7.4 years). Common presentations were breast swelling (41.8%, n=46), palpable lump (30.9%, n=34), pain (22.7%, n=25), and discharge (8.2%, n=9). Imaging typically showed ill‑defined, heterogeneous hypoechoic masses with frequent abscesses, sinus tracts, and reactive axillary nodes; Breast Imaging Reporting and Data System (BI‑RADS) categories were 2 (n=15), 3 (n=29), and 4A-4C (n=66). Histopathology most often demonstrated IGM (48.6%, n=54) and cystic neutrophilic granulomatous mastitis (CNGM; 23.9%, n=26). All patients received corticosteroids plus MTX; most did not require surgery. By 12 months, 76% (n=76) showed clinical improvement on MTX monotherapy; among 100 patients with 12‑month data, 38% (n=38) had no evidence of disease, 56% (n=56) continued treatment, 7% (n=7) were lost to follow‑up, and 9% (n=9) had no improvement. At 18 months, overall, recurrence was documented in nine patients; no clinically significant adverse events were recorded. Median treatment duration was 18-24 months. Conclusions: In this Indian single‑center prospective cohort, a medical‑first strategy using corticosteroids with early MTX achieved high rates of improvement, low surgical utilization, and acceptable recurrence. Multimodality imaging often necessitated biopsy due to frequent BI‑RADS 4 assignments. These findings support conservative, immunomodulator‑based management and underscore the need for standardized protocols and multicenter prospective validation.