What autoimmune diseases can affect dogs?

 

Pemphigus foliaceus


Autoimmune diseases that lead to visible skin changes can either only affect the skin / mucous membranes or the skin and other organ systems.

In dogs, the most common of these autoimmune diseases are pemphigus foliaceus (PF), discoid lupus erythematosus (DLE) and pempigus erythematosus (PE), more rarely bullous pemphigoid, pemphigus vulgaris and systemic lupus erythematosus (SLE).

In autoimmune diseases, the immune system fails to recognize what its own and foreign structures are in the body; humoral (affecting the hormonal system) or cellular (affecting the cells) antibodies are directed against the body's own cells or cell structures.
In general, as a dog gets older, the tendency to develop such an autoimmune disease increases. The reasons for this are to be found in a loss of efficiency in immune monitoring, a loss of immune tolerance and cross-reactions between autoantigens and foreign antigens.

Statistically speaking, pemphigus foliaceus is the most common autoimmune disease in dogs, but with around 0.5% - 0.68% of dermatological cases, pemphigus diseases are rather rare. The statements as to whether there is a real breed disposition for pemphigus foliaceus or not are inconsistent. Sources give such for the Akita Inu, Doberman, Newfoundland, Bearded Collie, Schipperke, Finnenspitz, Chow-Chow and Dachshund. The possibility of a genetic predisposition is suspected.
In about 50% of pemphigus foliaceus cases, the disease develops before the age of five, the first symptoms appear on average at the age of four.

It is possible to differentiate pemphigus foliaceus disease into three different forms:

  • spontaneous pemphigus foliaceus, mainly observed in Akita Inu and Chow Chow with a presumably hereditary (hereditary) component

  • Drug-mediated pemphigus foliaceus, increasingly found in Labrador Retrievers and Pinschers, i.e. hypersensitivity to a drug. After stopping the corresponding medication, there is usually a spontaneous remission (subsidence of the symptoms of the disease)

  • Pemphigus foliaceus in predisposed dogs with a medical history (anamnesis) of long-term chronic skin problems, which is probably also triggered by one of the drugs administered, but spontaneous remission is rather rare here.

In pemphigus foliaceus, blisters form in the upper layers of the epidermis. These vesicles are caused by a loss of intercellular adhesion, i.e. the connection between the cells of this skin layer (kerationocytes = horn-forming cells of the epidermis). These connections are made by adhesive plates (desmosomes), a protein found in them is desmoglein I (desmoglein I only occurs in the skin, not in the mucous membranes).
In pemphigus foliaceus, the immune system forms antibodies against desmoglein I (occasionally also against desmoglein II), and the adhesive plates are destroyed. As a result of the lack of cell cohesion, the keratinocytes that have become free are rounded off (this process is called acantholysis).

Fissures and then bubbles with a diameter of one to ten millimeters form within the epidermis. Since dogs have a very thin epidermis, the pustules burst and dry up quickly, a typical honey-colored crust forms (secondary lesion), under which there is often a moist surface. The pustules can form on hair follicles as well as non-follicular. If follicles are involved, it can lead to hairless areas that are surrounded by crusts and scallops. Coming and going of the lesions is typical, the general condition of the dogs is usually good at first, in rare cases systemic symptoms such as fever, decreased liveliness, lameness, swelling of lymph nodes (lymphadenopathy) and deposits of fluid in the tissue (edema) have been observed. The itching is very different, but it can be very intense.

An exacerbation (marked worsening of the symptoms of an already existing, usually chronic disease) was often observed during the summer months. In the specialist literature, the case of a dog suffering from pemphigus folicaeus is described in which unaffected areas of the skin were selectively exposed to UV radiation. In this dog, the acantholysis described above could be triggered (induced) on the areas of skin that were irradiated in this way.

