First reported in 1971, systemic lupus erythematosus (SLE) is a rare autoimmune disorder which can affect any organ system in the cat. Antibodies are proteins produced by the immune system to counteract and protect the body from antigens such as invading viruses and bacteria. However, sometimes the body produces antibodies against itself (known as auto-antibodies), attacking various systems including the skin, joints, blood vessels, kidneys, heart, and lungs.
The aetiology of SLE is unknown, although it is thought to be a combination of several factors including genetics, pharmacological agents, environmental, viral infection and exposure to UV light. Siamese, Persians, and their related breeds appear to be at greater risk of developing the disease. There is no age or sex predilection in cats.
The mechanism for damage is a type III hypersensitivity. Antigen-antibody complexes (or immune complexes) are formed when antibodies bind to antigens. These antigen-antibody complexes are deposited in the tissues which activate a number of immune responses which initiates an inflammatory response. This, in turn, stimulates neutrophils, phagocytes, and monocytes to the site. Phagocytes release toxic by-products which cause tissue damage.
What are the symptoms of SLE in cats?
Known as the 'great imitator' due to many symptoms mimicking other disorders to affect cats. Many body systems can be affected including the kidneys, skin, and joints. As such, clinical signs can be widely variable depending on the system affected.
Symptoms can be acute (sudden onset) or chronic, where the cat experiences symptoms on and off. The re-appearance of symptoms is known as a flare-up and remission is when symptoms abate.
- Joint pain and swelling associated with polyarthritis.
- Shifting leg lameness.
- Decreased mobility.
- Muscle weakness.
Renal (glomerulonephritis/kidney disease)
- Enlarged kidneys
- Ascites (fluid in the abdomen)
- Increased thirst
- Increased urination
- Weight loss
- Multifocal alopecia with crusty skin lesions, particularly on the head, face, ears, and rear legs
- Oral ulcers
- Nasal ulcers
- Paronychia (inflammation of the skin around the claws
Hematologic (hemolytic anemia)
- Pale or yellow mucous membranes
- Increased heart rate
- Blood in urine
- Blood in stool
- Red spots in the eyes and/or gums
- Behavioural changes
- Fever with no apparent cause
- Swollen lymph nodes
- Weight changes
How is SLE in cats diagnosed?
The criteria for diagnosing SLE in cats has been modified from the one created by the American Rheumatism Association (ARA) in which in human patients must meet four of eleven criteria in order for a diagnosis of SLE to be made including: rash, photosensitivity, oral ulcers, non-erosive arthritis, pleuritis/pericarditis, renal disorder, neurologic disorder, hematologic disorder, immunologic disorder and positive antinuclear antibody.
Your veterinarian will perform a complete physical examination of your cat and obtain a medical history from you. He will perform routine tests such as:
- Biochemical profile - Elevated BUN, hypoalbuminemia.
- Coombs test - This test is used to detect the presence of antibodies which bind to the surface of red blood cells in cats with hemolytic anemia.
- Complete blood count - May reveal anemia, low platelets, low white blood cell count, low lymphocytes, spherocytosis (round shaped red blood cells).
- Urinalysis - Proteinuria, elevated BUN.
- Antinuclear antibody test (ANA) - This test measures antibodies to self-tissues.
- Biopsy of a skin lesion.
- Kidney biopsy if glomerulonephritis is suspected.
- Xrays of the joints to check for arthritis.
- Synovial fluid (fluid from the joints) analysis.
- If the kidneys are involved, your veterinarian may want to check your cat's blood pressure as hypertension may be present.
How is SLE treated?
There is no cure for SLE, treatment is aimed at suppressing the cat's immune system. Your cat may be hospitalised initially until the condition is brought under control.
- Nonsteroidal anti-inflammatory drugs (NSAIDs) can be used to reduce inflammation and reduce fever.
- Corticosteroids such as Prednisone to reduce inflammation. Once the condition is under control, dosage may be tapered down to a lower dose.
Note: NSAIDs and corticosteroids should not be given concurrently due to severe side effects including gastroduodenal ulceration and renal papillary necrosis.
- Antibiotics to treat secondary infection.
- Limiting exposure to sunlight.
- Splenectomy (removal of the spleen) may be required in severe cases of thrombocytopenia.
- Supportive care including cage rest, especially during a flare-up, dietary management of kidney disease such as a low protein diet, medications to treat high blood pressure.
The prognosis for cats with SLE depends on the organs involved and how well your cat responds to treatment. But it is usually guarded, especially if the internal organs are affected. The earlier the diagnosis the better the outcome.