Degenerative mucinotic mural folliculitis in cats

A novel form of mural folliculitis is described in seven cats. Clinically, all cats exhibited generalized alopecia with scaling or crusting that was more pronounced over the head, neck, and shoulders. The face and muzzle of all cats was unusually thickened. Six of seven cats were progressively lethargic but did not demonstrate any other consistent systemic abnormalities. Histologically, there was severe mixed inflammation of the wall of the follicular isthmus in all cats, accompanied by some follicular destruction in five cats. Sebaceous glands were not affected. All cats had variable, but often striking, follicular mucin deposition, as well as epidermal hyperkeratosis and crusting. The cause of the severe mural folliculitis was not identified, and all cats responded poorly to immunomodulating therapy. Follicular mucinosis may be a nonspecific finding, likely reflective of the follicular lymphocytic milieu, and does not always herald follicular lymphoma.