"Sine Phenomenon" in Dermatology

Background: In dermatology, the term sine is often used in regard to any sign, symptom or finding whose absence would very likely mean uncommon variant of the target disease or condition. Sine phenomenon can be seen in different dermatological diseases such as scleroderma, polymorphic light eruption, dermatomyositis, pellagra, zona, psoriasis, necrobiosis lipoidica, lupus erythematosus, seborrheic keratosis, eccrine hidradenitis and acne fulminans.