Immune-mediated polyarthritis (IMPA) is a sterile inflammation of the synovium in two or more joints, driven mainly by deposition of immune complexes in the synovial membrane. It is a common disease of dogs, and fever is frequent: about two-thirds of dogs in one large series were febrile. Because dogs often show fever, lethargy and stiffness rather than obvious joint swelling, it is easy to miss unless joint fluid is sampled.
Key facts
Immune-mediated joint disease (immune-mediated polyarthritis) at a glance- Species and system: dogs (cats also get IMPA, but in cats polyarthritis is more often infectious); musculoskeletal, synovial joints.
- Cause: type III hypersensitivity: immune complexes lodge in the synovium, complement is activated and neutrophils flood the joint. Idiopathic, or reactive to infection, gut or liver disease, neoplasia, drugs or vaccines.
- Classic presentation: young to middle-aged dog with fever, lethargy, reduced appetite, a stiff or shifting-leg lameness and several warm, effused joints, especially carpi and tarsi.
- Key test: arthrocentesis of several joints showing increased cells with more than 10–12% non-degenerate neutrophils and no organisms, plus a negative culture.
- Classification: non-erosive (most cases; types I–IV) or erosive (rheumatoid-like; uncommon).
- Zoonotic/reportable: no, but it can be the joint form of tick-borne infections that matter for public health.
What's inside
13 sections in the full guide- Key facts
- How the NAVLE tests this
- Cause and pathophysiology
- Clinical signs
- Diagnosis
- Related syndromes
- Differential diagnoses
- Treatment and management
- Prevention, control and public health
- Prognosis
- Quick review
- Test yourself
- References
The full guide also has 6 tables, 2 figures, 3 self-test questions and 20 references, available to NAVLE members.
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