Spongiotic vesicular dermatitis as a cutaneous reaction pattern in seven horses

Over a 6-year period seven adult horses of different breeds and genders dev eloped multifocal, exudative, oozing dermatitis characterized histologicall y by epidermal spongiotic vesicles and perivascular eosinophilic, neutrophi lic and mixed mononuclear inflammation. Three horses were pruritic. Systemi c disease was not noted. Two horses had a history of recurrent urticaria (h ives) and one horse had nodules or welt-type lesions that progressed to exu dative, oozing lesions. Interepithelial immunoglobulin (Ig)G was detected b y avidin-biotin complex-peroxidase staining, but the pattern of staining wa s more consistent with epithelial oedema than specific IgG deposition assoc iated with pemphigus. The exudative oozing lesions developed under circumst ances suggesting that dermal oedema progressed to intracellular and interce llular epidermal oedema, which in turn progressed to the spongiotic vesicul ar epidermal lesions.