title: A retrospective review of hyperaesthetic leucotrichia in horses in the USA.
abstract: BACKGROUND
  Hyperaesthetic leucotrichia (HL) rarely affects horses and causes painful lesions on the dorsum that result in leucotrichia. This may be a variant of erythema multiforme (EM), but there are no studies investigating this condition.
  
  
  OBJECTIVE
  Describe the clinical and histological features of HL and compare them to the histological features of EM.
  
  
  METHODS
  A retrospective review of medical records from 1985 to 2015 identified 15 horses with HL. Thirteen biopsies of HL and five of EM were evaluated and compared.
  
  
  RESULTS
  Arabian horses and their crosses (χ(2) (1)  = 8.56, P < 0.01) and American paint horses (χ(2) (1)  = 6.64, P < 0.05) were over represented. The onset of clinical signs was between April and September (14 of 15). The most common clinical signs were pain (15 of 15), leucotrichia (11 of 15), crusting (10 of 15) and alopecia (8 of 15) limited to darkly pigmented skin. The lesions recurred seasonally in 6 of 12 horses and unpredictably in 1 of 12 horse. The most common histological features were the presence of large stellate cells (13 of 13) and oedema (12 of 13) in the superficial dermis, perivascular to diffuse lymphocytic inflammation (13 of 13), pigmentary incontinence (12 of 13), apoptotic keratinocytes (9 of 13) and vesicle formation (8 of 13). Horses with EM (n = 5) had significantly more acanthosis (z = -2.40, P < 0.02) and lymphocytic exocytosis (z = -3.1, P < 0.004), satellitosis (Fisher's exact P = 0.02) and inflammation (z = -2.91, P < 0.004). Horses with HL had significantly more pigmentary incontinence (z = 2.13, P < 0.04) and superficial dermal oedema (z = 2.56, P < 0.002).
  
  
  CONCLUSIONS
  HL affects primarily Arabian horses and American paint horses. It occurs mainly in summer and may recur. Histologically HL shares features with EM, but there are significant differences between them.
authors.affiliation: William R. Pritchard Veterinary Medical Teaching Hospital, School of Veterinary Medicine, University of California Davis, 1 Garrod Drive, Davis, CA, 95616, USA.
authors.forename: Elizabeth C
authors.initials: EC
authors.lastname: Goodale
authors.affiliation: Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California Davis, 1 Garrod Drive, Davis, CA, 95616, USA.
authors.forename: Stephen D
authors.initials: SD
authors.lastname: White
authors.affiliation: Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California Davis, 1 Garrod Drive, Davis, CA, 95616, USA.
authors.forename: Catherine A
authors.initials: CA
authors.lastname: Outerbridge
authors.affiliation: William R. Pritchard Veterinary Medical Teaching Hospital, School of Veterinary Medicine, University of California Davis, 1 Garrod Drive, Davis, CA, 95616, USA.
authors.forename: Angela D
authors.initials: AD
authors.lastname: Everett
authors.affiliation: Department of Pathology, Microbiology & Immunology, School of Veterinary Medicine, University of California Davis, 1 Garrod Drive, Davis, CA, 95616, USA.
authors.forename: Verena K
authors.initials: VK
authors.lastname: Affolter
mesh_terms: D000818:Animals; D005260:Female; D020022:Genetic Predisposition to Disease; D006734:Horse Diseases / Q000453:epidemiology / Q000235:genetics / Q000473:pathology*; D006736:Horses; D008297:Male; D012189:Retrospective Studies; D012871:Skin Diseases / Q000453:epidemiology / Q000235:genetics / Q000473:pathology / Q000662:veterinary*; D014481:United States / Q000453:epidemiology