Nonpruritic hair loss

摘要

Monika Welle [Switzerland] opened the workshop by explaining that because many forms of alopecia in dogs are associated with hair cycle arrest, it is important to understand the hair cycle. Recently, two new stages have been characterized in dogs - exogen (shedding) and kenogen (hairless resting stage). The hair cycle consists of the phases anagen, catagen, tel-ogen and exogen (shedding) with a resting kenogen (hairless telogen) phase.In order to progress to anagen, stem cells from the bulge (an anatomical feature in mice but not in dogs or humans) grow down to form the inner root sheath and hair shaft. The precise stimulus is unknown. Later in anagen, the hair grows upwards. It thenregresses in catagen and the lower part undergoes apoptosis producing a telogen follicle. The telogen resting phase hair is firmly attached to hair follicle and it is not pushed out. Exogen, or shedding, is an enzymatic process between the hair and rootsheath and can occur at any time during the following cycle.