Case Presentation: A 31-year-old female gravida 2 para 2 with past medical history notable for iron-deficiency anemia presented to the hospital with complaints of fever, lower extremity rash, and multiple breast masses. The patient described having bilateral breast firmness and tenderness for 3 weeks, which was being worked up as an outpatient. The patient had obtained a breast ultrasound, which showed multiple hypoechoic nodules bilaterally, and a mammogram, which was negative for malignancy. The patient also endorsed a 1-week history of lower extremity edema and erythema. On exam, she was febrile to 102.7°F and tachycardic to 110 beats/minute. A firm breast mass was palpable on the left upper inner quadrant whereas scattered firm nodules were noted on the right breast. The patient also had bilateral axillary and inguinal lymphadenopathy in addition to erythematous, tender nodules on her bilateral shins. Labs were notable for white blood cell count of 12,640 cells/µL, hemoglobin of 10.3 g/dL, erythrocyte sedimentation rate of 77 mm/hr, C-reactive protein of 58.7 mg/L, and serum immunoglobulin E level of 265 kU/L. Serum C3 and C4 levels were within normal limits. She tested negative for antinuclear, antineutrophil cytoplasmic, and extractable nuclear antigen antibodies. The patient was started on broad-spectrum antibiotics. A skin biopsy confirmed erythema nodosum while a repeat ultrasound revealed a left breast abscess. A drain was placed, which evacuated purulent fluid. Tissue was taken for culture and biopsy; a gram stain, acid-fast bacilli smear and culture, and Grocott methenamine silver stain were all negative. The breast biopsy revealed benign breast parenchyma with acute and chronic inflammation in addition to multiple noncaseating granulomas containing multinucleated giant cells. The patient was diagnosed with idiopathic granulomatous mastitis (IGM). Antibiotics were ultimately stopped and she was discharged on prednisone.

Discussion: IGM is a rare, benign breast inflammatory disorder affecting childbearing women with a history of breastfeeding. Median age of onset is 30. It is estimated to occur in less than 0.5 percent of the US population. Hypothesized trigger factors include pregnancy, lactation, autoimmunity, and hyperprolactinemia. Patients often present with an enlarging breast mass with signs of inflammatory changes, such as erythema and tenderness. With no specific radiographic features, it can often mimic a breast abscess or malignancy. Ultrasonography usually shows irregular, hypoechoic masses whereas the most common finding in mammography is focal symmetry without distortions or microcalcifications. Due to these nonspecific findings, diagnosis may be delayed. Core needle biopsy is used for definitive diagnosis. Histology reveals multiple noncaseating epithelioid granulomas, often with multinucleated giant cells. Left untreated, IGM may resolve in 1-2 years. If palliation of symptoms is warranted, multiple treatment options exist, albeit with no standard of care. The most common solution used is wide surgical excision, with or without concomitant corticosteroid therapy. Abscess drainage and expectant management are also utilized. Due to wide variability in treatments offered, the rate of recurrence is estimated to be up to 50 percent.

Conclusions: IGM is a rare breast inflammatory disease that may be difficult to distinguish from malignancy. More research is needed to identify the optimal treatment options to be offered for these patients.