History and clinical picture | Investigations |
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A | All patients with joint inflammation | - ESR, CRP, basic blood count with platelets, chemical urinalysis
- Anti-CCP antibodies if rheumatoid arthritis is suspected
- Synovial fluid analysis whenever fluid can be extracted (cells, crystals, bacterial culture and, if necessary, Gram staining)
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B | Monoarthritis (gout, pseudogout, bacterial arthritis, reactive arthritis); a patient with gout: typically uses beer or diuretics, arthritis in the first metatarsophalangeal joint | - Joint aspiration (cells, crystals, bacterial culture and, if necessary, Gram staining), plasma urate (the concentration may be low during an acute attack of gout)
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C | Prolonged joint inflammation / joint inflammation mainly affecting small joints (rheumatoid arthritis?) | - RF and anti-CCP antibodies
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D | Acute joint inflammation in a young adult and a positive history for preceding diarrhoea, ocular inflammation, sexual contact, urinary problems, purulent discharge from the urethra, other signs of infection, e.g. pharyngitis (infectious arthritis, reactive arthritis?) | - Stool sample, anti-Yersinia, anti-Salmonella and anti-Campylobacter antibodies if a positive history for gastrointestinal symptoms.
- A nucleic acid amplification test for Chlamydia from urine (or from a swab obtained from the urethra/cervical canal) and, if necessary, gonococcal culture.
- Anti-Chlamydia antibodies (the titre may stay high for a long period after the infection; the nucleic acid amplification test is preferred because of its superior sensitivity and specificity)
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E | A possible tick bite occurring in an area endemic for Lyme disease, or erythema migrans | - Anti-Borrelia burgdorferi (Lyme disease) antibodies (a negative result in early disease does not exclude Lyme disease)
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| Pox-like exanthema | - Rubella? Alphavirus antibodies if the patient has pruritic rash in the late summer or autumn. Parvovirus?
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F | Preceding febrile pharyngitis (rheumatic fever?) | - AST (antistreptolysin titre), streptococcal culture from the pharynx, ECG
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| A heart murmur, migratory polyarthritis, prolonged PR interval/signs of pericarditis (rheumatic fever?) | - AST (analysed if rheumatic fever is suspected on clinical grounds, a negative result speaks against rheumatic fever)
- Echocardiogram, chest x-ray
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G | Solar dermatitis, Raynaud's phenomenon (SLE and other systemic rheumatoid conditions) | |
H | Abnormal blood picture, severe pain at night (leukaemia, other malignant disease?) | - Differential white cell count and platelets; x-rays often needed
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