Previously, differentials of feline facial pruritus were discussed to include ectoparasites such as flea allergy, otodectes,
Notoedres and cheyletiella, food allergy, atopy including possible food storage mite allergy and demodicosis. Less common
differentials include infections such as dermatophytosis, viral, and bacterial pyoderma, Malassezia dermatitis, Pemphigus
foliaceus (PF) and idiopathic facial dermatitis of the Persian cat. Clinically, many of these diseases appear similar including
Pemphigus foliaceus and bacterial pyoderma which can be difficult to differentiate both clinically and histopathologically.
DVM, Dipl. ACVD
Dermatophytosis in cats may have many different presentations ranging from deep crusting lesions to miliary dermatitis to
asymptomatic (Photo 1). It is thought to be more common in younger cats. We probably all should be performing more fungal
cultures than we normally do. To rely on the Wood's light is to gain a false sense of security as more fungal species do not
fluoresce than do. Also normal "scale" may light up under the Wood's light, yet an apple-green fluorescence is what is considered
positive in dermatophytosis with Microsporum canis. Before using the Wood's light, it is important to allow the light to warm
up for five to 10 minutes or a false negative result may occur. False negatives may also occur if iodine shampoos or topicals
have been applied to the cat.
DermatophytosisOther methods of diagnosing dermatophytosis include a trichogram (examination of hairs in oil under the microscope looking
for fungal elements in the hair shaft), fungal culture using the Mackenzie technique of using a toothbrush to comb the cat
for a five-minute period then implanting the hairs/bristles into the fungal culture medium, and skin biopsies with PAS or
GMS stains. Fungal cultures should be kept in a dark, humid place and examined within a 10-day period. If positive, cultures
should be submitted to the lab for identification to be sure dermatophytosis is present and not contaminants that may register
a false positive. Therapies for dermatophytosis have been discussed at length in the past. Topical therapy alone to clinically
affected focal areas can give a false sense of security as other areas of infection may be brewing, yet those areas are not
being treated. I prefer systemic antifungals such as Fulvicin P/G 5mg/kg bid or Fulvicin U/F 30mg/lb bid or Itraconazole 5-10mg/kg/day
along with weekly lime sulfur dips and treatment of the environment.
Photo 1: Perioral dermatophytosis lesions in a cat. Remember some cats with dermatophytosis have no visible lesions.
Isolation of the affected cat is imperative. Liver enzymes need to be monitored with Itraconazole use as does complete blood
counts with Griseofulvin for idiopathic pancytopenia particularly in FIV positive cats. Lufenuron has been published to be
effective for dermatophytosis, yet personal experience suggests unreliable results. A series of two negative fungal cultures
after treatment to ensure the patient's dermatophyte problem has resolved is important.
Bacterial pyodermaBacterial pyoderma in the cat is certainly not as commonly diagnosed as in the dog, but is still a differential to consider
in feline facial pruritus (Photo 2). Staphylococcus simulans is a normal staph resident of feline skin. Staphylococcus aureus
has been identified in cats with pyoderma lesions. The patients are usually older cats and lesions may consist of epidermal
collarettes or deep pyoderma with draining tracts. In the few cases reported, response to antibiotic therapy was important
in making the diagnosis. Other diagnostics included skin biopsies which yielded a neutrophilic folliculitis, perifolliculitis
or panniculitis. Certainly, ectoparasites and dermatophytosis must be ruled out before the diagnosis of a primary bacterial
pyoderma can be made.
Photo 2: Nonhealing bacterial pyoderma in an FIV-positive cat.
VirusesViruses are important pathogens in respiratory infections in cats, yet rarely cause skin lesions. Viruses that can affect
the skin in cats include feline poxvirus, herpes and calicivirus. These organisms can cause skin lesions as well as mucous
membrane lesions. Skin biopsies and PCR testing can be helpful in achieving the diagnosis. Therapy consists of antibiotics,
antivirals, lysine or interferon. In nonhealing skin wounds, the FeLV and FIV status of the patient should be determined.
Photo 3: Idiopathic Facial Dermatitis of the Persian Cat. Note the excessive black material in the facial folds.
Malassezia infectionsMalassezia infections in cats particularly affecting the facial folds may play an accompanying role in idiopathic facial dermatitis
of the Persian cat (Photo 3). Affected cats have marked dark material deposited in the facial folds sometimes accompanied
by erythema, ulceration, otitis and blepharitis. Malassezia yeast is sometimes isolated and treatment with antiyeast medications
may help in some patients. Others may have secondary bacterial involvement, yet antibiotics may only produce partial resolution.
Skin biopsies yield acanthosis, hydropic degeneration with dyskeratotic basal cells, sebaceous hyperplasia, with a mixed diffuse
inflammation. Therapies have included systemic steroids, oral antifungals, hypoallergenic diets and oral cyclosporine. Unfortunately
the etiology is unknown and the disease may be genetic. Included in Malassezia problems in cats is a yeast otitis/dermatitis
particularly of the chin. It is possible that when the cat is grooming itself, it transfers yeast from the ears to the chin/lipfold
area. Anti-yeast otic preparations along with oral ketoconazole or itraconazole may be helpful.
Photo 4: Crusting of the dorsal nose in a cat with pemphigus foliaceus.
Although most veterinarians consider pemphigus foliaceus (PF) to be rare, it is actually not uncommon to see this disease
in cats with a facial dermatitis. Up to 80 percent with facial lesions of PF have been reported to be pruritic. Lesions may
include crusting of the ear pinna, face, surrounding the nipples and nailbeds. Cats of any age may be affected (Photo 4).
The patient may be febrile and have a leukocytosis, eosinophilia and/or mild anemia. On cytology of the lesions, acantholytic
cells along with neutrophils or eosinophils may be present. In a referral practice, the history includes that the patient
was initially responsive to steroid injections, and they are referred usually because of steroid tolerance. Skin biopsies
are necessary to make the diagnosis, and it is helpful to have the patient as long off steroid as possible to obtain an accurate
histopathological diagnosis (Photo 5). Skin biopsies of the crusts or if present, an intact pustule, should be submitted in
10 percent formalin along with a thorough history. Histopathological findings include subcorneal pustules composed of neutrophils,
eosinophils and acantholytic cells and perivascular to interstitial inflammation consisting of neutrophils and mast cells
(Photo 6). Pustules may span several follicular units. Fungal cultures must also be performed to rule out dermatophytosis
since some fungal species produce acantholysis. Treatment of PF includes oral steroids such as prednisolone, methylprednisolone,
triamcinolone or dexamethasone initially to get the disease into remission. Reduction or withdrawl of steroids is the ultimate
goal since they may incite diabetes in the cat if used long term. The addition of Chlorambucil 0.2mg/kg qod may be needed
in some patients who cannot be weaned off steroids.
Photo 5: Multifocal erythema/crusting on the face of the cat with pemiphigus foliaceaus.
Pemphigus foliaceusWith the use of Chlorambucil, complete blood counts need to be routinely checked for reduction of red blood cells, white blood
cells and platelets. Other therapies include doxycycline 5 mg/kg bid which may have some activity in autoimmune disease and
sunlight avoidance. Sun, at least in human autoimmune diseases, can cause a flareup of the disease. Unfortunately it is not
known what triggers the autoimmune reaction of the adhesion between the epithelial cells which defines PF, but factors such
as medications, vaccinations, insect bites or underlying neoplasia may play a role in some patients.