Erythema multiforme in two horses.

This research reports the first occurrence of Erythema multiforme, a type of skin disease, in two South African horses that each displayed raised, non-hair-losing, non-itchy skin patches symmetrically over the neck and trunk areas. The cause of the disease could not be identified, but both horses naturally recovered within three months.

Introduction

• The researchers reported the first known occurrences of a skin disease known as Erythema multiforme in two South African horses. This disease is marked by the sudden outbreak of specific skin lesions.

Presenting Symptoms

• Both horses displayed raised skin patches (plaques) that were non-pruritic (not itchy) and non-alopecic (not causing hair loss), found over the dorsolateral aspects (upward and sideways areas) of the neck and trunk.
• In both cases, these skin patches were distributed in a bilaterally symmetrical manner, mirrored on each side of the body.

Histopathological Findings

• The researchers conducted histological analyses on the horses, which involved studying the microscopic structure of tissue in order to understand the disease manifestation.
• The findings included hydropic degeneration of basal epidermal cells, meaning the lower layer of skin cells showed symptoms of disease-deterioration due to water buildup.
• There was eosinophilic necrosis of individual or groups of keratinocytes, indicating the death of certain skin cells typically associated with an immune response, possibly related to inflammation or allergic reactions.
• Evidence of intra-epidermal and sub-epidermal cleft formation was found, suggesting the creation of gaps or spaces within and beneath the skin layers.
• Additionally, mixed dermal perivascular infiltrates were present, indicating that there was a mixture of cell types penetrating into the area surrounding the blood vessels in the skin (dermis).

Cause and Remission

• Even with this comprehensive examination of the disease symptoms, the researchers could not identify the initiating cause in either case.
• The silver lining in this research is that both horses underwent a gradual spontaneous remission, meaning they naturally recovered from the disease without specific treatment within a period of three months.