Treatment of idiopathic granulomatous mastitis: a retrospective case series.

Idiopathic granulomatous mastitis (IGM) is a rare inflammatory disease of the breast. Various clinical management approaches have been described, but their efficacy and optimal sequential order remain uncertain. We describe the first Canadian cohort of patients with IGM, discuss treatment outcomes and outline a practical management approach. This retrospective study included patients diagnosed with biopsy-confirmed IGM between 2014 and 2023, aged over 18 years. Based on a scoping review of the literature, a diagnostic and management approach was developed, and we present here the disease course and outcomes using this approach. 22 females were included, with a mean age of 40 (24-65) years, mostly presenting with a breast lump (n =22, 100%) and breast pain (n = 15, 68%). Mean rheumatology follow-up was 28.7 months (range 3-79). Mean time from first symptom to diagnosis was 3.5 months (range 1-13). Corynebacterium kroppenstedtii was found in 8 patients. Treatment including lipophilic antibiotics, corticosteroids and disease modifying anti-rheumatic drugs (DMARDs), led to complete remission in 95% of patients, in a mean time of 11.6 months (range 1-36), and relapse in only 1 patient. 11 patients required DMARDs (50%), most commonly methotrexate (n=9). We highlight the variable severity of IGM and the benefits of a severity-based treatment approach. A diligent evaluation and work-up is essential to manage IGM. The proposed severity-based management approach with medical treatment and less aggressive surgical intervention led to complete remission in 95%.