Autoimmune dermatologic diseases are relatively rare in cats. Pemphigus foliaceus (PF) is the most common of these, wherein autoantibodies are responsible for destroying the proteins that bind epidermal cells together. The pathomechanism associated with the lesions of PF has not been elucidated in the cat as definitively as it has in the dog, but is assumed to be similar. Autoantibodies (usually IgG) produced by the animal bind to desmoglein 1, an intracellular adhesion molecule that, in association with plakoglobin, a desmosomal plaque protein, normally binds keratinocytes together in the superficial epidermis. The trigger for development of autoantibodies in the affected animal is often unknown; it may include drugs, toxins, allergies, or even emotional stress, as has been reported in humans with PF. There is no reported association of feline leukemia or feline immunodeficiency virus infection in cats with PF, and no association with vaccination in either cats or dogs.

Grossly, the primary lesions of PF are pustules covered fully or partially by crusts. The pustules initiate in subcorneal spaces within the epidermis that are opened up by the breakdown of normal adhesion between keratinocytes, and then these spaces fill with neutrophils, which are attracted to the sites by inflammatory mediators. The lesions of PF are variably pruritic and/or painful, and there may be secondary bacterial infection due to disruption of the epidermal barrier.  The clinical course of this disease typically waxes and wanes.  Areas of the body most commonly and initially affected include the head (eyes, periocular areas, ear pinnae, nose, chin, lips, and/or planum nasale) and feet (nail beds and paw pads). The disease may eventually spread to other parts of the body. As an autoimmune disease, PF may be successfully managed but not cured, and the best possible outcome is remission, as it is always possible that the disease may recrudesce in the future. Many cats with PF require lifelong immunosuppressive therapy.

Various treatments have been advanced for feline patients with PF. In general, glucocorticoids are considered the treatment of choice for this disease due to their immunosuppressive properties, and the most commonly selected glucocorticoid treatment for feline PF is prednisolone. Prednisolone is preferred over prednisone in cats, as oral prednisolone has more favorable pharmacokinetics in cats than prednisone.

If there is poor response to prednisolone, triamcinolone or dexamethasone may be employed, but these agents are significantly more potent than prednisolone and should be used with care. Chlorambucil is also sometimes used as a single agent in lieu of glucocorticoids, or along with them in a glucocorticoid-sparing protocol. Other less commonly used agents include cyclosporine (may be used in conjunction with glucocorticoids), cyclophosphamide (which probably offers no advantages over chlorambucil), and gold salts (chrysotherapy); all of these are associated with significant side effects.

This article reports the results of a retrospective study of the records of 37 client-owned cats, patients at a veterinary dermatology referral practice between the years of 1995 and 2013. All of the cats were treated with prednisolone monotherapy for PF. Histopathology was used to confirm the diagnosis of PF in 23/37 of the patients, while in 14/37, a combination of cytological findings, history, clinical signs, and response to treatment was used to make the diagnosis. Previous studies had reported that remission of feline PF could be induced with prednisolone doses of 4-6.6 mg/kg/day, and it was the aim of the authors to determine if lower doses of prednisolone as monotherapy could have the same result.

Complete remission of the PF signs within 8 weeks of starting treatment with a median induction dose of  2 mg/kg of prednisolone daily was achieved in 36/37 (97%) of the patients.  Most of the patients (33/37; 89%) actually achieved remission on this regimen in 4 weeks or less. Thirty of the 37 patients required maintenance prednisolone therapy to remain in remission, while 7 were free of medication at the conclusion of the study.  Sixty-seven percent of the cats who continued to require medication were controlled with prednisolone monotherapy. The median maintenance dose of prednisolone was 1.2 mg/kg/week.

The authors speculate that in those animals demonstrating resistance to treatment, emotional stress may play a role as it does in humans, but this association has not been investigated in animals. Anxiolytic medications are sometimes used in the adjunctive treatment of people with PF.

After achieving complete remission, 25 of the 37 cats with PF relapsed with disease, usually within 6 months or less from the time of initial diagnosis, while medication was being tapered. However, the protocol used in tapering individual patients was not standardized in the study, given its retrospective nature.

Reported adverse effects of prednisolone monotherapy were uncommon. The authors conclude that prednisolone at 2 mg/kg/day is effective in inducing remission in almost all cats with PF, and in a small number, this remission may be permanent. They also found that in cats with PF-associated claw fold disease (81% of patients included in the study), the frequently found bacterial overgrowth in the claw fold exudate responded to immunosuppressive therapy only without antimicrobial therapy. The latter is often recommended for cats with PF due to the presence of intracellular bacteria within neutrophils contained in the exudate. This indicates that the bacteria found in PF claw-fold pustules are not present in association with a primary infection, but are colonizing opportunistically, and they may disappear easily without antibiotic treatment once the patient is started on prednisolone.

The authors point out that not all patients included in the study had a histopathologic diagnosis of PF.  Although histopathologic diagnosis is most desirable, client economic constraints or limitation of the disease to claw folds as the only affected site may prohibit biopsy and histopathology. If the only option to obtain a biopsy specimen is amputation of the cat’s third phalanx, they state that this permanently disfiguring and painful procedure may provide little additional data over cytology alone. [PJS]