Morphologic and Immunologic Characterization of a Canine Isthmus Mural Folliculitis Resembling Pseudopelade of Humans

The study characterized a novel form of isthmus mural folliculitis in dogs, resembling human pseudopelade, by examining clinical, histopathologic, and immunopathologic features. Affected dogs showed persistent alopecia that did not respond to treatment. Histopathology revealed lymphocyte infiltration in the follicular isthmus, with inflammation sometimes extending but not involving the hair bulb or epidermis. Severe follicular and sebaceous gland atrophy was observed. The presence of CD3 and CD8 lymphocytes and autoantibodies targeting lower hair follicle proteins, including hair keratins, was noted. The findings, including lack of hair regrowth and extreme adnexal unit atrophy, were similar to human pseudopelade.