Granulomatous mastitis--a rare cause of erythema nodosum.

Granulomatous mastitis is a recently described, rare condition of unknown aetiology. It occurs in young, parous women as a tender extra-areolar breast lump and therefore needs to be differentiated from carcinoma. Histologically, a discrete granulomatous lobulitis is seen and because of morphological similarities to granulomatous thyroiditis it has been suggested it may be immunologically mediated. We present a patient in whom granulomatous mastitis presented with periarthritis and erythema nodosum, an association not previously described.