Idiopathic granulomatous mastitis a mimicking disease: a case report

Introduction

Granulomatous mastitis is a rare benign inflammatory breast condition that was initially described by Kessler and Wolloch in 1972 (1). It is characterized by non-caseating granulomas and abscess formation resembling breast malignancy, especially inflammatory breast cancer, which often leads to challenges and delays in diagnosis (2,3). As in the case of many breast pathologies, non-white females of reproductive age are more commonly affected, with Hispanic women demonstrating a higher reported prevalence (3,4).

Although it is thought to be an autoimmune disease, other causes, such as Corynebacterium kroppenstedtii infection, have also been proposed (4,5). Risk factors identified among patients with granulomatous mastitis include oral contraceptive use, pregnancy, and breastfeeding (3,4).

Presentation is variable, but most women present with a palpable tender breast mass with no improvement after antibiotic therapy (5). In rare cases, patients may also present with systemic manifestations such as erythema nodosum or polyarthritis (6,7). When granulomatous mastitis is suspected, a core needle biopsy confirms the diagnosis, demonstrating multinucleated giant cells, plasma cells, polymorphonuclear leukocytes, lymphocytes, and occasionally sterile microabscesses (2,5).

There is no established gold-standard treatment for granulomatous mastitis, and management depends on clinical features and physician preference. Treatment strategies include observation, antibiotics, corticosteroids, immunomodulators, or surgery (3,8,9). Corticosteroid therapy has been associated with lower recurrence rates, while surgical excision is generally reserved for refractory cases (8,9). We present this article in accordance with the CARE reporting checklist (available at https://acr.amegroups.com/article/view/10.21037/acr-2026-0035/rc).

Case presentation

Twenty-five-year-old female, G1P1A0, with no significant past medical history, including no history of tuberculosis or malignancy, presented to St. Luke’s Episcopal Hospital with a right-sided breast mass with overlying erythematous changes of two months’ of onset.

She had initially presented to her primary care physician two weeks after the onset of symptoms, with a red, tender mass. She was prescribed antibiotic therapy for presumed breast abscess with no improvement in symptoms, which led to referral to breast surgeon for further evaluation. Patient reported a palpable right breast mass associated with pain and swelling, which had been slowly enlarging for a couple of weeks. She denied pain on palpation, nipple discharge, fever, chills, nausea, vomiting, or any personal or family history of malignancy. Upon further questioning, the patient presented with all three proposed risk factors for development of granulomatous mastitis; oral contraceptive use, recent pregnancy and breastfeeding, she had been breastfeeding for 3 years. Upon evaluation, there was erythema with associated skin changes in the upper half of the breast, findings also extended to the nipple-areola complex.

Right breast ultrasound revealed a right breast with dense parenchyma and hypoechoic regions at 10:00. Figure 1A demonstrates breast ultrasound findings. These findings revealed a right breast with ill-defined multifocal ectatic duct with intraductal debris in the right upper quadrant with associated intraductal echogenic component favoring debris and surrounding trabecular thickening that could represent focal mastitis. Bilateral magnetic resonance imaging (MRI) results (Figure 1B), ordered by the referring physician, described diffusely enhancing breast parenchyma with trabecular thickening, 3 cm × 3 cm, with no suspicious lesions observed.

Figure 1 Right breast lesions. (A) Breast ultrasound image. (B) MRI imaging of right breast. MRI, magnetic resonance imaging.

Core needle biopsy results confirmed diagnosis of granulomatous mastitis, and infectious etiologies were negative. Throughout course of disease diagnosis, the patient developed new symptoms of bilateral lower extremity swelling and bruise-like lesions, which were confirmed to be a known although rare presentation of erythema nodosum (Figure 2). Patient was started on systemic steroid treatment and sent for evaluation with rheumatologist, and medical oncologist.

Figure 2 Erythema nodosum.

Upon diagnosis of IGM, patient was admitted for commencement of intravenous (IV) steroids, after a short period of IV steroids patient was discharged home on prednisone 60 mg per oral daily, with attempts at tapering dose for a period of 8 months. Patient had only partial improvement in symptoms, and reported back with recurrent breast engorgement, swelling and pain, as well as various side effects from prolonged steroid use, which caused her distress and stopping treatment. Patient was presented with distinct treatment options, including alternative medical therapy, due to lack of access to certain alternative medical therapies and cost, the patient opted for a right total mastectomy. Preoperative findings shown in Figure 3.

Figure 3 Right breast with gross findings of periareolar erythema and scarring.

Gross intraoperative evaluation revealed extensive fibrous tissue and scarring around the lesion, with surrounding breast fat. As well as adhesions to adjacent tissue, likely due to chronic inflammation. Findings are demonstrated in Figure 4. Figure 5 demonstrates the excised lesion of the right breast with overlying skin changes. The patient had an uneventful post-operative period.

