A 10-year-old castrated male domestic shorthair cat was presented with a short history of severe and acute crusting dermatitis, affecting the face, ears and feet. The cat had no previous history of skin disease, it had a normal appetite and was not pruritic.
The general physical parameters were within normal limits. A dermatological examination revealed:
- Symmetrical distribution of scaling, crusting, erosions and alopecia, both on the nose and above the eyes (Figure 1)
- Thick adherent crusts, papules, pustules, erythema and erosions present on the concave and convex aspects of the ear pinna (Figure 2)
- The nail beds of all four feet contained thick caseous purulent exudate
Differential diagnosis
- Pemphigus foliaceus
- Bacterial pyoderma
- Dermatophytosis
- Cutaneous adverse drug reaction
- Erythema multiforme
Initial investigations
- Skin scrapes failed to reveal any ectoparasites
- Hair plucks showed no evidence of arthrospores or infected hairs
- Wood’s lamp examination was negative for fluorescence
- An impression smear from the surface of the skin where the crust was lifted, stained with modified Wright’s stain (DiffQuik) revealed numerous nondegenerate neutrophils and acanthocytes (Figure 3)
These findings supported the diagnosis of pemphigus foliaceus.
Further investigations
Skin biopsies were harvested to confirm the diagnosis. The histopathological findings consisted of sub-corneal, intragranular, or follicular, pustules with acanthocytes and non-degenerate neutrophils with varying degree of epidermal acanthosis and surface crusts. These findings supported the diagnosis of pemphigus foliaceus.
Diagnosis
Pemphigus foliaceus.
Prognosis
The prognosis for pemphigus foliaceus varies between individuals and many cats require lifelong medication. Pemphigus foliaceus may occur spontaneously, or be triggered by drugs, infections and chronic skin diseases, which may have implications for the long-term prognosis. Some animals respond to treatment, but develop severe adverse effects to the treatment itself. It is therefore necessary to monitor all cases, both during the induction and the maintenance phases.
Treatment
Treatment is divided into induction and maintenance phases. The initial drug of choice is oral prednisolone at 4mg/kg to 6mg/kg every 24 hours for 10 to 14 days. The duration of the induction phase varies between individuals with tapering to the eventual maintenance dose once there is clinical resolution of the crusting and erosions. The alopecia may persist at this stage, but provided there are no new lesions being formed, the induction dose can be tapered to the maintenance dose over the following four to six weeks.
The maintenance dose should be the lowest possible alternate day dose that keeps the disease in remission.
Methylprednisolone, at similar dosages, is an alternative to prednisolone.
This cat was treated with prednisolone at 4mg/kg for 10 days, reduced to 3mg/kg for another seven days, and then reduced to 3mg/kg every other day for four weeks. Over the following six weeks, the dose was tapered to 5mg (1mg/kg) every other day; the cat remained in remission at this dose for two years (Figure 4). Attempts to lower the dose further led to relapse. After two years the cat was lost to follow-up.
Some cats may require more potent glucocorticoids, such as dexamethasone or triamcinolone, or other immunosuppressive drugs, such as chlorambucil, to achieve remission. However, the potential adverse effects of these drugs (Table 1) must be borne in mind and the patient monitored accordingly.
Monitoring
Haematological and biochemical profiles, with urinalysis and urine cultures, should be performed at least every six months, or more often as indicated in Table 1.
| DRUG | INDUCTION DOSE | MAINTENANCE DOSE | ADVERSE EFFECTS | MONITORING |
| Prednisolone | 4 to 6mg/kg PO q24h | 1 to 2mg/kg q48h | Polyuria, polydipsia, polyphagia, diabetes mellitus, cystitis, obesity, hepatic and cardiac dysfunction | Every four to six months |
| Methylprednisolone | 4 to 6mg/kg PO q24h | 1 to 2mg/kg q48h | As above | Every four to six months |
| Dexamethasone | 0.2 to 0.4mg/kg PO q24h | 0.01 to 0.05mg/kg q48 to 72h | As above | Every four to six months |
| Ciclosporin | 5 to 7.5mg/kg PO q24h | 5mg/kg q48 to 72h | Anorexia Soft faeces Gingival hyperplasia | Every four to six months |
| Chlorambucil | 0.1 to 0.2mg/kg PO q24h | 0.1 to 0.2mg/kg q24h to 48h | Bone marrow suppression | Every two weeks initially, then every three months |
Discussion
Pemphigus foliaceus is a sterile pustular autoimmune disease, where the IgG autoantibodies target the desmosomal glycoproteins responsible for cell-to-cell adhesion of keratinocytes in the epidermis. Pemphigus foliaceus can be drug-induced or spontaneous. Methimazole, cimetidine, ampicillin, itraconazole and lime-sulphur have all been implicated in triggering the disease. It is suggested that these drugs may activate the proteolytic enzymes in the skin, resulting in acantholysis. In dogs, the autoantibodies target the cell-to-cell adhesion molecules desmoglein-1 and desmocollin-1. The role of desmosomal proteins in feline pemphigus foliaceus is yet to
be determined.
The presence of acanthocytes on cytological examination, a simple in-house technique, supports the diagnosis and rules out other diseases that also cause papulocrustous dermatitis in cats.
Ideally, the best sites to biopsy are papules or intact pustules; however, because they tend to be very fragile and transient, they may not be present. In these cases, biopsies of recent lesions, including the crusts, should be taken for histology. In the absence of pustules, these samples may show rafts of acanthocytes among the surface crust. It is also worth bearing in mind that biopsies from cats suffering from pemphigus foliaceus often also show large numbers of eosinophils.
In a retrospective study, 97 percent of cats with pemphigus foliaceus achieved complete remission with a median induction dose of 2 mg/kg prednisolone daily; 14 percent of these cats went on to recover eventually without the need for further medication, and the remainder remained in remission with alternate day dosing (Simpson and Burton, 2013). Many cats require long-term treatment and therefore monitoring for adverse effects is an essential component of the treatment regime.
