Pemphigus complex is a group of rare bullous autoimmune diseases in cats. These type of diseases are the result of an overactive immune response against the cat’s own tissues. This leads to an overproduction of autoantibodies which attack the epidermal adhesion molecules causing them to separate, resulting in the formation of superficial vesicles and bullae (a blister which contains serous fluid) which rupture to form crusted erosions on the skin.
The cause isn’t known exactly, but it has been suggested there could be a genetic predisposition, or caused by exposure to sunlight, certain drugs such as cimetidine and ampicillin, history of chronic inflammatory skin disease.
While the cause may still be undetermined what we do know is that a separation of keratinocytes (epidermal cell) occurs within the stratum corneum (the outermost layer of the epidermis). Autoantibodies attack the desmosomal proteins which are structures that attach the epidermal cells to each other, this leads to skin cells separating and fluid collecting between the separated layers. This is known as acantholysis
The name pemphigus is derived from the Greek word pemphix meaning bubble or blister. There are three types of pemphigus that have been described in cats depending on the location of the vesicles as well as the layer of skin (superficial, middle or deep).
Pemphigus foliaceus (PF) is the most common type, affecting the superficial epidermal layers (the top/outermost layer of the skin).
Pemphigus erythematosus (PE) is the second most common form and is believed to be a milder form of pemphigus foliaceus in which only the head and feet are affected.
Pemphigus vulgaris (PV) is very rare, producing blisters in the deep layers of the epidermis. Lesions typically occur in the mouth and areas of trauma such as claw folds, ears, armpits, and groin. Secondary infections are common and are often fatal.
Pemphigus is known to occur in cats, dogs, humans and horses. In cats, middle aged to older animals are most commonly affected. While pemphigus is a rare condition, it is the most common auto-immune disease to be found in cats.
Is pemphigus contagious to cats and people?
No, it is not possible for cats or people to catch pemphigus as it is an immune disorder.
Symptoms of pemphigus complex in cats
The most common symptoms of pemphigus complex are fluid-filled pustules. These eventually break open and then form a dry crust. It is also possible for symptoms to wax and wane over time.
The distribution of small red spots and hair loss can be found, starting around the eyes and the bridge of the nose, before spreading to the ears, neck, nail beds, on and around the food-pads, nipples, and groin. Small areas of skin discolouration occur before fluid-filled blisters form just beneath the surface of the skin, these rupture to form a yellowish crusting erosion.
As the ears become affected, inflammation (otitis externa) can develop.
Affected areas are painful and itchy.
Lameness if the feet are affected.
Secondary bacterial infection may also be present.
Symptoms are similar to that of pemphigus foliaceus, however, symptoms are generally milder and confined to the head and feet only.
Pustules are limited to the head and feet. Red and inflamed crusting areas with hair loss.
This is the most severe form of pemphigus with blisters forming in the deep epidermal layers of the skin.
Affects the mouth, claw folds, ears, armpits (axilla) and groin. These vesicles are easy to rupture and when they do, deep ulcers form.
Vesicles are itchy and painful.
Anorexia (loss of appetite) due to painful ulcers in the mouth.
Secondary bacterial infection is common with this form of pemphigus.
Diagnosis of pemphigus complex in cats
Your veterinarian will perform a physical examination of your cat and obtain a medical history from you including how long symptoms have been present, any other medical conditions your cat may have and any medications he is currently taking.
Diagnostic tests are necessary to confirm diagnosis as symptoms of pemphigus may be similar to that of dermatophytosis (ringworm), demodicosis or paronychia.
A blister biopsy will be collected by a ‘punch tool‘ (which penetrates all the layers of the skin) and examined under the microscope. Separated/free floating detached epidermal cells (known as acantholytic keratinocytes) will be seen. The biopsy will also determine which layer of skin is involved. Multiple samples may be required.
Direct immunofluorescence to look for the presence of antibodies.
Cytological examination of an intact pustule which may reveal nondegenerative neutrophils, with acantholytic keratinocytes.
Your veterinarian may also perform a bacterial culture of the sample to look for secondary bacterial infection.
Routine screening including biochemical profile, complete blood count, and urinalysis should also be performed, while these can’t diagnose pemphigus, they are important to check for concurrent systemic disorders which may be affected by immunosuppressive therapy.
Treatment of pemphigus complex in cats
Treatment of pemphigus complex can be quite difficult. It involves immunosuppressive therapy to stop the cat’s own immune system attacking the tissues. Generally, a large dose is initially given to induce remission, due to the potential side effects of these medications, once remission is achieved the dose then be tapered to the lowest possible dose to manage the condition.
Corticosteroid drugs such as prednisone or methylprednisone are the first choice of treatment. Small, localised lesions may be responsive to topical therapy but more widespread cases will require larger immunosuppressive doses to achieve a remission.
If remission is not achieved after 7-14 days with the above medications then other therapies may be added, such as Chlorambucil, a chemotherapy drug or Azathioprine, a chemotherapy and immunosuppressive drug, Cyclosporine an immunosuppressive drug. Again, the dose will be gradually tapered back over time. Side effects can include vomiting, diarrhea and bone marrow suppression.
If your cat is on medications which could have triggered pemphigus, your veterinarian will look for alternatives, if possible.
If bacterial infection is present:
Oral antibiotics may be necessary to treat any secondary bacterial infections.
Topical antiseptics will also be given to treat bacterial infections.
Follow your veterinarian’s instructions carefully and administer all medications as prescribed.
Side effects from the use of immunosuppressive drugs can be severe and close monitoring every 2-4 weeks will be necessary.
It may be recommended that your cat has limited exposure to the sun.
What is the prognosis for cats with pemphigus?
This depends on the type of pemphigus your cat has and how well he responds to treatment.
In cats with drug-induced pemphigus, this should resolve once the medication has been stopped.
Cats with the milder pemphigus erythematosus usually respond well to therapy.
The prognosis is guarded for cats with pemphigus vulgaris.
In most cases (except for drug-induced pemphigus), therapy is lifelong.