The diagnostic value added by musculoskeletal ultrasound (MSUS) over standard clinical and laboratory parameters has proved difficult to quantify. The additive contribution to diagnostic classification of a pragmatic, 15 min MSUS protocol was appraised in a large, unselected cohort of early arthritis clinic attendees.
Detailed baseline characteristics were recorded. Semi-quantitative MSUS scoring of the most symptomatic wrist, second/third MCPs and PIPs and second/fifth MTPs was recorded, along with the sonographer's scan impression (definitely inflammatory, possibly inflammatory or non-inflammatory). MSUS findings were available to rheumatologist diagnosticians during subsequent consultations. Persistent inflammatory arthritis (PIA) was classified only where patients were started on ≥1 DMARD. Multivariate and receiver operating characteristic (ROC) curve analyses were used to identify independent discriminators of PIA, and the added value of MSUS parameters.
Eight hundred and thirty-one patients were enrolled, of whom 31.3% acquired a PIA diagnosis. Swollen joint count, CRP, age and ACPA status were non-redundant clinical/laboratory predictors of a PIA diagnosis by consulting rheumatologists, with good discriminatory utility (area under the ROC curve, AUROC, 0.88). While the additive contribution of summed parameters from the seven-joint MSUS protocol to this model was statistically significant (P = 0.004), it was numerically small (ΔAUROC 0.02). However, the additive contribution to diagnostic outcome of sonographer's scan impression over clinical parameters alone became substantial in the sub-cohort of ACPA-negative patients, increasing the AUROC by 9% from 0.81 to 0.90 (P < 0.0001).
The clinical utility of a 15-min MSUS screen for diagnosing PIA requiring DMARDs is most evident among ACPA-negative patients attending an early arthritis clinic.