Patient reported outcome measures of pain intensity: Do they tell us what we need to know?

Abstract

Objective: To determine the relationship between chronic pain patients' responses to self-report measures of pain intensity, and self-reported strategies when completing such measures.

Participants: Ambulatory outpatients suffering from one of the following chronic pain conditions: painful HIV neuropathy, painful diabetic neuropathy, chronic Low-Back Pain.

Method: As part of a previously reported study using qualitative methods, participants completed standard pain intensity questionnaires as well as a measure of pain related disturbances in activities of daily living. In the previous study, participants' responses during a focus group were then used to identify their strategies and beliefs about their approach to completing the questionnaires. Among the beliefs were: (1) difficulties averaging pain over different time periods (i.e., "what was your average pain during the last 24h" versus "what was your average pain during the last 2 weeks"); (2) difficulty in comparing pain from different etiologies; (3) difficulties in reporting sensations of pain in a manner unaffected by issues and situations secondary to the pain experience, such as difficulties in activities of daily living. In the present paper we use ANOVA (analysis of variance) and partial correlation to determine whether the qualitatively derived perceptions are reflected in the quantitative pain intensity scores.

Results: Participants' belief that it was difficult to "average" pain intensity over different time periods was supported. The data do not support their belief that pain intensity scores are affected by other factors: their specific pain diagnosis, and the extent to which pain interfered with their activities of daily living.

Conclusions: (1) Patients tend to report different levels of pain intensity when asked to report their pain over different periods; (2) insofar as it can be said to exist, the relationship between measures of intensity and interference with activities of daily living is minimal; (3) participants tend to report similar levels of pain intensity, irrespective of etiology.

Implications: (1) Chronic pain patients' elicited beliefs and strategies concerning how they complete pain intensity questionnaires are sometimes, but not invariably, reflected in their responses to these measures. Thus, purely qualitative methodologies alone cannot provide completely reliable information and point to the need to use a "mixed methods" approach combining both qualitative and quantitative data; (2) the lack of association between pain intensity measures and interference with activities of daily living, as well as relative insensitivity to different etiologies underlines the problem in relying on pain intensity measures as the primary means of evaluating the success of a treatment, either for pain management or in clinical research.

Keywords: Chronic pain; Clinical trials; Outcome measures; Patient self-report.