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Chronic pain - outcome recommendations


RH Dworkin et al. Interpreting the Clinical Importance of Treatment Outcomes in Chronic Pain Clinical Trials: IMMPACT Recommendations. Journal of Pain 2008 9: 105-121.

The Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials (IMMPACT) was a consensus conference to provide recommendations for interpreting clinical importance of treatment outcomes in clinical trials of the efficacy and effectiveness of chronic pain treatments. Its recommendations are shown in Table 1, for pain intensity changes, global ratings, physical and emotional functioning, and mood.

It suggests levels of response that could be interpreted clinically as minimal, moderate, or substantial improvements, as well as clinically important changes.

Table 1: Main IMMPACT outcome recommendations

Outcome domain and measure
Type of improvement
Pain intensity

0-10 numerical rating scale

Minimally important
10-20% decrease
  Moderately important
at least 30% decrease
at least 50% decrease
Global rating of improvement

Patient global impression of change (PGIC)

Minimally important
Minimally improved
  Moderately important
Moderately improved
Very much improved
Physical functioning
Multidimensional pain inventory interference scale Clinically important
at least 0.6 point decrease
Brief pain inventory scale Minimally important
1 point decrease
Emotional functioning

Beck depression inventory

Clinically important
at least 5 point decrease
Profile of mood states

Total mood disturbance

Clinically important
at least 10-20 point decrease

Specific subscales

Clinically important
at least 2-12 point change



This is a really important insight, because it changes the emphasis in clinical trials from what happens to the population average to what happens to the individual. It implies that trials should use these criteria to determine what's important, measure it, and then tell us what proportion of patients achieved the outcome. Figure 1 is a simple aide-memoir for pain trials.

Figure 1: Main pain response outcomes