Abstract
BACKGROUND: Idiopathic granulomatous lobular mastitis is a rare chronic inflammatory disease of the breast. Idiopathic granulomatous lobular mastitis is a benign entity of unknown etiology occurring mainly in women of reproductive age that can clinically and radiologically mimic breast carcinoma, making diagnosis both challenging and delayed. CASE PRESENTATION: A 38-year-old otherwise healthy Indonesian female patient presented with a painful and enlarging mass of the left breast with overlying erythema that was unresponsive to antibiotic therapy. Regional lymphadenopathy and mammography findings were concerning for inflammatory cancer of the breast. The patient eventually developed erythema nodosum and polyarthralgia, coupled with histopathology confirmation, leading to a diagnosis of idiopathic granulomatous lobular mastitis. Complete symptom resolution was achieved using immunosuppressive treatment with systemic steroids and localized intralesional steroids. The patient remained asymptomatic with no disease relapse at 3-year follow-up using a conservative approach to treating idiopathic granulomatous lobular mastitis, with high patient satisfaction. CONCLUSION: Idiopathic granulomatous lobular mastitis is a rare and diagnostically challenging condition that clinically and radiologically mimics breast carcinoma. A high index of clinical suspicion is required for diagnosis. Histopathology is recommended over clinical imaging studies if idiopathic granulomatous lobular mastitis or breast cancer are suspected. Due to the rarity of this condition, this case report provides valuable insight into the diagnostic approach, differential diagnosis, associated radiological and histopathological findings, and treatment options, and also serves as a reference for successful treatment of idiopathic granulomatous lobular mastitis using conservative local and systemic immunosuppressive therapies with no clinical relapse for 3 years. Multidisciplinary approach is needed to prevent diagnostic delay and provide optimal therapeutic management and outcome.