• power Doppler sonography
• echo contrast agent
• rheumatoid arthritis
• synovial tissue

We read with interest the paper by Carotti et al that appeared in the October issue of the Annals of the Rheumatic Diseases.¹ The authors investigated the usefulness of contrast enhanced power Doppler ultrasonography (PDS) in determining the vascularisation rate of the synovial pannus of patients with rheumatoid arthritis (RA). After intravenous infusion of an echo contrast (Levovist, Schering, Germany) PDS was performed on the knee joints of 42 patients with RA, who had previously been classified as having active (n=15), moderately active (n=14), and inactive knee synovitis (n=13). The results were expressed as the area underlying time-intensity curves. Highest vascularisation scores were found in patients with active synovitis (216.2 (33.4), mean (SD)), whereas lower values were found in those with moderately active (186.8 (25.8)) and inactive synovitis (169.6 (20.6)). Significant difference (p<0.01) was found between the active and the inactive group only. Also, significant correlations were found between the vascularisation scores and some indices of the disease activity. The authors concluded that PDS may be a valuable method of distinguishing between inflammatory and non-inflammatory pannus of knee joints in RA and thus may have a clinical potential for both diagnostic and therapeutic purposes.

Unfortunately, Carotti et al did not provide any data on the sensitivity and specificity of the method used. Moreover, no figure showing distribution of the vascularisation scores in individual patients and/or confidence limits of the mean was available. This is a major problem and, in our opinion, the data presentation does not allow for any conclusions about how the PDS really performs in clinical settings. It should be emphasised that statistical significance alone is not sufficient as it could easily be achieved if there were some lower and some higher vascularisation scores in …