Systemic Autoimmune Disease in Cats

Commonly, the signs of systemic autoimmune disease are vague, such as lack of energy, weakness, skin ulcers, joint pain, and weight loss. A definitive cause is often not identified but a genetic tendency (such as with Persians and their crosses) or viral triggers are suspected in many cases. The long-term outlook is poor.

Systemic autoimmune disease (SAD), also known as Systemic Lupus Erythematosus (SLE), affects the cat’s immune system such that it attacks its own cells. The damage done and resulting symptoms depend on which tissue is targeted. For example, if red blood cells are attacked, the cat becomes weak due to anemia from lack of blood cells. 

Systemic autoimmune disease can potentially destroy any body tissue, depending on which cells are mislabeled for attack. Thus, the signs of disease vary depending on what part which tissue is damaged. This leads to vague symptoms that should alert the cat owner their pet is unwell and to seek professional veterinary advice. Common clues include one or more of the following: 

• Weakness and Lethargy: This can arise because of anemia or because the cat feels unwell.
• Skin lesions: A common site of problems is where the skin meets mucous membranes, such as the lips, eyes, and anus. The skin becomes inflamed, ulcerated, and scabby.
• Bleeding: One form of SLE attacks thrombocytes, whose job it is to clot blood.
• Lameness: Another form of SLE targets the joints, causing pain and a shifting lameness.
• Excessive thirst: This is most typical when the kidneys are targeted
• Waxing and waning illness: The cat may not be ill all the time but have ‘good’ and ‘bad’ days.
• Poor appetite and weight loss

This disease is caused by the immune system when it turns on itself and damages normal, healthy tissue. The body’s immune system produces antibodies (which fight infection and destroy diseased cells) in response to antigens (substances that trigger an immune reaction.) Normally the body ignores its own antigens, but when for some reason it misreads self-antigens as foreign, this results in destruction of its own tissue. Possible reasons why this happens include:

• A genetic tendency: Breeds such as the Siamese, Persian, and Persian crosses are over-represented amongst cats suffering from SAD
• Viral infections
• Hormonal factors

This said, the underlying trigger is rarely identified and usually remains a mystery. 

Unfortunately, diagnosis is not always straightforward, since the tests are associated with a high percentage of false negatives. This means, although the test result comes back negative, if the cat has highly suggestive symptoms then SAD cannot be ruled out and the vet may need to probe deeper still. 

After taking a history, the vet examines the cat and takes note of symptoms such as pale gums, joint pain, an enlarged spleen, or evidence of recent bleeding. This helps the vet to rule some conditions out, as well as decide which tests are most helpful. 

An appropriate first step is a general blood profile which looks at hematology (the cat’s red and white cells) plus biochemistry. This gives an overview of whether the cat is anemic or deficient in a particular cell line, and if there is organ damage. The vet uses this information to pinpoint further tests. Unfortunately, no one single test is 100% accurate or 100% reliable, so false negatives and false positives can confuse the picture. 

Further blood tests used include:

• Anti-Nuclear Antibody (ANA) test: False positives can occur with liver disease or in feline leukemia positive cats.
• Coombs test: False negatives can occur in mild SAD
• Examining a fresh blood smear under the microscope: Looking for specific types of red blood cell damage that indicate attack by the immune system

In addition, the vet may harvest samples from specific areas that are affected, such as a skin biopsy or joint fluid. 

Treatment is based on using drugs to switch off the inappropriate immune response and stop the body attacking itself. Surgical intervention is not appropriate or helpful. 

Corticosteroids

High doses of corticosteroids such as prednisolone are often used as the first option as they are highly effective and inexpensive. These drugs are usually given daily by mouth so that fine dose adjustments can be made. They should be given with or after food to reduce the risk of gastric ulceration

High doses are initially given for two to four weeks until a sustained improvement occurs. After that, the dose is decreased incrementally every two to four weeks. The aim is to stop treatment once the SAD has switched off. Unfortunately, relapses are common at some point in the future.  

Steroids are associated with side effects such as increased thirst and appetite in the short term, and the possible complication of inducing diabetes or Cushing’s disease in the long term. Regular monitoring of the blood is necessary to check the response to treatment; this may be weekly or bi-weekly at first.  

Other Immunosuppressive Drugs

Should the cat fail to respond to corticosteroid treatment, other immunosuppressive drugs such as azathioprine can be added into the protocol. Many cats respond to initial treatment for a period of time but relapses are common. 

For those cats on treatment, regular follow-up appointments and blood tests are essential. This allows dose adjustments (up or down) to be made, depending on how the pet is responding. A sick or weak cat may need hospitalization for the first few days of treatment, in order to receive a blood transfusion or supportive intravenous fluids. Once stable, or if the SAD is mild, treatment is undertaken at home with daily or alternate day doses of medication. 

The short-term outlook is favorable when the problem is diagnosed before it reaches a crisis point, but deterioration or relapse are common and associated with a high mortality rate. 

For those cats that respond to treatment, the owner must be vigilant for relapse and seek urgent veterinary attention should their cat become unwell.