Periarticular osteoporosis: a useful feature in the diagnosis of early rheumatoid arthritis? Reliability and validity in a cross-sectional diagnostic study using dual-energy X-ray absorptiometry

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Objectives. To identify regions of interest (ROIs) relevant to periarticular osteoporosis in RA with low precision error and sufficient inter-rater reliability and to test diagnostic validity for RA.

Methods. Periarticular BMD was measured using dual-energy X-ray absorptiometry (DXA). Five ROIs were defined around MCP and/or PIP joints II–V, II–IV and mid-metacarpal to mid-phalangeal. They were evaluated for precision using the root mean square coefficient of variation (RMS-CV) and the intra-class correlation coefficient (ICC) for inter-reader reliability. To test validity, established RA patients (n = 25) and early arthritis patients (n = 25) were compared with healthy controls (n = 37) matched on sex, age and menopausal status using paired t-tests, ROC curves and scatterplots.

Results. The RMS-CV was 0.45–1.07%. The ICC was 0.99. Mean BMDs of the five ROIs ranged from 0.321 to 0.372 g/cm2 in established RA, from 0.321 to 0.382 g/cm2 in early arthritis and from 0.342 to 0.401 g/cm2 in healthy controls. Mean differences ranged from 0.012 to 0.032 g/cm2 for established RA and from 0.023 to 0.033 g/cm2 for early arthritis patients compared with matched controls, with P < 0.05 for ROIs 1–5 in early arthritis and the whole hand in established RA. ROC curves indicated low discriminative power, with an area under the curve (AUC) of 0.61–0.64, and scatterplots showed great overlap between BMD values of patients and controls.

Conclusions. Periarticular BMD measured with DXA seems not to be a useful diagnostic feature due to strong overlap of BMD values between healthy controls, established RA patients and early arthritis patients.

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