Comparison of hair follicle histology between horses with pituitary pars intermedia dysfunction and excessive hair growth and normal aged horses.

Marie Innerå, Annette D Petersen, Danielle R Desjardins, Barbara A Steficek, Edmund J Rosser, Harold C Schott

Department of Small Animal Clinical Sciences, Diagnostic Center for Population and Animal Health, College of Veterinary Medicine, Michigan State University, East Lansing, MI 48824, USA.

Veterinary dermatology 2013 Feb

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Pituitary pars intermedia dysfunction (PPID) in older equids is commonly recognized by a long hair coat that fails to shed. The aim of this study was to compare hair follicle stages in PPID-affected horses with excessively long hair coats with the stages of normal aged horses (controls) and to compare hair follicle stages in PPID-affected horses after 6 months of treatment with pergolide mesylate with those of control horses. Eight PPID-affected horses and four normal, age-matched, control horses. Skin biopsies were collected from the neck and rump of PPID-affected and control horses. A diagnosis of PPID was established based on hair coat changes and supportive overnight dexamethasone suppression test results. Skin biopsies were repeated after 6 months of treatment with pergolide. The number of hair follicles in anagen (A) or telogen (T) was counted for each skin biopsy using transverse sections. Pretreatment biopsies had a greater percentage of A follicles (neck 96%, rump 95%) and a lower percentage of T follicles (neck 4%, rump 5%) in PPID-affected horses than in control horses (A, neck 15%, rump 25%; and T, neck 85%, rump 75%). After treatment with pergolide, all PPID-affected horses had improved shedding, and the percentages of A follicles (neck 69%, rump 70%) and T follicles (neck 31%, rump 30%) were not different from untreated control horses (A, neck 68%, rump 82%; and T, neck 32%, rump 18%). These findings document that excessive hair growth (hypertrichosis) in PPID-affected horses is due to persistence of hair follicles in A. Furthermore, treatment with pergolide improved shedding and reduced the percentage of A follicles in PPID-affected horses. © 2013 The Authors. Veterinary Dermatology © 2013 ESVD and ACVD.

Citation

Marie Innerå, Annette D Petersen, Danielle R Desjardins, Barbara A Steficek, Edmund J Rosser, Harold C Schott. Comparison of hair follicle histology between horses with pituitary pars intermedia dysfunction and excessive hair growth and normal aged horses. Veterinary dermatology. 2013 Feb;24(1):212-7.e46-7