Polyarthropathies are a diagnostic challenge in practice. Once it has been determined that an animal is suffering from inflammatory
joint disease, it is necessary to determine whether the disease is caused by infectious agents or is a result of an idiopathic
immune mediated disease. Often the underlying cause of immune mediated arthritis remains undetermined. If an infection is
present it isn't necessary for the causative organism to be present in the joint itself. However, antigen antibody immune
complex formation can occur with deposition in the joint. This then induces inflammation. When dealing with a case of polyarthritis,
every effort to eliminate infectious disease as the underlying etiology should be made since the treatment of inflammatory
arthropathies involves the use of immunosuppressive drugs. This could be disastrous if an infectious disease was present.
Diagnostic workup
A good history is a valuable source of important information. The possibility of tick contact (vector for disease) as well
as the recent administration of vaccinations the use of medications has to be determined. Vaccination and drug administration
have been associated with the development of inflammatory arthropathies, though infrequently. Heartworm status also needs
to be determined, since this is a systemic infestation that results in a strong immune mediated response in some animals.
As with all diseases, a good physical examination is vital. Palpation and manipulation of all joints should be performed to
determine which are affected. Polyarthropathies tend to more commonly involve the small joints such as the carpal and tarsal
joints. When palpating the joints, special attention should be paid for the presence of swelling, warmth or pitting edema.
In addition, every attempt should be made to localize potential sources of chronic infection or inflammation (i.e. prostate,
uterus, abscesses). The heart and lungs need to be carefully ausculted. Chronic lung infections or endocarditis are a potential
source of infection or antigen antibody complexes. The spinal column should be carefully palpated for the presence of pain
that might be suggestive of discospondylitis. It recently has also been demonstrated that many dogs with polyarthropathies
have concurrent meningitis which could also contribute to spinal pain. An ocular exam is also to be recommended, granuloma
formation can be seen with fungal disease (especially blastomycosis) or uveitis can be a part of a generalized immune-mediated
process.
Laboratory diagnosis
Since systemic disease can be the underlying stimulus for the development of a non-erosive polyarthropathy, a CBC, chemistry
screen and urinalysis are indicated. Toxic changes in the neutrophils might be indicative of infection. Anemias or thrombocytopenias
might be associated with the presence of immune mediated disease. A chemistry screen might reveal potential dysfunction in
other organs. Since many polyarthropathies are immune mediated, the presence of proteinuria with a benign sediment could be
significant and be indicative of the presence of concurrent glomerulonephritis. If proteinuria is present, this can be quantified
with a urine protein to urine creatinine ratio. In addition, urinary tract infection might be found. In certain cases blood
or urine culture may also be indicated.
The most important diagnostic test is arthrocentesis. Arthrocentesis allows the taking of a sample for both cytological and
microbiological evaluation. Joints that are easy to tap include the carpus and tarsus, elbow and stifle. Synovial fluid analysis
should be consistent with inflammatory joint disease before initiating therapy. This means that nucleated cell count should
be elevated, generally with greater than 5,000 nucleated cells per milliliter. Usually there is also a shift from a strictly
mononuclear population to a more neutrophilic cell population. Other signs of inflammatory joint disease include decreased
viscosity and increased turbidity. Wright stain or with Gram stain can be used to identify infectious organisms. If indicated,
aerobic, anaerobic and Mycoplasma culture should be obtained. Occasionally, synovial membrane biopsies can be taken if the
diagnosis is uncertain, though this is rarely necessary. Synovial membrane can be a good sample for culture and sensitivity
examination as well as histopathologic examination, it does however involve an arthrotomy.
Radiography can also be of value, though usually quite limited. Generally, early changes with most joint diseases will be
nonspecific if present. Chronic and long-term cases of bacterial arthritis may eventually cause changes consistent with erosive
arthritis. These signs consist of destruction of articular cartilage and subchondral bone with an irregular joint space, bone
erosions, periosteal new bone, osteosclerosis and osteophyte production.
Serologic testing may be indicated if appropriate physical examination or historical information are present. These include
titers for rickettsial and fungal organisms. Heartworm status of the dog should also be established since heartworm infection
can lead to chronic immune stimulation. In cats, testing for feline leukemia virus and FIV is of great interest.
