Pemphigus in dogs – blisters, crusts and autoimmune skin disease

Overview

Autoimmune skin disease means that a normally protective immune response starts damaging the dog's own tissues. In pemphigus foliaceus, superficial pustules rupture quickly, so crusts are often more evident than intact blisters at the appointment.

The disease may be limited to the face, footpads or body, but can also become widespread. Pemphigus vulgaris is a rarer, deeper form that particularly damages the mouth and the junctions between skin and mucous membranes.

Pemphigus erythematosus is generally considered a milder form of foliaceus. Paraneoplastic pemphigus is an exceptionally rare form associated with an underlying tumour.

The names of these blistering disorders therefore describe different tissue damage, and the outlook and distribution of signs are not the same for every form.

Causes

The connections between skin cells fail

Keratinocytes, the skin's surface cells, attach to one another through structures called desmosomes. In pemphigus, autoantibodies that bind to skin cell structures are associated with the cells separating from one another.

This separation is called acantholysis and allows a blister to form within the skin layers. Antibodies against an attachment protein called desmocollin-1 have been identified in more than 80% of dogs with pemphigus foliaceus.

However, the precise role of these antibodies in causing damage is still partly unresolved. In most dogs, the initial trigger for the disease is not identified.

In some cases, onset has coincided with medication, but a link in timing alone does not prove that the medicine caused the disease. The target of the antibodies and its location within the skin influence whether superficial skin changes or deeper mucosal damage develops.

Risk factors

Pemphigus foliaceus can develop in any breed, including crossbreeds. Akitas and Chow Chows are over-represented among patients, supporting the possibility of an inherited predisposition.

Reported median ages at onset are around 4 and around 6 years, so this is often a disease of middle-aged dogs. However, it can start at any age, and the usual age estimates do not rule it out in a young or old patient.

No clear sex predisposition has been identified. Chronic allergic skin diseases have been described in the same patients, but a causal relationship between allergy and pemphigus is uncertain.

Typical symptoms

Signs may appear in waves as new blisters develop and earlier ones become crusted areas.

• Lesions often develop on both sides of the bridge of the nose, the nose itself, around the eyes or on the ear flaps.

• Thin-roofed pustules form on the surface and rupture easily.

• Thick layers of yellowish crust build up on the skin.

• A superficial erosion may be visible beneath a crust, and hair may be missing from the affected area.

• Thick crusts cling to the edges of the footpads, sometimes without visible skin changes elsewhere.

• Itching ranges from mild to severe.

An individual pustule can span several adjacent hair follicles. Pemphigus foliaceus usually spares the lining of the mouth, so mouth ulcers prompt investigation for other disease forms too.

Oral lesions have been described in more than 90% of dogs with pemphigus vulgaris. In around 6% of vulgaris patients, signs have been limited to the oral cavity alone.

Mouth pain may show as drooling, bad breath and lip-smacking.

Complications and consequences

A damaged skin surface predisposes to secondary bacterial infection, which can increase tenderness and discharge. Widespread pemphigus may be accompanied by fever, weight loss and reduced appetite.

Treatment side effects can be as significant as the skin disease, so the aim is a good quality of life for the dog. In different groups of dogs with pemphigus foliaceus, 7–42% have been euthanased.

Decisions to euthanase have been influenced by uncontrolled disease, treatment side effects, quality of life and the owner's ability to carry out treatment. These figures do not represent direct mortality from the disease alone, as they include factors relating to treatment and euthanasia decisions.

The long-term prognosis for pemphigus vulgaris is guarded to poor, and it can be fatal without treatment.

Diagnosis at the vet

Cytology helps; a biopsy confirms

The medication history, progression of skin changes and response to earlier treatment are reviewed before sampling. A cytology sample is preferably taken from an intact pustule or beneath a fresh crust.

The sample is examined for skin cells that have separated from one another and the inflammatory cells surrounding them. Acantholytic skin cells have been obtained on cytology in around 77% of dogs with pemphigus foliaceus.

Similar detached cells can also occur with bacterial infection, ringworm or leishmaniosis. Concurrent bacterial or fungal disease is therefore investigated separately, for example using cytology and culture.

Confirmation usually requires histopathological examination of skin biopsies, meaning assessment of the tissue structure. Several fresh lesions are usually selected, for example 3–4 representative samples.

A sample may be collected with a biopsy punch around 6–8 millimetres in diameter or by cutting out a suitable piece of skin. The sampling site is not scrubbed clean, as an intact blister and crust layer can contain the crucial findings.

Any immunosuppressive medication is taken into account when sampling because it may make the changes harder to demonstrate. Special tissue stains can help detect bacteria or fungi that are not clearly visible on routine examination.

In selected situations, immunofluorescence can assess the presence and location of antibodies targeting the skin. If antibiotics have already been used, culture and susceptibility testing of discharge can guide treatment of any secondary infection.

Tissue samples distinguish other autoimmune diseases

In pemphigoid, a blister forms beneath the surface skin layer when antibodies target its attachment to the basement membrane. Cutaneous lupus, meanwhile, may begin particularly with loss of pigment, redness and scaling of the nose.

