Effluvium, anagen

Abstract

Anagen effluvium is a form of nonscarring alopecia commonly associated with chemotherapy. In this disorder, affected anagen hairs suffer a toxic or inflammatory insult, resulting in fracture of the hair shaft.[1][2][3] Anagen effluvium is often referred to as chemotherapy-induced alopecia, as it can be triggered by antimetabolites, alkylating agents, and mitotic inhibitors administered as chemotherapeutic therapy. Shedding usually takes place within 14 days of administration of the offending drug, however, in many instances it is reversible, with hair regrowth growth upon discontinuation of the offending agent. The hair shaft is commonly damaged, and tapered fractures of anagen hairs can be appreciated on trichoscopy. An understanding of the cyclical phases of hair growth and anatomy of the hair follicle is essential to understanding anagen effluvium. There are roughly 100,000 hairs on the scalp; any given hair is constantly cycling between three stages: anagen, catagen, and telogen. Anagen is a growth phase, lasting between 2 and 6 years with an average of 3 years. Approximately 90% of hairs taken from a normal scalp are anagen hairs. This is a period of epithelial proliferation, in which bulb matrix cells undergo mitosis and proliferation to form the hair shaft. Severe insult to the hair bulb or hair matrix in the form of medications, toxin exposure, or inflammation that causes a cessation of this mitotic activity can cause damage to the hair shaft resulting in breakage, and if the bulb is affected, complete hair loss. Catagen is a transitional phase between anagen and telogen, and in this phase, all growth ceases. Less than 1% of scalp hairs are in catagen at any given time. Telogen is a resting phase, lasting approximately 3 to 5 months, immediately before the hair falls out (teloptosis). Telogen effluvium, a separate entity, occurs when anagen hairs are prematurely shifted into the telogen phase triggered by medications, physical or psychological stressors, hospitalization, pregnancy, among other causes. Kenogen is the lag phase between loss of telogen hair and the growth of a new hair.[4][5][6]