Anti-isthmus autoimmunity in a novel feline acquired alopecia resembling pseudopelade of humans

Pseudopelade is a primary scarring (cicatricial) alopecia of humans charact erized by lymphocyte-rich inflammation centred around the hair follicle ist hmus. Lymphocyte folliculotropism is associated with isthmus apoptosis and, ultimately, follicular destruction and dermal fibrosis. In a cat, an acqui red alopecia was diagnosed as pseudopelade based on the following criteria: (i) an adult-onset, patchy to diffuse nonpruritic hair loss; (ii) an early folliculo-destructive phase in which lymphocytes and dendritic cells accum ulated in and around the follicular isthmus; and (iii) a late stage in whic h the lower segments of hair follicles underwent atrophy and were replaced by fibrosing tracts. Additionally, immunological investigations characteriz ed the cytotoxic phenotype of isthmotropic lymphocytes and demonstrated the presence of circulating IgG autoantibodies specific for multiple follicula r antigens. Altogether, the results of the present study suggest an immune- mediated pathogenesis for this case of feline pseudopelade, similarly to th at causing alopecia areata in humans and other mammalian species.