Key distinguishing features of the most common diagnoses
|OA||CP/Anterior Knee Pain||Traumatic Synovitis||Gout||Traumatic Haemarthrosis|
|History of Acute Trauma||Possible||No||Yes||Possible||Yes|
|Several Joints Painful||Possible||No||No||Possible||No|
|Hot, Red Joint||No||No||No||Yes||Possible|
Possible:FBC, ESR/CRP, uric acid, X-ray, joint aspiration (in monoarthritis of large joint).
Small Print:Rheumatoid factor/anti-CCP antibodies, clotting studies/factor VIII assay, arthroscopy.
- FBC/ESR/CRP: WCC and ESR/CRP raised in infection, systemic inflammatory conditions; Hb may be reduced in the latter.
- Uric acid: Once attack has subsided, useful to add weight to clinical diagnosis of gout (especially if considering treatment with allopurinol).
- Rheumatoid factor may be useful if symptoms suggest possible RA (consider anti-CCP antibodies if rheumatoid factor is negative).
- X-ray: Essential if fracture suspected. May also reveal OA, avascular necrosis, malignancy and help to distinguish between RA and psoriatic arthritis.
- Sterile aspiration of joint fluid: To look for pus (septic arthritis), blood (haemarthrosis) and crystals (gout/pseudogout).
- Clotting studies/factor VIII assay: If haemophilia a possibility.
- Arthroscopy: May be required urgently in secondary care if trauma has resulted in a haemarthrosis.
- Autoimmune blood tests can be misleading in possible arthritis. The diagnosis should be clinical; blood testing simply adds weight and prognostic information to the clinical assessment. Positive tests can be found in normal patients – beware of inappropriately labelling an insignificant problem as a significant arthritis on the basis of a blood test.
- Gout is very painful, will limit movement and may cause a slight fever. Septic arthritis gives a similar picture but with marked restriction of movement and, usually, a high fever. If in doubt, arrange urgent assessment.
- In obscure cases, question and examine the patient carefully. For example, in reactive arthritis, symptoms of urethritis or conjunctivitis may have been minimal or forgotten; in psoriatic arthritis, there may only be insignificant skin lesions.
- If one joint is red, very hot, intensely painful with marked limitation of movement and systemic illness, septic arthritis must be excluded – admit.
- Haemarthrosis usually develops rapidly after trauma and indicates significant damage requiring immediate referral; effusion due to synovitis usually takes a day or longer to accumulate and is less urgent.
- Septic arthritis is notoriously easy to miss in a patient with coexisting RA. The systemic signs may be absent and the diagnosis may mistakenly be viewed as a flare-up of rheumatoid arthritis.
- Consider reactive arthritis in a young adult male with a monoarthritis of the knee not caused by trauma.