Mural folliculitis is a term that denotes a new syndrome recognised in cats. The common histological theme is lymphocytic and histiocytic infiltrate of the hair follicle in the outer sheath in the isthmus and infundibular regions. The infiltrate may extend to the epidermis, including neutrophils and eosinophils, and the follicles may be ablated by a pyogranuloma-tous inflammation leading to atrophy.
The main presenting clinical signs include generalised alopecia and scaling. There are five forms of this syndrome, which loosely groups different disease processes with a range of similar histological features.
One form of this condition is associated with epithe-liotropic lymphoma, another with sebaceous gland atrophy and sebaceous adenitis. The latter has been described in two forms. In one report a 10-year-old cat developed extensive hair loss and skin biopsies revealed an absence of sebaceous glands and pyogranuloma-tous inflammation around the hair follicles. In two other cases there was generalised heavy scaling of the body, partial alopecia and distinct rims of brown to black thick adherent scale along the margins of the eyelids; the author has seen a similar case. Histologically, there were similar changes in biopsies from both cats with no sebaceous glands. There is no effective treatment for sebaceous adenitis, although it may respond slightly to topical bathing. Glucocorticoids and retinoids may be worth considering if the condition proves to be similar to that reported in the dog.
Another form of mural folliculitis is associated with dermatophyte infection.
A fourth form is associated with pseudopelade-like disease. Pseudopelade is a rare condition reported in a cat, with clinical signs of alopecia, variable hyper-pigmentation and mild scaling. Histologically, evidence of cytotoxic T-lymphocytes targeting the follicle isthmus has been reported.
Other cases of mural folliculitis are associated with a variety of underlying causes. In some cases the cats seem to have a poor prognosis and may succumb to a neoplastic process, suggesting that mural folliculitis is a cutaneous reaction pattern, in some instances, for neoplasia - akin to paraneoplastic alopecia, hepato-cutaneous syndrome and thymoma disease. There may be an association with diet in some cases: in one report the lesions were histologically associated with an lymphocytic interface dermatitis and some apop-totic epidermal cells - the cutaneous lesions of thickened skin with adherent crusts over the head, dorsal neck and trunk. The footpads were dry and scaly. The cutaneous signs resolved with a change of diet.
The clinician should be mindful that this syndrome remains poorly understood and that a histological report including mural folliculitis should prompt a careful evaluation for a variety of possible underlying diseases.
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