Figure 4 Gross intraoperative findings.

Figure 5 Excised right breast lesion breast lesion.

Pathology of right mastectomy, once again, confirmed granulomatous mastitis with no in situ or invasive malignancy identified. Acid-fast bacillus, Periodic-Acid Schiff, Gomori Methenamine Silver and Gram stains were used for evaluation of any bacterial or fungal organisms which were negative. The patient was advised to follow-up with a plastic surgeon for potential reconstruction once adequate wound healing.

All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Helsinki Declaration and its subsequent amendments. Written informed consent was obtained from the patient for publication of this case report and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Discussion

Idiopathic granulomatous mastitis (IGM) is a rare, benign, chronic inflammatory breast disease that frequently poses a diagnostic challenge due to its clinical and radiographic overlap with infectious mastitis and, less commonly, inflammatory breast carcinoma (5,10). This case highlights the complexity of diagnosis and management, emphasizing the importance of maintaining a high index of suspicion in young, reproductive-age women—particularly those of Hispanic descent, a population reported to have increased prevalence (3,4).

The patient’s initial presentation, managed as a presumed infectious abscess, reflects a common early clinical approach. However, the lack of response to antibiotic therapy appropriately prompted further evaluation. Histopathological examination ultimately established the diagnosis, demonstrating lobulocentric, non-caseating granulomatous inflammation without evidence of malignancy or infectious organisms (2,5). This underscores the critical role of tissue diagnosis in differentiating IGM from other etiologies, including tuberculosis, fungal infections, and breast carcinoma.

An additional notable feature in this case is the presence of erythema nodosum, a recognized but uncommon extra-mammary manifestation of IGM. Its occurrence supports the hypothesis of an underlying systemic inflammatory or autoimmune mechanism and has been described in association with more severe or recurrent disease courses (6,7). Erythema nodosum is thought to represent a delayed hypersensitivity reaction or immune complex-mediated process, further supporting the concept of IGM as an immune-mediated condition (7).

Clinically, the presence of erythema nodosum has been associated in some reports with more extensive or systemic disease involvement; however, its impact on overall prognosis remains uncertain (7). While it may correlate with increased inflammatory burden and, in some cases, a more prolonged or recurrent disease course, current evidence does not demonstrate a clear independent association with worse long-term outcomes (7).

The patient’s clinical profile—including recent pregnancy, breastfeeding, and oral contraceptive use—aligns with proposed hormonal and immune-mediated contributors to disease pathogenesis (3,4). Although Corynebacterium kroppenstedtii has been implicated in a subset of cases, no infectious organism was identified in this patient, supporting a diagnosis of idiopathic disease (5).

Imaging findings in IGM are typically non-specific but remain essential for excluding malignancy and guiding biopsy (10,11). In this context, core needle biopsy remains the diagnostic gold standard, allowing for definitive histopathological characterization and exclusion of alternative diagnoses (2,5).

Management of IGM remains controversial and is not standardized. Corticosteroids are widely used as first-line therapy in moderate to severe disease or in patients with systemic manifestations (8,9). In this case, although initial corticosteroid therapy resulted in partial symptomatic improvement, persistent disease activity and treatment-related adverse effects necessitated escalation of care. Surgical management, including wide local excision or mastectomy, is generally reserved for refractory or recurrent cases (9). The patient’s decision to proceed with mastectomy, while aggressive, was appropriate given the chronicity of symptoms, limited response to medical therapy, and her preference for definitive treatment and improved quality of life.

Limitations

The report describes only one patient, which limits generalizability and prevents statistical inference. Findings can’t establish causality or define best practice—only generate hypotheses or highlight rare presentations.

Conclusions

This case emphasizes several critical considerations in the management of IGM: the need for early biopsy in non-resolving breast lesions, the potential for systemic manifestations, and the importance of individualized treatment strategies (8,12). In young patients, particularly Hispanic women presenting with atypical or persistent breast inflammation, granulomatous mastitis should remain an important differential diagnosis (3,4). The lack of standardized treatment guidelines necessitates a multidisciplinary approach, involving breast surgeons, radiologists, pathologists, and rheumatologists to optimize patient outcomes (8,9).

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the CARE reporting checklist. Available at https://acr.amegroups.com/article/view/10.21037/acr-2026-0035/rc

Peer Review File: Available at https://acr.amegroups.com/article/view/10.21037/acr-2026-0035/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://acr.amegroups.com/article/view/10.21037/acr-2026-0035/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Helsinki Declaration and its subsequent amendments. Written informed consent was obtained from the patient for publication of this case report and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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