Lupus – especially systemic lupus erythematosus - is not particularly easy to diagnose. The veterinarian must consider and rule out a number of other disorders that can mimic the symptoms of lupus before a diagnosis can be confirmed.
Discoid lupus erythematosus (DLE) is less difficult to diagnose than its systemic counterpart. Usually, depigmentation of the skin on the nose, followed by the characteristic scaling, ulceration and crusting of facial skin, is diagnostic of DLE. Skin biopsies can be taken of non-ulcerated, depigmented facial areas for microscopic histopathologic examination.
Systemic lupus erythematosus (SLE) cannot be diagnosed based on any single test. The attending veterinarian must consider and exclude other possible causes of the dog’s symptoms, such as pemphigus erythematosus, pemphigus foliaceus, cancer, tick-borne disease, kidney disease, bacterial/fungal/viral infection, musculoskeletal disorders and heart disease, among others. The results of a urinalysis and routine blood tests can vary widely based on the organ or organ systems affected by SLE. A skin biopsy and an antinuclear antibody (ANA) test can be helpful to confirm the diagnosis in many cases. A lupus erythematosus (LE) test is available to support the diagnosis, although the test is cumbersome and rarely used. Arthrocentesis can be used to sample joint fluid. Radiographs (X-rays) of affected limbs may disclose a non-erosive form of arthritis, which differs from the erosive lesions seen in dogs with rheumatoid arthritis.
It is important to rule out infectious causes of a dog’s symptoms before treating it with immunosuppressive medications.