LAUSR

A 65-year-old post-menopausal woman presented to the breast clinic with 6 months’ history of an asymptomatic lump at the 2 o’clock position of her left breast. She proceeded to a mammogram and ultrasound, which showed a heterogeneous echogenic mass; and a core biopsy, which showed granulomatous inflammation. Microbial studies were negative. A diagnosis of granulomatous mastitis was made, and she was trialed on medical management with 6 weeks of oral doxycycline. At follow-up, the original lesion had progressed to a painful cratered ulcer, and a further lump was noted at the 1 o’clock position (Fig. 1a). Repeat mammogram (Fig. 1b), ultrasound and core biopsies for histology (Fig. 2a) and tissue cultures yielded similar findings of granulomatous inflammation without evidence of infection, atypia or malignancy. Upon referral to dermatology, a full systems enquiry noted malaise, reduced appetite, unintentional weight loss, together with subcutaneous nodules of the lower abdomen and recent onset nonproductive cough. Investigations for underlying granulomatous disorders revealed positive c-ANCA/proteinase-3 antibody, lobular panniculitis with neutrophilic micro-abscesses and vasculitis on incisional biopsy of the abdominal nodules (Fig. 2b), and bilateral pancoast lesions representing pulmonary vasculitis on computed tomography of the chest (Fig. 3). A diagnosis of granulomatosis with polyangiitis (GPA), masquerading as granulomatous mastitis, was made. Idiopathic granulomatous mastitis is an increasingly recognized, albeit rare, entity that can mimic breast malignancies and abscesses. The pathogenesis is poorly understood, currently conceptualized as an autoimmune reaction to milk proteins within interstitial breast tissue. Supporting this hypothesis, it presents as a mass with variable pain, erythema or discharge, typically in women of child-bearing age who have a recent history of pregnancy and lactation. The histologic pattern of lobulocentric granulomatous inflammation can also be observed in malignancies, infections and