Case Report: Idiopathic Granulomatous Mastitis in a 39-Year-Old Female

Summary: Background: Idiopathic granulomatous mastitis (IGM) is a benign breast condition characterized by localized granulomatous inflammation. The exact cause is unclear, but autoimmune disease, infectious disease, and hormonal disruption are suggested triggers. Idiopathic IGM is more common in women of childbearing age, women taking oral contraceptive pills, and women in the peripartum period or who are breastfeeding. There is currently a paucity of information regarding the preferred treatment method for IGM. In this report, we describe a case of IGM with significant improvement on methotrexate. Through this report, we hope to improve diagnostic accuracy and optimize treatment outcomes for patients with IGM. Case Presentation: A 39-year-old Hispanic female with no significant past medical history presented with worsening right breast pain and skin erythema starting in late 2023. She is a former smoker of 5 pack-years who quit in 2012. She was seen in multiple urgent care clinics over the course of one month and each time, she was treated for bacterial mastitis with oral antibiotics but without any improvement. The patient began experiencing nipple retraction and worsening erythema with intractable breast pain. She presented to an emergency department and was noted to have extensive erythema of the right breast with skin retraction (Figure 1). A workup for infectious mastitis and malignancy was performed. Breast ultrasound revealed a 3.7 cm irregular retro-areolar mass in the right breast. Core needle biopsy showed spongiotic dermatitis with neutrophils, eosinophils, and underlying fibrosis with perivascular and peri adnexal chronic inflammation. Incisional biopsy showed fibroadipose tissue with acute and chronic inflammation. Fat necrosis with abundant histiocytes was noted, but no signs of malignancy (Figure 2). The patient was diagnosed with IGM and given prednisone 20 mg daily and referred to our rheumatology clinic. In the interim, she experienced several flares of pain with drainage from the biopsy site. Subsequently, oral methotrexate was started with rapid improvement of her skin lesions, and she was able to successfully taper the prednisone. (Figure 1). Tests for ACE, Vitamin D 1,25-OH, ANCA, QuantiFERON TB test, prolactin levels and a chest X-Ray were all normal. Discussion: Diagnosing IGM can be challenging, as it can mimic the nipple retraction and suspensory ligament infiltration of breast carcinoma. Additionally, mammography of IGM can be suggestive of malignancy. Many patients are initially misdiagnosed and undergo unnecessary surgical procedures. Therefore, it is crucial to exclude other infectious granulomatous etiologies before making a diagnosis. IGM is typically a tender breast mass with multiple foci in one breast but may also present bilaterally. It may also present with abscesses and overlying skin ulceration. A higher incidence of IGM is seen in women from Southeast Asia in the Middle east, although in the US, the highest incidence is in Hispanic women. MRI, ultrasound, and mammography have limited utility in diagnosis, as they may show nonspecific findings similar to malignancy. Definitive diagnosis is established with core needle biopsy showing non-necrotizing granulomas with epithelioid histiocytes, multinucleated giant cells, and predominantly neutrophilic background. Non-caseating granulomas are not seen in all patients, but epithelioid histiocytes are a consistent finding. Some authors have suggested their presence should be diagnostic of IGM. The management of IGM involves a combination of medical and surgical approaches. However, in some cases, it may be self-limited with supportive care. Corticosteroids and MTX are the mainstay of treatment. However, surgical resection may be necessary in some severe cases. Recurrence rates and response to treatment can vary, making the clinical course of the disease unpredictable. Conclusion: IGM is a rare inflammatory condition of unknown etiology characterized by non-caseating granulomas in breast tissue. Diagnosis can be complicated by its similarity to breast carcinoma, which may delay proper treatment. MTX and prednisone appear to be reliable and effective combination for treating severe or refractory cases of IGM. References (not included to reduce character count)