If the biopsy suggests paraneoplastic pemphigus, an underlying tumour is sought through a thorough examination and imaging of the chest and abdomen.

Treatment

The immune response is suppressed through a planned approach

Your vet prescribes treatment and medication according to the form and extent of the disease and your dog's general health. Initially, the aim is to prevent new lesions and allow existing damage to heal.

A systemic glucocorticoid is most commonly used to suppress the harmful immune response. A topical corticosteroid may suit limited lesions or supplement other treatment.

Combination treatment may include azathioprine, ciclosporin or mycophenolate mofetil, for example, to reduce the need for corticosteroids. Drug choice also depends on the dog's ability to tolerate treatment and the feasibility of monitoring side effects.

Before substantial medication is started, a blood count, blood biochemistry and urinalysis are usually performed to assess the dog's baseline condition. Early in azathioprine treatment, blood values may be checked every 2 weeks to detect bone marrow and liver effects.

Long-term corticosteroid treatment can cause muscle wasting, skin thinning, diabetes and increased susceptibility to infection. Ciclosporin can cause digestive upset and sometimes gum overgrowth or opportunistic infections.

Diarrhoea is a common side effect of mycophenolate, so digestive signs are also recorded during monitoring. An antibiotic is needed for an identified secondary infection, but does not prevent the pustules caused by pemphigus itself.

Topical treatment is the first choice for antibacterial treatment of a superficial bacterial infection where appropriate. Antiseptic washes planned by the vet can soften crusts and discharge and improve comfort alongside other treatment.

Corticosteroid medication can markedly increase drinking and urination, which is important to distinguish from signs of the skin disease itself. Long-term glucocorticoid treatment can also cause calcium deposits in the skin, called calcinosis cutis.

Potential serious glucocorticoid side effects also include gastrointestinal ulceration, which is considered during treatment monitoring.

Response and maintenance treatment

Skin lesions often settle within around 4–7 weeks. However, gaining control of canine pemphigus can be slow: reported times with different treatments have ranged from 1–36 months.

Your vet may consider reducing treatment when no new lesions have appeared for at least 2 weeks and around 80% of previous lesions have healed. Medication is reduced individually, as reducing or stopping it too quickly can bring signs back.

Most dogs need long-term or lifelong treatment, even if maintenance treatment is less intensive than the initial phase. A small, occasionally recurring lesion may sometimes be accepted if stronger immune suppression would cause the dog greater harm.

Prevention

The trigger usually remains unknown, so practical, cause-specific prevention is unavailable for most cases. If a particular medicine is suspected as a trigger, future use is avoided according to the treating vet's plan.

Avoiding strong sun may help, as sunlight has been suspected of worsening pemphigus foliaceus. During substantial immunosuppressive treatment, the vaccination plan is assessed individually, with specialist input if needed.

Your dog's vaccinations are planned alongside the other treatment; do not change them or the immunosuppressive medication yourself.

Important for dog owners

Photograph the face, ear flaps, footpads and other affected areas under the same lighting conditions. Record new blisters, the amount of crusting, pain and itching. Note appetite, drinking, urination, stools and movement to help distinguish the effects of the disease from those of medication.

Bring the complete medication list to the appointment, including parasite treatments and topical products. Explain what was used before the first signs and what was only started afterwards. Before the sampling appointment, check whether you may wash or treat the skin.

Keep a written treatment plan and follow-up dates. Do not stop a corticosteroid suddenly or alter combination treatment yourself. If giving medicines or attending monitoring appointments is difficult, tell the veterinary team so the plan can be adapted to everyday life. Mouth pain, refusal to eat and extensive skin damage need prompt reassessment.

Frequently asked questions

Can pemphigus spread to another dog?

The underlying mechanism of pemphigus is an immune reaction against the dog's own skin, rather than an infection passed between dogs. However, a secondary bacterial skin infection can develop and is investigated and treated separately. Skin changes in other animals sharing the home need their own diagnosis: crusts alone do not mean the same disease.

Why does an antibiotic not remove all the crusts?

Pemphigus lesions result from damage to the attachments between skin cells, so an antibacterial medicine does not correct the main disease mechanism. Treating a concurrent infection also does not stop new pemphigus pustules forming. Control of the disease itself relies on suppressing the immune response through a veterinary plan. The plan is tailored to the circumstances of the patient and owner.

Is cytology enough for a diagnosis?

Cytology can raise a strong suspicion, but detached skin cells also occur in certain infections. A definite diagnosis usually requires examination of a representative skin biopsy. Sample selection, investigation of other diseases and the full clinical picture are considered together before long-term immunosuppressive treatment starts.

Can medication stop when the skin looks healthy?

Most dogs with pemphigus foliaceus need long-term treatment even when they have no signs. Signs may recur when medication is reduced or stopped. Treatment is reduced according to a written plan and skin monitoring. Contact your vet before withholding medicines.

Are mouth ulcers part of the usual form of pemphigus?

The most common form, foliaceus, usually spares the lining of the mouth. Oral blisters and ulcers are common in the vulgaris form, however. Pemphigoid and other immune-mediated diseases can also cause oral signs. Mouth pain, drooling or difficulty eating are therefore reasons to have your dog examined promptly.