title: Histopathologic features of canine distichiasis.
abstract: OBJECTIVE
  To describe the histologic features of canine distichiasis using excised tarsoconjunctival specimens that included roots of distichiatic cilia.
  
  
  METHODS
  The study group included 21 strips of cilia-bearing tarsoconjunctiva resected from 20 dogs with distichiasis. Eyelid tissue specimens were also collected from 11 euthanized dogs without distichiasis to serve as controls. All flat mount preparations were processed for histologic examination, and serial sections were stained with hematoxylin-eosin (H&E). A total of 157 slides were examined for the study group to describe the follicles and path of the distichiatic hairs and determine their potential connection with the tarsal glands. A total of 82 slides were examined for the control group.
  
  
  RESULTS
  In 19 of the 20 dogs with distichiasis, serial sections of the specimens identified anatomic segments of hair follicles located abnormally in the eyelid tarsus and associated with the aberrant cilia. They appeared as hair bulbs adjacent to tarsal glands, middle portions of hair follicles located between sebaceous lobules, and single or multiple hair shafts present within the sebaceous duct. The tarsal glands in the cilia-bearing tarsoconjunctiva were not different from those of the controls, in which no distichiatic hair bulbs or shafts were observed.
  
  
  CONCLUSIONS
  These results demonstrate that adventitious cilia are not associated with histologic changes of the tarsal glands, and appear to arise from ectopic hair follicles present in the tarsus. Canine distichiasis may result from anomalous regulation of morphogenesis of hair follicles in the mesenchymal tissue of the tarsal plate.
authors: Department of Clinical Sciences, National Veterinary School, 23 chemin des Capelles BP 87614, 31076 Toulouse Cedex 3, France.
authors: Isabelle
authors: I
authors: Raymond-Letron
authors: Nathalie
authors: N
authors: Bourges-Abella
authors: Tiphaine
authors: T
authors: Rousseau
authors: Jean-Yves
authors: JY
authors: Douet
authors: Georges
authors: G
authors: de Geyer
authors: Alain
authors: A
authors: Regnier
mesh_terms: D000818:Animals; D016022:Case-Control Studies; D004283:Dog Diseases / Q000473:pathology*; D004285:Dogs; D005140:Eyelashes / Q000002:abnormalities*; D005141:Eyelid Diseases / Q000473:pathology / Q000662:veterinary*; D005260:Female; D018859:Hair Follicle / Q000002:abnormalities; D008297:Male