A retrospective review of hyperaesthetic leucotrichia in horses in the USA.

The research conducted a retrospective review on a rare condition in horses identified as hyperaesthetic leucotrichia (HL), comparing it with erythema multiforme (EM), to describe the clinical and histological features, their similarities and differences. The study discovered that HL primarily affects Arabian and American paint horses, usually occurring in summer and has the potential to recur.

Study Methodology

• The researchers conducted a retrospective review of medical records from 1985 to 2015.
• Within these records, they identified 15 horses that had HL.
• They evaluated and compared thirteen biopsies of HL and five of EM.

Results and Findings

• Arabian horses and their crosses, as well as American paint horses, were found to be significantly overrepresented, suggesting that these breeds might be more susceptible to HL.
• In terms of timing, the onset of clinical signs was primarily between April and September.
• Common clinical signs included pain, leucotrichia (whitening of the hair), crusting, and alopecia (baldness), restricted to darkly pigmented skin.
• From the sample, lesions recurred seasonally in 6 of 12 horses and unpredictably in 1 of 12 as evidence of the recurring nature of this disease.
• Key histological features identified were largely stellate cells and oedema in the superficial dermis, perivascular to diffuse lymphocytic inflammation, pigmentary incontinence (loss of pigment), apoptotic keratinocytes (cell death in keratin-producing cells), and vesicle formation.
• Comparing these features with those from the horses with EM revealed significant differences: horses with EM had significantly more acanthosis (thickening of the skin), lymphocytic exocytosis (a process linked to inflammation), satellitosis (surrounding of inflamed cells by lymphocytes), and inflammation.
• In contrast, horses with HL had more pigmentary incontinence and superficial dermal oedema (swelling in the upper layer of skin).

Conclusion

• The study concluded that HL primarily affects Arabian horses and American paint horses.
• The condition generally manifests in summer and could return seasonally or unpredictably.
• Despite sharing some features with EM histologically, significant differences were discovered between these two diseases.