In the dog, the skin areas in which there is a particularly large amount of desmoglein I in the epidermis are initially affected, especially the head area and here the area of ​​the nose, the bridge of the nose, the area around the eyes and the auricles. Other frequent locations are the paws, on the claw bed and on the balls of the feet, where fissures, hyperkeratosis (excessive cornification, often also found on the nasal surface) and ulcers occur. In the further course of the disease, the pemphigus foliaceus may generalize and spread to other parts of the body (abdomen, back), often accompanied by a disturbed general condition, secondary infections (bacteria) of the affected areas of the skin may occur.

If pemphigus foliaceus is suspected, it is possible to specifically open pustules and examine them cytologically; acantholytic cells can be visualized in this way. This is often difficult due to the fact that the pustules are only a very short-lived phenomenon.An attempt can also be made to remove crusts and then place a slide on the exposed exudate (secretion of protein-rich fluids as part of inflammatory processes). In this way, cytologically, the very small, rounded keratinocytes, just as well preserved, segmented granulocytes and occasionally eosionophilic granulocytes can be recognized.

However, a reliable diagnosis is only possible through the histopathological examination of skin biopsies; pustules are also best suited for this. Direct or indirect immunofluorescence tests (IF) for the visualization of antibody deposits in the intercellular spaces are rarely used in veterinary medicine due to numerous incorrectly interpreted results. In special laboratories, antibodies in the intercellular spaces can be stained using immunohistochemical techniques, a clear and reliable method.
In dogs with pemphigus foliaceus, an ANA test (serological test for antinuclear antibodies) is usually negative, routine laboratory tests are usually normal, but leukocytosis (up to 80,000 / mm³) is not unusual and around 15% of dogs are peripheral Eosinophilia (an increase in the number of eosinophilic granulocytes).

Therapy for pemphigus foliaceus is usually a lifelong, immunosuppressive treatment. In about half of the affected dogs, remission (temporary or permanent weakening of the symptoms in chronic diseases without a cure being achieved) can be achieved by administering prednisone alone, the other half of the patients require combination therapy such as prednisone and azathioprine (or Prednisone with chorambucil or chrysotherapy, the use of other glucocorticoids such as dexamethasone or triamcinolone is also possible. Combination treatment usually results in more side effects (glucocorticoid in connection with azathioprine, for example iatrogenic hyperadrenocorticism, hepatotoxicity, anemia, demodicosis and gastrointestinal bleeding).


The information on the level of initial prednisone / prednisolone administration in the literature varies greatly, the information ranges from 1-2 mg / kg body weight twice a day to 2 mg / kg / day up to 2-6 mg / kg / day. The best known side effects of high-dose glucocorticoid therapy are polydipsia (excessive fluid intake) and polyuria (increased urine excretion), weight gain and increased panting. If these side effects become too severe, the combination with azathioprine, for example, can be useful in reducing the glucocorticoid. Important side effects of azathioprine are thrombocytopenia (lack of blood platelets), leukopenia (lack of white blood cells) and anemia (anemia, lack of red blood cells, the oxygen-carrying capacity of the blood is reduced).
A three-day high-dose steroid pulse therapy, i.e. cortisone shock therapy, is also possible as an introduction to drug treatment. In two Akitas with pemphigus foliaceus this was carried out with methylprednisolone succinate 10 mg / kg / day for 1 hour i.V. on three consecutive days. Oral treatment with azathioprine and prednisolone was continued.
As soon as the course of the disease allows, the immunosuppressive drugs are reduced to the lowest possible maintenance dose.
Additional local treatment of the affected skin areas is indicated as an accompanying therapy, often with cortisone creams. Studies have also shown good success with the relatively new active ingredient topical 0.1% tacrolism ("Protopic"); the side effects seem to be significantly lower compared to the corticosteroids. However, the costs for Protopic are relatively high in comparison, the preparation is quite economical due to its tough, well-adhering consistency.

At the clinic for small animals of the University of Veterinary Medicine Hannover, there was a case of a Kromfohrländer bitch with pemphigus foliaceus with secondary pyoderma, which did not respond permanently to any drug therapy. Since the lesions in this case were limited to the neck, croup and tail base area, the entire changed skin areas were finally surgically removed. There was no subsequent drug therapy; a period of 24 months postoperatively has been documented as free of recurrences.


 

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