Pain Intensity Difference Versus Pain Relief

Pain intensity scales may be categorical (e.g. none, mild, moderate, or severe), numerical rating (e.g. 11-point integer, 0-10), or numerical derived from a VAS. Pain relief scales are usually categorical (e.g. none, slight, moderate, good, or complete). Categorical data can often be converted directly to integers and analyzed as numerical data,81 differences are calculated by subtraction. Pain relief (PAR) may be more meaningful to patients; however, they need to refer back to the initial pain and, particularly with chronic pain, this may increasingly be influenced by subsequent events.62

Large differences in pain intensity always imply significant change, whereas complete pain relief may be of less significance if the initial pain was only "mild."

When a series of measurements is made, the sum of the differences in pain intensity (SPID) or the area under the pain relief curve may be calculated as outcome data. As well as pain, patients often cite decreased medication use, increased function, and improved sleep, as worthy end points of therapy.82


There now seems to be reasonable consensus from a variety of sources that a change in pain intensity of 30-60 percent, or two to four points on an 11-point scale, represents a clinically useful reduction in chronic pain.50' 83'84'85'86 Percentage pain reduction correlates better with patient global impression of change than does pain intensity difference, particularly when the initial pain report is high. Patients may view an 80 percent reduction in both pain and disability as desirable, but will consider 25 and 35 percent, respectively, to be worthwhile.87 Levels of depression and disability appear to modify expectations of outcome of treatment.88 The minimum clinically important change (MCIC) has been reported for back pain and associated disability; smaller improvements are more valuable in chronic pain states than in acute ones.89 Meanwhile, satisfaction with care may be rated as more important than satisfaction with improvement in pain


Outcome success may be specifically defined for individual conditions using a number of measures grouped together, for example the ACR-20 (American College of Rheumatology) responder index for rheumatoid arthri-tis,91 which includes pain and tenderness within a validated battery of measures to assess overall whether the treatment is effective. Similarly, a composite score has been defined for low back pain that attempts to amalgamate a number of measures into one index.92

A target end point may be used to direct therapy in clinical practice (e.g. 4 out of 10 on an 11-point VAS scale using i.t. hydromorphone for chronic benign pain93).

In summarizing group data, the proportion or percentage of patients achieving a specified level of analgesia (usually 30 or 50 percent) is used in preference to an averaged reduction in pain scores because it is more useful to know that 25 percent of patients in a study achieved 50 percent pain relief (definitely a helpful level of analgesia) than that there was a 20 percent reduction in pain scores across the whole study population (unlikely to be considered helpful).

Back Pain Relief

Back Pain Relief

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