Systemic lupus erythematosus

A multisystemic, chronic autoimmune disease in which the body creates specific and non-specific antibodies against the nuclei of cells in different organs and tissues. Autoantibody levels increase due to a decrease in the number of T lymphocytes and an increase in B lymphocytes. Circulating immune complexes are deposited in the synovial membrane of the joints, the renal glomeruli, and the basement membrane of the skin, as well as in erythrocytes and platelets, which triggers type I, II and III hypersensitivity reactions. Subacute periods alternate with “resting” phases over the course of the disease.

Although the aetiology is unclear, genetic factors, viral and bacterial infections, and alterations in immunomodulatory mechanisms are known to play an important role in triggering the onset of lupus. Some dog breeds are predisposed to developing the disease: Collies, German Shepherds, Beagles, Poodles and Irish Setters. The most commonly affected feline breeds appear to be Persians and Siamese. The disease occurs more frequently in dogs than in cats and has a predilection for males over females.

Symptoms

Given its multisystemic nature, lupus can manifest in a variety of ways, and can even be confused with other chronic diseases. Animals will present one of four basic symptoms:

• Pyrexia (100%).
• Non-erosive polyarthritis (90.6%).
  Lameness in extremities due to polyarthritis.
• Kidney failure (65.3%).
  Oedema and ascites due to hypoproteinaemia when associated with glomerulonephritis.
• Skin disorders (60%).
  Photosensitization and involvement of areas with greater exposure to sunlight. The lips, nose, ears (if erect) and areas with less hair such as the axilla, groin and stomach are the most affected parts of the body. Crusting and ulceration develop mainly on the nose. These can eventually erode the nasal cartilage, cause depigmentation of the mucocutaneous junctions and pads, plantar hyperkeratosis, seborrhoea and erythema, as well as secondary pyoderma.

Other symptoms include keratoconjunctivitis sicca, petechiae and ecchymosis due to thrombocytopenia and/or vasculitis, jaundice due to autoimmune haemolysis, pleural effusion, lymphadenopathy, splenomegaly, polyclonal gammopathy, CNS alterations such as generalised or focal seizures, and muscular pathologies such as polymyositis or myasthenia gravis. Lupus can also be associated with lymphocytic thyroiditis and its corresponding symptoms.

The cutaneous form of lupus, without systemic involvement or laboratory alterations, is called Discoid Lupus Erythematosus (very rare in cats). One of the manifestations of systemic lupus erythematosus (SLE) is Bullous SLE, which involves systemic alterations and the formation of subepidermal vesicles.

It is important to perform an accurate differential diagnosis to rule out other pathologies, such as Leishmaniasis and Pemphigus, Ehrlichiosis, multiple myeloma, and subacute bacterial endocarditis, among others.
Symptoms in cats may differ somewhat from canine symptoms, and include abnormal behaviour, facial tremors, and weight loss in addition to the characteristic symptoms of lupus. Only one third of affected animal present lameness.

Interpretation of laboratory tests

General tests:

• Complete blood count: Haemolytic anaemia (Coomb's positive in 17% of cases), leukopenia (neutrophilic leucocytosis may sometimes be observed) and occasionally thrombocytopaenia.
• Serum protein. Hypoalbuminaemia, hyperglobulinaemia.
• Blood biochemistry: Elevated BIL, ALP, GOT, GPT and BUN.
• Urine: Usually proteinuria with or without the presence of bilirubinuria.

Specific tests

• Lupus erythematosus (LE) cell test:
  LE cells are leukocytes, generally neutrophils, that have phagocytized the nucleus of another leukocyte opsonized by antinuclear antibodies and the complement. The test is positive in 80% of cases, and some authors consider it to be reasonably specific.
• Antinuclear antibody (ANA) test:
  A highly sensitive test (positive in 97%-100% of dogs with SLE), but other autoimmune and/or neoplastic diseases can also give positive results. Negative titres rule out a diagnosis of SLE with a probability of over 99%. High positive titres, together with symptoms consistent with SLE, are considered highly indicative of SLE.
  It is important to bear in mind that healthy dogs (16%-20%) and cats may present positive ANA titres.
  The animal should be tested again after 2-3 months to observe the evolution of the disease and rule out the possibility of a false positive result due to medication or inflammatory processes.
  ANA titres decrease as the disease comes under control, but symptomatic improvement occurs earlier.
• Biopsy of non-ulcerated areas:
  Skin, kidneys. Samples are taken from the border of the lesion Complement and Ig deposits are determined using indirect immunofluorescence.

Complementary tests, such as bone marrow aspiration, can be performed to confirm the diagnosis. The presence of LE cells can also be determined in the fluid obtained by thoracentesis.

Bibliography

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