CANINE DEMODICOSIS - A REEXAMINATION OF THE HISTOPATHOLOGIC LESIONS AND DESCRIPTION OF THE IMMUNOPHENOTYPE OF INFILTRATING CELLS

This study describes the inflammatory patterns and immunophenotype of the histologic lesions of canine demodicosis. Three major patterns were identified: mural folliculitis, suppurative folliculitis and furunculosis and nodular dermatitis. Mural folliculitis, an inflammatory reaction targeting the follicular wall, was seen in all cases and was the principle pattern in 17 of 34 cases (50 per cent). The interface subtype of mural folliculitis, typified by hydropic degeneration or apoptosis of follicular keratinocytes and lymphocytic exocytosis, occurred in 15 of these 17 cases. Follicular melanosis and/or pigmentary incontinence occurred in 10 of these 17 biopsies. Nodular dermatitis, represented by perifollicular granulomas, was present in nine biopsies (26 per cent). Suppurative folliculitis or furunculosis was the dominant pattern in eight cases (24 per cent). All lymphocytes within the follicular wall were CD3+ T lymphocytes, compared to 10 per cent of the perifollicular cells. IgG(+) plasma cells accounted for up to 74 per cent of perifollicular cells, highest in cases with furunculosis. These findings indicate that mural folliculitis is an important lesion of canine demodicosis, and suggests that a cell-mediated reaction is targeting the follicular wall.