Cogan syndrome: A rare form of artery inflammation (arteritis) of unknown cause that affects the ear. Cogan syndrome causes problems of hearing and balance and also inflammation of the cornea and often fever, fatigue, and weight loss. Joint and muscle pains can also be present. Less frequently, the arteritis can involve blood vessels elsewhere in the body, as in the skin, kidneys, nerves, and other tissues and organs. Cogan syndrome can lead to deafness or blindness. Treatment is directed toward stopping the inflammation of the blood vessels. Cortisone-related medications, such as prednisone, are often used. Severe disease can require immunosuppression medications, such as cyclophosphamide.