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 wer e identified: mural folliculitis, suppurative folliculitis and furuncu losis and nodular dermatitis. Mural folliculitis, an inflammatory reac tion targeting the follicular wall, was seen in all cases and was the principle pattern in 17 of 34 cases (50 per cent). The interface subty pe of mural folliculitis, typified by hydropic degeneration or apoptos is of follicular keratinocytes and lymphocytic exocytosis, occurred in 15 of these 17 cases. Follicular melanosis and/or pigmentary incontin ence occurred in 10 of these 17 biopsies. Nodular dermatitis, represen ted by perifollicular granulomas, was present in nine biopsies (26 per cent). Suppurative folliculitis or furunculosis was the dominant patt ern in eight cases (24 per cent). All lymphocytes within the follicula r wall were CD3+ T lymphocytes, compared to 10 per cent of the perifol licular cells. IgG(+) plasma cells accounted for up to 74 per cent of perifollicular cells, highest in cases with furunculosis. These findin gs indicate that mural folliculitis is an important lesion of canine d emodicosis, and suggests that a cell-mediated reaction is targeting th e follicular wall.