Granulomatous breast mastitis in pregnancy secondary to Mycobacterium avium complex: a case report

Granulomatous breast mastitis is a rare inflammatory condition that can mimic both infectious mastitis and breast malignancy. Its occurrence during pregnancy is uncommon and poses significant diagnostic and therapeutic challenges. Mycobacterium avium complex (MAC) has not previously been reported as a causative agent in an immunocompetent pregnant patient.

A 42-year-old immunocompetent woman, gravida 7 para 6, presented at 4 weeks' gestation with progressive left breast pain, swelling, and erythema. Sequential antibiotic courses failed to produce sustained improvement, and the condition progressed to recurrent abscess formation requiring multiple aspirations and two formal incision-and-drainage procedures. An initial culture grew Klebsiella oxytoca; however, the absence of clinical response and the histopathological finding of non-caseating granulomatous inflammation prompted extended microbiological workup. Mycobacterial culture confirmed MAC in the third trimester. Tuberculosis was excluded through negative interferon-gamma release assay, polymerase chain reaction, and acid-fast bacillus smear. Systemic corticosteroids and triple antimycobacterial therapy were withheld throughout pregnancy; the patient was managed conservatively with drainage and supportive antibiotics. Following delivery, an 18-month course of rifampin, ethambutol, and azithromycin achieved complete clinical and radiological resolution.

This case highlights the importance of maintaining a high index of suspicion for atypical mycobacterial pathogens in recurrent or treatment-resistant granulomatous mastitis. A comprehensive microbiological workup, including mycobacterial culture, is essential before initiating immunosuppressive therapy. The identification of MAC as the causative organism fundamentally altered the management strategy.

Conservative management during pregnancy, followed by targeted postpartum antimycobacterial therapy, can achieve complete resolution in MAC-associated granulomatous mastitis, even in immunocompetent patients.