Ultrastructural aspects of equine pemphigus foliaceus-like dermatitis. Report of cases.

Pemphigus foliaceus is an uncommon dermatologic disorder occurring in several species and has been reported in horses during the past decade. An ultrastructural analysis of affected skin of horses presenting to our clinics has revealed early cytopathologic features of pemphigus-like disease, some of which closely resemble pemphigus foliaceus in the human, calve, and guinea pig. Prior to complete acantholysis and bullae formation, the intercellular spaces enlarged, but intercellular bridges and desmosomes remained intact. A novel finding was presence of aggregates of electron dense granular material which were seen in intercellular spaces of the epidermal basal cell layer, and may represent antigen-autoantibody complexed material or deranged cement substances. Other changes preceding acantholysis consisted of mild dyskeratosis, reduction of peripheral tonofilaments, enlargement of rough endoplasmic reticula, cytoplasmic vacuolization, and mitochondrial damage in epidermal cells. In more severe lesions where bullae were present and acantholysis was observed, bacterial invasion and leucocytic infiltration were evident in all epidermal layers, and corneal cells displayed cytoplasmic vacuolization and retention of nuclei. Basal cells remained intact, though intercellular spaces were enlarged on apical and lateral boundaries. The pathogenesis of this disease in the horse appeared morphologically similar to a pemphigus autoimmune disorder and its variants in other species, and morphologic evidence is provided to suggest that some cellular metabolic derangements may be concurrent with the extracellular events or cell peripheral changes that precede acantholysis and bullae formation.