Tehran University of Medical Sciences Case Reports in Clinical Practice 2538-2683 4 3 2019 11 04 64 68 Sepehr Sahraiyan Department of Internal Medicine, Imam Khomeini Hospital Complex, Tehran University of Medical Sciences, Tehran, Iran. Mahsa Abbaszadeh Department of Internal Medicine, Imam Khomeini Hospital Complex, Tehran University of Medical Sciences, Tehran, Iran. Nasim KhajaviRad Department of Internal Medicine, Imam Khomeini Hospital Complex, Tehran University of Medical Sciences, Tehran, Iran. Sahar Karimpour Reyhan Department of Internal Medicine, Imam Khomeini Hospital Complex, Tehran University of Medical Sciences, Tehran, Iran. Ali Afshari Department of Internal Medicine, Imam Khomeini Hospital Complex, Tehran University of Medical Sciences, Tehran, Iran. 2019 07 23 2019 07 23 Granulomatous mastitis is a pathological diagnosis with a variety of causes, and its treatment depends on the underlying cause. We report a case of granulomatous mastitis in a 25-year-old woman admitted with erythema nodosum and an unresponded acute inflammatory mastitis to treatment. It was challenging for us to make a definite diagnosis between sarcoidosis and idiopathic lobular granulomatous mastitis for her. In the end, our diagnosis was sarcoidosis because of dactylitis we found in her physical examination which responded dramatically to nonsteroidal anti-inflammatory drug treatment. We started therapy with corticosteroids and immunosuppressant drugs and offered her continuous follow-up. https://crcp.tums.ac.ir/index.php/crcp/article/view/287 https://crcp.tums.ac.ir/index.php/crcp/article/download/287/318