OMERACT Endorsement of Measures of Outcome for Studies of Acute Gout

Breakout discussions

In relation to pain assessment, data had been presented from several trials that had applied a 5-point Likert scale, visual analog scale (VAS), and/or numeric rating scale to assess pain. Participants in the breakout group commented that the Likert pain scale has the advantages of convenience (particularly with electronic reporting diaries) compared to the VAS pain scale; VAS allows for more granular measurement, and trialists may choose either or both, because both appear to function very well in acute gout trials. Comments were also made for the future research agenda to consider the slope of pain improvement (that is, the rate of change in pain), the minimally acceptable state, time to pain resolution and achieving acceptable state, pain at rest versus pain on motion, measurement of pain behavior and pain impact, and to measure both change in pain as well as the achieved final state.

Comments were made specifically to acknowledge that pain and other patient-reported outcomes as well as measures of inflammation (joint swelling and tenderness) change so rapidly with effective treatment options for acute gout that reliability has less relevance for the psychometric assessment of any acute gout measure. This can be observed in Figure 1, which shows pain scores from a reported study of untreated acute gout over 7 days¹² superimposed upon data from an interventional study of etoricoxib and indomethacin for acute gout over 8 days¹³. It can be seen that even in untreated gout, pain improves over a matter of days. Most measures validated for acute gout domains have large effect sizes and discriminated well between groups and changes within a group, implying that these measures must be capable of demonstrating change beyond measurement error (even if the measurement error has not been formally quantified).

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Figure 1.

Pain improves quickly in acute gout (with or without treatment). The plot shows the mean (± SD) of pain scores (5-point Likert scale) from an interventional trial in acute gout (Merck, n = 339)¹⁶ and a cohort study of untreated acute gout (Bellamy, n = 11)^12,13.

Data from trials that used a physician-assessed 4-point Likert scale for joint swelling and tenderness were presented. Issues with regards to joint swelling and tenderness were also discussed in detail. Participants asked for clarification of whether these measures as reported were physician-assessed or patient-reported, and it was clarified that these were all physician-assessed. A suggestion was made to assess patient-reported joint swelling as another measure of this domain and perhaps this will need more validation data. Another suggestion was whether a sentinel joint should be monitored rather than multiple joints and how to assess swelling beyond a joint, when it affects the entire foot or leg.

We had presented data from acute gout trials that used a 5-point Likert scale patient global measure of change in response to treatment. The breakout groups debated the advantages and disadvantages of patient global disease measure (e.g., on a 0–10 or 0–100 scale with “no disease activity” and “severe/very severe disease activity” as anchors; or a Likert scale such as none, mild, moderate, severe, very severe) and patient global assessment of change (e.g., Likert scale), and suggested that both rather than 1 be measured in clinical trials. The groups noted that in gout trials, only Likert scales for global assessment of change were used, but similar to other rheumatic diseases, future trials need to include additional measures as discussed above. Participants also noted that patient global response to treatment scale was biased toward improvement, although they also recognized that improvement is almost the rule in the natural history of acute gout. They also suggested some other interesting versions of measures of return to pre-acute gout flare as considerations for global scales.

The current assessment of activity limitations in acute gout was generally viewed as unsatisfactory. The Health Assessment Questionnaire (HAQ) is specifically framed to assess the activity limitations over the previous week and contains many items related to upper extremity limitations. The breakout groups commented that because gout is a lower extremity predominant-arthritis with acute gout flares affecting the lower extremity, it was possible that either HAQ needed to be modified for lower extremity functional limitations, or another instrument more focused on lower extremity activity limitations should be used. Further, it was observed that acute gout evolves quickly and that an activity limitation measure should have the time frame of a day rather than a week for respondents to consider. Another issue raised was whether HAQ was a better instrument for measuring chronic as opposed to acute joint disease.

Plenary voting

The results of the voting are shown in Table 1. Overall, there was endorsement for the 5-point Likert scale and VAS (0 to 100 mm) to measure pain in acute gout; the 4-point Likert scale for joint swelling and joint tenderness; and the 5-point Likert scale for patient global assessment of response to treatment. A measure for the activity limitations domain was not endorsed.