The immune system is an intricate and dynamic mechanism that acts as both the information-gatherer and the protector of the body from invaders both external and internal. It is like an army, with multiple parts playing integral roles for overall success as measured by prevention of infection. It seems obvious that the immune system is able to identify molecules and organisms that do not belong in the body, and therefore act against them to sequester and remove them. It is less obvious that to do this, the body must know what is normal in the body and what is not.
To emphasize that point, the immune system is one of the body's main defenses against the development of cancer. When the immune system detects that a cell is acting abnormally, for example becoming cancerous, it can destroy the cell, or trigger it to self-destruct. Patients who are immunosuppressed have a higher risk of developing cancer for this reason.
If the body fails to identify a part of body structure as "normal," it may initiate an attack against it. This is called "auto-immune" disease (self-attacking).
Though overall uncommon, there are several auto-immune diseases that affect our companion animals. Many of them appear clinically similar, but the treatment of each can be radically different, making specific diagnosis critical to the success of therapy and the safety of the patient.
Auto-immune dermatosis -- before treatment
Auto-immune dermatosis -- after 2 weeks of treatment
Auto-immune diseases tend to cause crusting and scaling, with or without loss of pigmentation. The face, nose, muzzle, eye regions and ears tend to be the most commonly affected by several of these diseases. The body, footpad margins, and mucous membranes can also be affected. Diseases that affect the mucous membranes are usually must more severe and require immediate diagnosis and treatment by a veterinary dermatologist.
The diagnosis of auto-immune disease requires biopsy sampling from affected areas. The choice of tissue for examination is very important in order to maximize the likelihood that a definitive diagnosis can be obtained. For this reason, the veterinary dermatologist should obtain and submit to the laboratory the patient skin samples.
The two most common auto-immune dermatitis diseases seen in the dog are pemphigus foliaceus and discoid lupus erythematosus. Pemphigus foliaceus (PF) is also seen in cats and horses, whereas discoid lupus erythematosus (DLE) is rarely seen in these two species.
DLE is primarily considered a cosmetic-disorder. Depigmentation of the nose leather, with swelling and loss of the normal cobblestone appearance, is most common. Crusting can develop, both on the nose and on the top of the muzzle, around the eyes, at the lip margins, and on the ears. However, this disease is confined to the face and does not extend onto the body. In severe cases, the crusting and cracking on the nose can become severe enough to result in tissue loss and significant bleeding.
DLE is sun-aggravated. Therefore, affected dogs should be kept out of the sun during the day, and have sunblock applied to exposed areas. Topical steroids and other immunomodulating drugs can be used to reduce symptoms. Oral tetracycline and niacinamide are also commonly used to reduce symptoms. Only rarely is systemic (oral) immunosuppression needed to heal lesions.
PF is a more aggressive disease. This auto-immune dermatosis can generalize to the body with large patches of crusts and erosions, resulting in scabs and oozing. Secondary infections easily follow, resulting in the patient feeling sick and painful. In both cats and dogs, the footpads and nail folds are particular areas of lesion development. Thick and adherent crusts, often with creamy pus-like debris can fill the nail folds. Crusts along the footpads may crack, causing pain.
The diagnosis of PF requires biopsy confirmation. Some cases can be tentatively diagnosed by examination of debris from the skin (cytology), but this is not entirely accurate. Because therapy involves a controlled but aggressive regimen of immunosuppressive medications, definitive diagnosis is critical before initiating therapy. The veterinary dermatologist may choose a combination of medications in order to control the immune system to sufficiently heal skin lesions, while leaving intact the ability of the immune system to prevent infections. Regular monitoring of treatment through examinations and laboratory samples will be required. It is very important that you follow the directions of the veterinary dermatologist precisely to permit the most favorable outcome. However, most dogs with this disease, when efficiently diagnosed and expertly treated, heal very well and live long and happy lives.