Feline Pemphigus Foliaceus

Pemphigus foliaceus (PF) is the most common autoimmune dermatosis in cats and occurs when circulating autoantibodies (most commonly immunoglobulin G) bind to structural components within the superficial epidermal desmosomes and induce cell separation (ie, acantholysis). Breed and sex predispositions have not been reported in cats; median age of onset is 5 years of age.¹

Pustules, the primary lesions of PF, are rarely observed in cats due to their superficial location within the epidermis. Thin-roofed pustules rapidly rupture to form crusts with underlying erosions. Coalescing regions of exfoliation and adherent crusts can become painful and exudative in cases with secondary bacterial infection or affected footpads.

Although lesions most frequently develop at or around the nasal planum, muzzle, pinnae (Figure 1), perimammary skin, mammary nipples (Figure 2), ungual folds, and footpad margins (Figure 3), full body involvement is also possible.^2-4 Exudates within the ungual folds can be exuberant, and PF is a primary differential for paronychia affecting multiple digits in cats (Figure 4).

FIGURE 1 Classic pattern of feline PF, with adherent crusts around the face, dorsal muzzle, periorbital region, and pinnae

FIGURE 2

Thick, erythematous crusts surrounding the mammary skin

FIGURE 3

Excessive scaling of the footpads with crusts adherent to the footpad margins and claws

FIGURE 4

Thick, purulent exudate from the ungual fold

Diagnosis

Tentative diagnosis is possible with examination of pustule contents. Pustule cytology should reveal individual to rafts of immature, free-floating (acantholytic) keratinocytes, as well as intact neutrophils and occasional eosinophils (Figure 5). Definitive diagnosis requires histopathologic examination of skin biopsy tissue. Samples that include an intact pustule (if present) are preferable, and crusts should be included, as acantholytic keratinocytes are often identified within the crusts.

FIGURE 5

Cytologic preparation showing neutrophils and large, rounded (acantholytic) keratinocytes

Treatment

Treatment requires immunosuppressive therapy. Single modality and multidrug treatment plans have been described⁵; treatment with corticosteroids alone is often successful in cats.

Prednisolone (2-6 mg/kg PO every 24 hours) or dexamethasone (0.22 mg/kg PO every 24 hours) may be prescribed as the initial corticosteroid choice. Because of poor bioavailability of prednisone in cats, prednisolone is preferred over prednisone. Dose and frequency of administration should be tapered based on response. More selective immunosuppressive drugs (eg, modified cyclosporine, 7 mg/kg PO every 24 hours; chlorambucil, 2 mg/m² PO every 48 hours) can be added to permit reduced corticosteroid administration if response to initial treatment is insufficient. Oclacitinib has also demonstrated efficacy at controlling clinical signs.^6,7 Monitoring with frequent rechecks and routine CBC and serum chemistry profile measurement (based on formulary recommendations for specific drugs) are needed for medication adjustments.

In general, secondary bacterial infections are a less significant concern in cats than in dogs; however, the presence of bacteria in cytologic preparations requires infection control with systemic antibiotics and topical antiseptic therapy. Cases complicated by previous antibiotic administration may require exudate culture and susceptibility testing for selection of appropriate medication.

Prognosis

Prognosis is fair to good with effective therapy. Affected cats benefit most from aggressive initial treatment that induces remission, followed by maintenance therapy for long-term disease control. Lifelong therapy with immunosuppressive drugs is needed in almost all patients, as permanent remission is uncommon to rare.^2,3