Canine Pemphigus Foliaceus

Pemphigus foliaceus, a common autoimmune skin disease in dogs, occurs when circulating autoantibodies (most commonly immunoglobulin G) bind to structural components within the superficial epidermal desmosomes and induce cell separation (acantholysis). Other less common pemphigus complex diseases include panepidermal pustular pemphigus, paraneoplastic pemphigus, pemphigus erythematosus, and pemphigus vulgaris.

Breed predispositions include Akitas, chow chows, dachshunds, English bulldogs, and spaniels; median age of onset is 4 years.¹ In most dogs, the underlying disease trigger is unknown; however, potential triggers have been identified, including vaccinations and various drugs (eg, antibiotics, NSAIDs, topical parasiticides).

Presentation

The primary lesions are large, superficial pustules that may be punctate or span multiple follicles; pustule contents may appear translucent to yellow (Figure 1). Pustules are thin-roofed and thus tend to rapidly rupture and form crusts with underlying erosions.

FIGURE 1 Flaccid pustule of pemphigus foliaceus spanning multiple follicles

This disease may naturally wax and wane, and lesions often develop in waves. In cases in which secondary bacterial infection develops or lesions affect the footpads, coalescing regions of exfoliation and adherent crusts can become tender and exudative. Pruritus may vary from minimal to severe.

Disease patterns include a facial pattern (ie, classic butterfly) that affects the nasal planum, dorsal muzzle, and periorbital and pinnal areas (Figure 2); thick adherent crusts at the footpad margins (Figure 3); and a truncal-predominant pattern (Figure 4).

FIGURE 2 Classic lesions of pemphigus foliaceus with thick crusts on the rostral muzzle, nasal planum, dorsal muzzle, and periorbital regions (ie, butterfly pattern)

FIGURE 3 Adherent crusts of pemphigus foliaceus on the footpad margins

FIGURE 4 Truncal-predominant lesions of pemphigus foliaceus consisting of multiple, coalescing crusted papules and patches

Diagnosis

Tentative diagnosis is possible with examination of the 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. Multiple lesion samples obtained via a ≥6-mm biopsy punch should be submitted to a pathologist with specialized training in dermatopathology. Samples that include an intact pustule (if present) are preferable, and crusts should be included, as acantholytic keratinocytes may be found in the crusts. Immunosuppressive therapy should be discontinued (if possible) prior to obtaining biopsy samples.

FIGURE 5 Cytology of a pemphigus foliaceus pustule; individual acantholytic (immature) keratinocytes (ie, fried eggs) are surrounded primarily by intact neutrophils

Treatment

Treatment requires immunosuppressive therapy using single or multiple drug regimens. Prednisone/prednisolone (1-4 mg/kg PO every 24 hours) is the most frequently prescribed corticosteroid for initial induction; dose and frequency of administration should be tapered based on response. More selective immunosuppressive drugs (eg, azathioprine, 50 mg/m² PO every 24 hours; modified cyclosporine, 5-7 mg/kg PO every 24 hours) are often included at treatment induction or added if there is insufficient response to initial treatment to permit reduced corticosteroid administration. Oclacitinib (0.5-1 mg/kg PO every 12-24 hours) has also demonstrated efficacy at controlling clinical signs.^2-7 Frequent rechecks and routine CBCs and serum chemistry profiles (based on formulary recommendations for specific drugs) are needed for medication adjustments. Drug choices and combinations may vary based on clinician preference and experience. For most patients, resolution of lesions with only occasional and transient pustules or crusts is considered adequate disease remission.

Secondary bacterial infection is a common complication of disease development. Treatment with systemic antibiotics is often initiated prior to histopathologic confirmation. In cases complicated by prior antibiotic administration, exudate culture and susceptibility testing may be required for medication selection. Frequent bathing with antiseptic shampoo (eg, chlorhexidine, ethyl lactate, benzoyl peroxide) to gently soak off crusts and exudates can significantly improve patient comfort, reduce length of antibiotic administration, prevent infection recurrence, and allow for better assessment of response to therapy.

Prognosis

Prognosis is fair to good based on response to treatment. Patients benefit from initial aggressive treatment to induce remission, followed by reduced therapy to maintain disease control. Lifelong therapy with immunosuppressive drugs is needed in almost all patients, as permanent remission is rare.