Idiopathic granulomatous mastitis (IGM) is a rare, chronic, granulomatous, inflammatory disorder with potentially misleading clinical and radiological features. IGM is diagnosed after exclusion of infectious or tumoral diseases. Herein we report a case of erythema nodosum associated with IGM, which serves as a reminder that erythema nodosum may constitute an extra-mammary sign of IGM.A 36-year-old nulliparous woman presented with fever and skin rash at our dermatology clinic at the North Franche-Comté hospital in July 2017. Symptoms had occurred 2 days previously. The patient had a fever of 38.8°C and typical erythema nodosum on the limbs. Physical examination showed an irregular, inflammatory, abscessed mass measuring 20cm with multiple shrinkage zones that had been developing for 4 weeks and for which breast examinations were being performed. Laboratory tests showed an inflammatory state (CRP 155mg/mL, WBC 14.6×109/L), other tests (serum electrolytes and calcium, hepatic and renal tests, Streptotest, T-spot, HIV, HBV, HCV serology, anti-streptolysin, anti-streptodornase, local microbiology samples, antinuclear antibodies, soluble antigens antibodies, hemocultures, angiotensin-converting-enzyme and chest x-rays) were normal. Microbiology investigations were negative. Mammography revealed invasive mastitis. Breast sample biopsies showed giant cell granulomas without caseous necrosis or tumor cells, and histochemical staining (PAS, Ziehl, Grocott, Gram) was negative. The final diagnosis was of IGM associated with erythema nodosum. Symptoms rapidly improved with oral steroids.As reported herein, erythema nodosum may be associated with IGM and support the diagnosis thereof. This association is rare, with fewer than 30 case reports described in the literature. IGM is an uncommon benign disorder of the breast that can mimic two frequent breast disorders: breast carcinoma and breast abscess. It usually occurs in young sexually active women. It appears as a tumor with an inflammatory solid painful mass, with nipple and skin retraction, occasionally with abscesses and accompanied by homolateral axillary lymphadenopathies. Radiologic findings are usually not specific for or suggestive of cancer. The histopathological picture of IGM is characterized by the presence of multinucleated giant cells and epithelioid histiocytes forming non-caseating granulomas around lobules. Minor ductal and periductal inflammation is usually present. IGM is rarely associated with autoimmune system manifestations, especially erythema nodosum, arthritis, episcleritis or hidradenitis suppurativa. Although the physiopathology of IGM remains unclear, this case serves as additional evidence that the etiology of IGM is of autoimmune origin. While there is no recommendation for the treatment of IGM, oral steroids remain the cornerstone of therapy.We report a case of IGM associated with erythema nodosum. Dermatologists must be aware of this association.
