PLEASE NOTE A NEW 4TH EDITION HAS BEEN PUBLISHED AND IS AVAILABLE IN THE LIBRARY AND IN PRINT

In veterinary dermatology, disorders of pigmentation are disorders of melanogenic pigmentation; the role of other factors that contribute to pigmentation in hairless skin, such as haemoglobin or carotenes, is anecdotal. Melanin pigments are synthesized in specialized cells, the melanocytes, which are present in the hair follicle and epidermal basal layer. Melanocytes are dendritic cells that send connections to a determined number of neighbouring keratinocytes, to form a pigmentary functional unit. In the epidermis every melanocyte is associated with 36 keratinocytes, whilst the bulbar melanocyte is associated with only four cortical keratinocytes. These follicular melanocytes have specific properties. They are taller than epidermal melanocytes and synthesize larger melanosomes, which are distributed individually to the cortical cells. They are characterized by cyclic activity, synthesizing melanin during the anagen phase and entering apoptosis during the catagen phase, to be replaced at the next cycle by non-differentiated cells that reside in the permanent upper part of the outer root sheath. This chapter considers the following: Hypopigmentation disorders; and Hyperpigmentation disorders.