In most cats, pemphigus foliaceus is a mild and localized disease consisting of erosions and yellowish crusts. Pemphigus foliaceus
can also spread and become generalized in cats.15 Feline pemphigus foliaceus most commonly begins on the head (Figure 6). Lesions can also affect the pinnae. Cats can have marked suppuration and crusts on or around the footpads or ungual folds
of the claws (caseous paronychia; Figure 7).42,43 An onychodystrophy can also occur with these nailfold lesions.
6. Erosions and crusts on the face and ears of a cat with pemphigus foliaceus.
Infectious causes of pustular dermatitis can mimic or complicate pemphigus foliaceus.
7. Pedal pemphigus foliaceus in a cat.
Superficial pustular dermatophytosis is a fungal infection involving Trichophyton species. The lesions can look clinically and histopathologically similar to those of pemphigus foliaceus.44 While pustular dermatophytosis is uncommon,45 we recommend evaluating each case of suspected pemphigus foliaceus for dermatophytosis because of the negative consequences
of immunosuppressive treatment in patients with a dermatophyte infection.
A dermatophyte culture can diagnose superficial pustular dermatophytosis, and cytologic examination of the macroconidia from
the growth can identify the fungal species. The Trichophyton species that causes this form of dermatophytosis can be present both in the epidermis and in the hair follicle. Scale or
crust along with hair should be sampled for the dermatophyte culture. A periodic acid-Schiff (PAS) stain is required to differentiate
superficial pustular dermatophytosis from pemphigus foliaceus histologically.
Bacterial skin infections are another differential diagnosis for pemphigus foliaceus. Some staphylococci produce an exfoliative
toxin that targets desmosomes, resulting in clinical signs similar to those of pemphigus foliaceus.46 In these cases, large epidermal collarettes, often extending centrifugally, are present. Exfoliation tends to be more severe
in bacterial skin infections than in pemphigus foliaceus. Patients with bacterial skin infections will also demonstrate bacteria
cytologically. Cytologic examination often shows degenerative neutrophils with the bacteria. Culture of the exudate from within
a pustule can identify the bacterial species.
Pemphigus foliaceus is diagnosed by evaluating the clinical history, physical examination findings, and results of diagnostic
tests such as cytologic and histologic examinations (Table 1). Because of the potential for severe side effects, pemphigus foliaceus should be definitively diagnosed before systemic
immunosuppressive therapy is started.
Table 1: Diagnostic Criteria for Canine and Feline Pemphigus Foliaceus*
Cytologic examination of an intact pustule (Tzanck preparation) can be a useful in-clinic diagnostic test for tentatively
diagnosing pemphigus foliaceus pending biopsy and histologic examination results. Cytologic examination of an intact pustule
in pemphigus foliaceus shows nondegenerate neutrophils with acantholytic keratinocytes (Figure 8). The cytologic absence of bacteria makes bacterial skin infection a less likely cause of the clinical signs. Since some
cases of superficial pustular drug reactions and dermatophytosis can have similar cytologic findings to those of pemphigus
foliaceus, biopsy and histologic examination are still recommended before treatment of pemphigus foliaceus.
8. Cytologic examination of an intact pustule from a dog with pemphigus foliaceus showing rafts of acantholytic keratinocytes
(arrows) and many nondegenerate neutrophils (Diff-Quik—Dade-Behring; 1000X).
No hematologic changes are specific to pemphigus foliaceus. Dogs can have a mild to moderate leukocytosis with neutrophilia
and a mild to moderate nonregenerative, normocytic, and normochromic anemia (anemia of chronic disease).5 Cats can have similar changes in addition to basophilia, eosinophilia, lymphopenia, and monocytosis.15 In cats, no association exists between feline leukemia virus or feline immunodeficiency virus and pemphigus foliaceus. While
a complete blood count and serum chemistry profile cannot diagnose pemphigus foliaceus, they can help diagnose any concurrent
systemic diseases that could be exacerbated by immunosuppressive therapy for pemphigus foliaceus. Blood work is also recommended
to establish baseline values before starting immunosuppressive treatment. An antinuclear antibody test is not necessary in
cases of suspected pemphigus foliaceus.
Biopsies should ideally be performed on pustules. Micropustules can be present under crusts and, thus, visible on histologic
examination. For this reason, if an intact pustule cannot be found, biopsy of a crust is another option. To avoid disrupting
pustules or crusts, do not scrub the biopsy site. Instead, gently clip the biopsy site while avoiding the removal of surface
crusts. The biopsy site can then be gently blotted with alcohol.
Biopsy results are more likely to be diagnostic if glucocorticoids, both topical and systemic, are discontinued before biopsy.15 We recommend discontinuing glucocorticoids for at least one week before biopsy. Submit samples to a dermatopathologist along
with a complete history and description of the clinical lesions. The distribution of the lesions is also important. A listing
of dermatopathologists can be found online on the Veterinary Information Network (http://www.vin.com); search for "dermatopathologist registry") or by contacting your local dermatologist. Allow the dermatopathologist to perform
PAS stains so that the biopsy can be evaluated for pustular dermatophytosis.
9. Histologic examination of pustule obtained by skin biopsy from a cat with pemphigus foliaceus reveals subcorneal acantholytic
keratinocytes and neutrophils (hematoxylin-eosin; 20X).
Histologic examination demonstrates predominantly superficial, eosinophilic, or neutrophilic pustules with acantholytic keratinocytes
(Figure 9). Rarely, early cases of pemphigus foliaceus can show eosinophilic pustules with spongiosis (intercellular edema) in the
epidermis or around hair follicles but no acantholysis.47
When bacterial skin infections (impetigo and exfoliative pyoderma) are present with pemphigus foliaceus, it can be difficult
to determine which histologic changes are due to the pemphigus foliaceus and which changes are due to bacteria. In general,
pemphigus foliaceus is more commonly associated with a greater density of acantholytic cells and large pustules that span
across multiple hair follicles compared with bacterial skin infections.38 Treat any concurrent bacterial infections with antimicrobials before biopsy to increase the chances of a clear diagnosis
from histologic examination. If you receive a skin biopsy report that lists both bacterial skin infection and pemphigus foliaceus
as possible diagnoses, a practical next step is to treat the possible bacterial skin infection with antimicrobial therapy.
Bacterial culture of the skin may be necessary to select an appropriate antibiotic. Full resolution of lesions with only antimicrobial
therapy is consistent with a bacterial skin infection rather than pemphigus foliaceus.
Systemic immunosuppression is not recommended without a firm diagnosis of pemphigus foliaceus. If a patient is suspected of
having pemphigus foliaceus but diagnostic test results are inconclusive, additional biopsy of other lesions or, preferably,
referral to a dermatologist is recommended.
Immunofluorescence testing is used primarily for research purposes to characterize the immunologic response in pemphigus foliaceus.
The identification of intercellular epidermal IgG via direct immunofluorescence is not specific to pemphigus foliaceus in
dogs.4,14 Indirect immunofluorescence identifies circulating autoantibodies but is highly dependent on the substrate. Immunofluorescence
is not necessary to clinically diagnose and manage patients with pemphigus foliaceus.