Dermatological and morphological findings in quarter horses with hereditary equine regional dermal asthenia.

This study is about Hereditary Equine Regional Dermal Asthenia (HERDA), a skin disorder in quarter horses, and is aimed at understanding the changes in skin thickness and structure in affected horses. The study concludes that there is significant variation in skin thickness in affected horses and that molecular testing is a critical determinant for a definitive diagnosis.

Objectives and Methodology

The research chiefly had two objectives:

• To examine and characterize the variation in skin thickness and structural abnormalities in quarter horses that are affected by HERDA.
• To ascertain the strength of agreement between independent observations and the diagnostic accuracy of histopathological examination of skin biopsies for HERDA diagnosis.

The researchers used a total of six HERDA-affected quarter horses which were DNA confirmed, from a research herd, and five unaffected quarter horses from a stud farm. They measured skin thickness in 25 separate body regions on both sides in all of the affected and unaffected horses, after which they carried out a histopathological and ultrastructural evaluation of the skin biopsies.

Findings and Results

The research found that in all evaluated regions, the average skin thickness of the affected horses was thinner compared to unaffected ones. However, a statistically significant difference was only observed when the average magnitude of the difference was greater than or equal to 38.7%.

• The agreement between different observers for the histopathological examination ranged from fair to substantial.
• The histopathological sensitivity for HERDA diagnosis varied between observers and ranged from 73% to 88%.
• The specificity of the histopathological examination varied depending on the region sampled and ranged from 35% to 75%.

Conclusions

Despite the regional distribution of cutaneous signs, skin with decreased thickness was not regionally distributed in the HERDA-affected horses. The findings imply that histopathological examination is informative but not definitive for establishing a HERDA diagnosis. Skin samples from the neck, croup, or back proved useful in HERDA diagnosis. However, a definitive diagnosis required confirmation using molecular testing.