Pemphigus foliaceus (PF) is a type of autoimmune skin disorder. With this disease, antibodies produced by the immune system combine with the action of white blood cells to damage the "glue" that holds epidermal (skin) cells together. The skin cells fall apart due to damage caused by the accumulation of white cell “pus” in the skin layers.
Pemphigus foliaceus has been recognized in pet dogs, cats and horses and is the most common autoimmune skin disease diagnosed in veterinary medicine. Pemphigus foliaceus in animals produces clusters of small vesicles that quickly evolve into pustules. Pustules may rupture, forming erosions or become crusted. Left untreated, pemphigus foliaceus in animals is life-threatening due to severe damage to the skin and secondary infection.
Pemphigus vulgaris is a very rare disorder described in pet dogs and cats. Paraneoplastic pemphigus has been identified in pet dogs.
What causes pemphigus?
Most cases of pemphigus in dogs and cats are spontaneous with no known reason for occurrence of the disease. A small number of cases of pemphigus are caused by a reaction to a drug (a type of drug allergy). Some types of cancer of the stomach, intestines, liver, or pancreas are associated with pemphigus in humans. These types of pemphigus, called paraneoplastic pemphigus, appear to be rare in dogs and cats.
What other diseases look like pemphigus?
Skin infections such as bacterial pyoderma or bacterial folliculitis can produce skin lesions that look very much like PF. Microscopic examination (cytology) of material from the lesions can usually determine whether bacteria are present. Dermatophytosis ("ringworm" infection) caused by the organism Trichophyton can mimic lesions of PF to such a high degree that a biopsy, along with culture for this organism, may be needed to differentiate the two diseases. Additionally, a disease called superficial necrolytic dermatitis may cause lesions that are almost identical to pemphigus. The distinction must be made by biopsy and histopathology. (Superficial necrolytic dermatitis is often associated with hepatocutaneous syndrome, which is skin disorder related to a type of liver disease seen in dogs.)
Are there other types of pemphigus than foliaceous?
Yes, two other diseases are seen in animals: pemphigus erythematosus and pemphigus vulgaris. The lesions of pemphigus erythematosus are similar to those of pemphigus foliaceus, but are present only on the head, face, and ears. Pemphigus vulgaris, a disease that can be more serious than PF, is fortunately less common. Pemphigus vulgaris usually produces lesions inside the mouth in addition to those on the skin.
How is pemphigus foliaceous diagnosed?
Pemphigus diseases are diagnosed by a combination of dermatologic examination: patient history, the visual appearance of the lesions, the location of the lesions, microscopic examination (cytology) of material collected from the lesions, and ruling out other diseases that can produce lesions similar to PF. A definitive diagnosis of PF requires examination of high quality skin biopsy specimens by a veterinary pathologist with training in skin disorders (veterinary dermatopathologist).
What is the treatment for pemphigus?
The only chance for improvement is by starting therapy with medications to suppress the immune system. Normally, corticosteroids such as prednisone are used with or without other immunosuppressive medications such as azathioprine or chlorambucil. All these medications have potentially serious side effects requiring monitoring of patient blood work during therapy. If there is a suspicion that pemphigus may have been induced as a reaction to some medication, the suspected medication is discontinued. Newer treatments for autoimmune skin disease, such as intravenous immunoglobulins and photopheresis, are very costly or unavailable for veterinary patients.
What is the prognosis for pemphigus foliaceous?
The prognosis for PF can be poor except for very mild cases. If left untreated, the pet loses body fluids and electrolytes from the damaged skin, develops secondary bacterial infections, fever, and systemic illness. The end result is a seriously ill pet with painful skin lesions. Many cases of PF are difficult to control without the pet and owner having to endure serious medication side effects. It is difficult to predict how well an individual pet suffering from PF will respond to therapy. I have had some cases that presented with very severe skin lesions respond rapidly to therapy, while other patients with less severe symptoms responded poorly to similar doses of the same medications. How well an individual responds to therapy does not appear to be predictable for PF and depends on the ability of medications to suppress the individual animal's immune system, thereby preventing further lesion development and enabling healing of lesions that are present. Another important factor is how well an individual tolerates the side effects of medications. Once the disease is definitively diagnosed, aggressive therapy is started to halt the disease. Dosages of medications are adjusted carefully to reduce side effects while discouraging the return of skin lesions. Many dermatologists feel that pemphigus is more difficult to control if a relapse occurs, so care is taken to reduce medication dosages gradually. Some animals do not respond to therapy at dosages of medications associated with tolerable side effects. Hopefully, a balance between harmful medication side effects and the disease itself is achieved with adequate control.