What is systemic lupus erythematosus?
Systemic lupus erythematosus (SLE) is an immune-mediated disease, rare in cats, that causes the immune system to see the body’s own cells and related matter as antigens (foreign substances). The cat’s immune system mistakenly starts to attack parts of its own body instead of protecting it. The immune system makes antibodies that stick to targets in the body, forming clusters (antibody-antigen complexes). Because of the overwhelming numbers of these clusters, the body can’t clear them normally and they collect in certain tissues, where they trigger more inflammation and damage.
Because of the overwhelming numbers of these complexes, the body can’t clear them normally. They are deposited in certain tissues, where they trigger more inflammation and damage. Siamese, Himalayan, and Persian cats appear to be more likely than other breeds to develop SLE.
What are the clinical signs of SLE?
SLE can affect many body functions and systems, depending on the specific immune dysregulation that occurs. Approximately 60% of affected cats have skin lesions. These lesions may appear as reddening of the skin, crusted ulcers, or open sores caused by the immune system’s attack on the skin. Most often, these skin lesions are noted on the face, ears, and paws, but they can be generalized across the body.
Affected cats also show signs of systemic illness due to the effects of SLE on other body systems. Signs may appear suddenly or they may be slower to develop. In some cats, signs wax and wane over time. Signs of systemic illness include:
- Fever that does not respond to antibiotics
- Lameness
- Joint swelling and/or pain
- Stiff gait
- Decreased appetite
- Lethargy (decreased energy)
- Oral ulcerations
- Kidney disease
- Neurologic abnormalities
- Enlarged lymph nodes
- Liver and/or spleen
- Evidence of anemia (pale gums, weakness)
- Bleeding disorders
How is SLE diagnosed?
There is no single test to diagnose SLE, making it a challenge for veterinarians to diagnose. Most veterinarians use the American College of Rheumatology’s “Eleven Criteria of Lupus” to establish a diagnosis of SLE. In human patients, four of these 11 criteria must be present to come to a diagnosis. In veterinary patients, just three of these criteria can suggest a likelihood of the disease.
The Eleven Criteria of Lupus:
- Butterfly-shaped facial rash
- Discoid rash (raised red patches on the skin)
- Photosensitivity (skin rash in response to sunlight)
- Mouth or nose ulcers
- Inflammation in two or more joints
- Inflammation of the lining around the heart or lungs
- Neurologic disorders, including seizures
- Kidney function abnormalities
- Blood disorders such as anemia, low white blood cell count, or low platelet count
- Antibodies against certain components of the blood and cells
- Antinuclear antibodies (ANA)
Skin biopsies are frequently performed in the early evaluation of SLE. Your veterinarian will use sedation and a local anesthetic to obtain a small skin sample from an affected area of your cat’s body. A pathologist may notice certain skin changes associated with SLE, which may help with the diagnosis. The pathologist may also use specialized techniques to check for the presence of antibody deposits in the skin.
Your veterinarian will also perform bloodwork to assess your cat’s cell counts and organ function. Cats with SLE often have anemia (low red blood cell count), as well as decreased numbers of platelets and white blood cells. An antinuclear antibody (ANA) test may also be performed if your veterinarian suspects SLE. This test checks for antibodies to the body’s own cells.
What causes SLE?
A single definitive cause of SLE has not been identified, but genetic, physiologic, and environmental factors probably play a part in its development. Several factors are believed to trigger SLE, including stress, infections, certain medications, and exposure to UV light. These triggers are believed to activate the genes that make a cat susceptible to SLE.
How is SLE treated?
Treatment of SLE relies on suppressing the overactive immune system. Most frequently, this immunosuppression is performed with corticosteroid drugs, such as prednisolone or dexamethasone. In more severe cases, additional immunosuppressive drugs such as cyclosporine (Atopica™), chlorambucil, cyclophosphamide, or mycophenolate mofetil (MMF) may be required.
Cats with SLE should be kept indoors, as exposure to sunlight will worsen the severity of the skin lesions. Due to the possibility of a genetic component of the disease, affected cats should not be bred.
What is the prognosis for SLE?
SLE is a devastating disease that can be difficult to treat. It is progressive and unpredictable. Cats with this diagnosis require long-term treatment to decrease the immune response. Suppressing the immune system has potentially serious side effects, making both the disease and its treatment hazardous.
SLE is a serious condition, and the prognosis is uncertain (guarded), even with treatment. Some cats survive with lifelong immunosuppressive treatments, which require lifelong, frequent monitoring. Others cannot achieve control of their symptoms even with appropriate medical therapy.
