chapter 22 Endocrinopathies, Atypical...............................
DEFINITION/OVERVIEW
Most common canine disorders affecting the hair coat and skin are hyperadrenocor-
ticism and hypothyroidism (discussed elsewhere).
Multiple disorders produce similar patterns of alopecia affecting the trunk but sparing
the head and distal extremities.
Hair coat and skin abnormalities may be recognized prior to the development of non-
dermatologic symptoms.
Uncommon disorders associated with abnormal hair follicle cycling and arrest include
sex hormone-related dermatoses and alopecia X.
Feline endocrinopathies such as diabetes mellitus and hyperthyroidism may have sec-
ondary effects on the skin and hair coat due to metabolic derangement or changes in
grooming behavior.ETIOLOGY/PATHOPHYSIOLOGY
The hair follicle cycle is influenced by both hormones and nonhormonal factors.
Endocrinopathies most often cause noninflammatory and symmetric alopecia.
Abnormalities may be the result of primary or secondary hyperfunction of, hypofunc-
tion of, or exogenous exposure to hormones.
Imbalances in sex hormones, especially elevations, can affect the hair cycle; sex hor-
mones and their precursors have intrinsic glucocorticoid actions and affinity for
glucocorticoid receptors, and may suppress the hypothalamic-pituitary-adrenal axis
(HPA).Abnormalities in the HPA axis may produce elevations in glucocorticoid precursor
hormones (notably androgens), with or without measured elevations in glucocorti-
coids.Alterations of hormones, in the absence of causality, may temporarily affect hair fol-
licle cycling; these changes often do not persist.
Blackwell’s Five-Minute Veterinary Consult Clinical Companion: Small Animal Dermatology, Third Edition.
Karen Helton Rhodes and Alexander H. Werner.
©2018 John Wiley & Sons, Inc. Published 2018 by John Wiley & Sons, Inc.
337