Pohl-Pinkus constriction

a limited thinning of the shaft of a hair, usually accompanied by interruption of the medulla; it is usually a sign of systemic disease, but may be due to trauma, coronary occlusion, skin disease, or the therapeutic administration of a single substantial dose of an antimetabolite such as methotrexate or cyclophosphamide. Called also Pohl-Pinkus mark.