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Clinical investigation 

Clinical investigation

Chapter:
Clinical investigation
Author(s):

Michael Doherty

and Peter C. Lanyon

DOI:
10.1093/med/9780199204854.003.1903
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date: 25 March 2017

Laboratory and imaging markers are an adjunct to competent clinical assessment and should not be used as a substitute. Tests should only be ordered if the results will alter diagnosis, prognosis, or clinical management.

Synovial fluid examination—this is the key investigation to confirm the diagnosis of either acute crystal or septic arthritis. Fluid can usually be obtained by direct aspiration from any peripheral joint, or alternatively under ultrasound guidance. The identification of crystals requires compensated polarized light microscopy.

Plain radiographs—these remain the single most useful imaging technique, enabling the detection of soft-tissue swelling, changes in bone density, and cartilage and bone erosion or remodelling, which in conjunction with the pattern of joint sites involved can aid confirmation of diagnosis and assessment of disease extent. The cardinal radiological features of rheumatoid arthritis are osteopenia and cartilage/bone erosion: the features of osteoarthritis are preserved bone density, joint-space narrowing, osteophyte formation, and bone cysts.

Other imaging techniques—(1) MRI provides additional benefit with plain radiographs in the assessment of the anatomy and biochemistry of soft tissues as well as bone; (2) ultrasound is emerging as an effective bedside technique for detecting joint effusions (particularly at clinically occult sites) and to assess joint erosions and neovascularity.

Blood tests—(1) inflammatory markers: C-reactive protein is the single most useful measure of the acute phase response, having greater reproducibility and greater sensitivity to change than the ESR; (2) specific antibodies: antibodies to cyclic citrullinated peptides are a novel marker associated with rheumatoid arthritis, with similar sensitivity to rheumatoid factor but higher specificity for distinguishing between rheumatoid arthritis and other rheumatic diseases; antibodies detected against nuclear components (ANAs) have high sensitivity for connective-tissue diseases (e.g. systemic lupus erythematosus) but low specificity, and hence a positive result does not confirm the diagnosis unless appropriate clinical features are present. Compared with ANA, antibodies to extractable nuclear antigens have higher specificity and associate with patterns of system involvement within the same disease.

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