Pemphigus Foliaceus
Also known as: Pemphigus Foliaceous
Introduction
Pemphigus foliaceus is an autoimmune disease in which autoantibodies are directed against components of the epidermis resulting in separation of the epidermal cells (acantholysis) and subcorneal vesicle formation.
It is a pustular skin disease and should be considered in cases which are non-responsive to antibiotics and where pustules are found in areas where staphylococcal pustules are rarely seen (eg the pinnae).
It is more common in dogs than in cats and horses, but is still an uncommon disease.
Pathogenesis
Autoantibodies are directed against a component of desmosomes, which are the main intracellular bridges between the keratinocytes and are responsible for cell-to-cell cohesion. There is loss of cohesion between keratinocytes and there is acantholysis and pustule formation.
A pemphigus foliaceus-like disease can be initiated by drug therapy. If the disease resolves when the drug is stopped it is called 'pemphigus foliaceus-like drug reaction' and if the disease persists after the drug is stopped it is called 'drug-induced pemphigus foliaceus'.
Trimethoprim-sulpha is responsible in dogs, and in cats, doxycycline, ampicillin, cimetidine and methimazole have been implicated.
Clinical signs
The disease is usually of gradual onset and presents as a vesicobullous or pustular dermatitis with secondary erythema, scale, alopecia, erosion and crust formation. Epidermal collarettes are common.
The lesions may be distributed evenly over the body, usually in a symmetrical way, including the pinnae and the bridge of the nose.
Pustular/hyperkeratotic footpads may be seen.
Usually, only the skin is affected and lesions on the mucocutaneous junctions and in the oral cavity are rare.
In cats, lesions tend to be more localised and present on the muzzle, nasal planum, pinnae, around the nipples, in the footpads and in the ungual folds. Malaise, pyrexia and anorexia may also be noted.
Differential Diagnoses
Demodicosis
Superficial pyoderma
Zinc responsive dermatitis
Dermatophytosis
Epitheliotropic lymphoma
Drug eruption
Systemic lupus erythematosus
Diagnosis
The presence of primary lesions (pustules) on the pinnae is of great significance.
A smear can be obtained from the pustule contents using a 25g needle. The underside from a crust can also provide information.
Cytology may reveal: large numbers of non-degenerate neutrophils, variable numbers of rounded keratinocytes (acanthocytes), and minimal or small numbers of bacteria.
There may be a positive Nikolsky's sign, which describes lateral digital pressure on the skin producing erosions.
Histopathology is diagnostic in 80% of cases and helps rule out most differential diagnoses. It may show subcorneal pustular dermatosis.
Demodicosis and dermatophytosis can be ruled out with skin scrapes.
Immunofluorescence can be used in cases where histopathology is not diagnostic.
Treatment
Baseline haematology and biochemistry should be obtained prior to starting any therapy.
Suppression of clinical signs can usually be achieved with immunosuppressive doses of prednisolone. Doses can be increased if there is no response.
Once remission is achieved, the dose can be slowly tapered and nearly half the cases can usually be maintained on alternate-day therapy.
The majority of feline cases response well to prednisolone therapy and can be maintained in clinical remission.
A significant proportion of dogs may fail to respond to glucocorticoid therapy and may require additional drugs.
Azathioprine is a useful steroid-sparing drug in dogs. The beneficial effects may not be apparent for 3-5 weeks.
Azathioprine is contraindicated in cats.
In dogs, side effects include: bone marrow suppression, gastrointestinal effects.
Chlorambucil can be used as a steroid-sparing drug in both dogs and cats. It is sometimes used as a sole agent in cats.
Gold salt therapy can also be beneficial in some cases.
Occasionally, animals treated with immunosuppressive drugs and steroids may develop generalised demodecosis and urinary tract infections, which have to be treated aggressively.
Prognosis
Prognosis for animals which respond to therapy is good, although life-long treatment may be required.
Animals that respond poorly to initial therapy, or require high dosages of drugs to control lesions, have a poor long term prognosis.
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References
Merck and co (2008) Merck Veterinary Manual Merial
Harvey, R. (2009) A colour handbook of skin diseases of the dog and cat Manson Publishing
Hedlund, C. (2002) Clinical atlas of ear, nose and throat diseases in small animals Schlütersche