Bilateral granulomatous mastitis with a different etiology.

Idiopathic granulomatous mastitis (IGM) and Tuberculosis mastitis (TM) are rare inflammatory diseases of the breast that can clinically mimic malignancy causing misdiagnosis as breast cancer. We present a rare case of bilateral granulomatous mastitis with a different etiology. An initial lesion developed in the right breast was diagnosed as IGM, which was treated with antibiotics and surgery. A subsequent lesion developed in the contralateral breast 5 months later and was diagnosed as TM, which also completely responded to antituberculosis medication without surgical excision. Differential diagnosis was made using the results of the polymerase chain reaction for tuberculosis (TBC-PCR) of both of the breast lesions in addition to typical pathologic findings of IGM in the right breast and an antituberculosis medication response in the left breast. To the best of our knowledge, this is the first case of bilateral granulomatous mastitis with a different etiology.