Objectives To determine whether non-steroidal anti-inflammatory drugs (NSAIDs) have a significant effect on ultrasonographic (US) grey scale (GS) and power Doppler (PD) assessment of synovitis in rheumatoid arthritis (RA).

Methods Patients with RA taking NSAIDs were randomised to either stopping (for a minimum of 5 drug half-lives) or continuing the drug. All patients had a clinical assessment and US examination of both hands and wrists before and after stopping/continuing the NSAID. Changes at follow-up were compared between groups using Mann–Whitney U tests.

Results A total of 58 patients with RA were recruited. All the clinical assessment parameters (including disease activity, pain, general state of health and physician global visual analogue score and tender and swollen joints count) showed an increase in the group who stopped their NSAID treatment. The total GS and PD score showed median (first to third quartiles) increase of 9.5 (5.75 to 19.0) and 4.0 (2.0 to 6.0) per patient, respectively, in the patients who stopped their NSAID in comparison with 1.0 (–1.0 to 2.25) and 0.0 (–2.0 to 3.0), respectively, in the patients who continued their NSAID (p<0.001). There was an increase in the number of joints scoring >0 for GS and PD in the patients who stopped the NSAID. The inter- and intrareader agreement was good to excellent for the US examination.

Conclusion NSAID usage may mask the GS and PD signal and result in lower scoring despite continuing disease activity. Consideration should be given to the NSAID effect in designing clinical studies which use US to assess response to therapeutic.