Zonal dermal separation: a distinctive histopathological lesion associated with hyperelastosis cutis in a Quarter Horse.

This research paper presents a unique case where a one-year-old Quarter Horse with hyperelastosis cutis exhibited a specific skin lesion that the researchers termed ‘zonal dermal separation’. This condition was identified via the examination of skin biopsies and subsequent necropsy, with advice to future researchers to be careful in their biopsy selection to adequately capture the full extent of the disorder.

Introduction and Observations

• The paper starts by detailing an unusual skin lesion found in a one-year-old Quarter Horse filly which was exhibiting symptoms of hyperelastosis cutis
• Hyperelastosis cutis is characterized by excessively stretchy and fragile skin
• The symptoms had a history of around six months, after the filly experienced minor skin trauma which consequently developed into cutaneous wounds.

Methodology and Findings

• The researchers collected punch biopsies of skin from both the affected horse and a similar, unaffected control horse.
• On comparison, they found that the skin biopsies from the affected horse were noticeably thinner than those from the healthy horse.
• However, initial staining procedures (haematoxylin and eosin and Masson’s trichrome stains) applied on the biopsies did not show any significant microscopic lesions.
• When the researchers examined the ultrastructure of the dermis from the affected horse, they found variations in collagen fibre diameter and loosely packed collagen fibres within the bundles – a variation from the norm.

Necropsy and Conclusion

• The horse was eventually euthanized for a full necropsy, during which full-thickness sections of the skin were collected for a more comprehensive study.
• While the skin was of normal thickness, the researchers noted a distinct horizontal zone in the deep dermis where the collagen bundles exhibited separation, leading to large, empty cleft-like spaces.
• They suggest naming this microscopic lesion “zonal dermal separation”.
• In the light of these findings, the research team concluded by recommending incisional full-thickness skin biopsies for suspected cases of equine hyperelastosis cutis, as they believe punch biopsies may not accurately capture the pathological changes in the horse’s skin.