Chronic granulomatous mastitis (CGM), also commonly referred to as idiopathic granulomatous mastitis or granulomatous lobular mastitis, is a rare benign inflammatory condition of the breast. It usually affects women in their childbearing years, and the majority of affected patients have a history of ceasing lactation within the preceding 6-24 months. The etiology of the condition is poorly understood. Hyperprolactinemia and smoking are established risk factors. Corynebacterium species have been consistently isolated in CGM, but a causal effect has not yet been established.

Patients with CGM present with a palpable breast lump, indurated plaque, or fluctuant nodule that is typically painful. With progressing disease, fistulas may occur, leading to purulent drainage. CGM is typically unilateral but may be bilateral in up to 25% of cases. Erythema nodosum (EN) has been reported to occur in patients with CGM, with onset after the diagnosis of CGM, suggesting that CGM may be the trigger for EN, although some authors speculate that the 2 conditions may share the same pathogenetic mechanisms. Other reported extramammary inflammatory manifestations include arthralgias and episcleritis.

CGM is a diagnosis of exclusion. It is crucial to rule out breast carcinoma with mammography, ultrasound, and core needle biopsy. Core needle biopsy should also be sent for culture to rule out infectious etiologies. In addition, other causes of granulomatous disease, such as sarcoidosis or rheumatologic disease, may be considered.

To date, there is no established treatment algorithm. From case series and case reports, antibiotics, corticosteroids, and/or immunosuppressants may be helpful for some patients. The natural course of the disease is not well-described: some patients spontaneously regress, others improve with therapy, and some relapse or have resistant disease despite treatment.

See also mastitis.