Clinical importance of changes in chronic pain intensity measured on an 11-point numerical pain rating scale

Abstract

Pain intensity is frequently measured on an 11-point pain intensity numerical rating scale (PI-NRS), where 0=no pain and 10=worst possible pain. However, it is difficult to interpret the clinical importance of changes from baseline on this scale (such as a 1- or 2-point change). To date, there are no data driven estimates for clinically important differences in pain intensity scales used for chronic pain studies. We have estimated a clinically important difference on this scale by relating it to global assessments of change in multiple studies of chronic pain. Data on 2724 subjects from 10 recently completed placebo-controlled clinical trials of pregabalin in diabetic neuropathy, postherpetic neuralgia, chronic low back pain, fibromyalgia, and osteoarthritis were used. The studies had similar designs and measurement instruments, including the PI-NRS, collected in a daily diary, and the standard seven-point patient global impression of change (PGIC), collected at the endpoint. The changes in the PI-NRS from baseline to the endpoint were compared to the PGIC for each subject. Categories of "much improved" and "very much improved" were used as determinants of a clinically important difference and the relationship to the PI-NRS was explored using graphs, box plots, and sensitivity/specificity analyses. A consistent relationship between the change in PI-NRS and the PGIC was demonstrated regardless of study, disease type, age, sex, study result, or treatment group. On average, a reduction of approximately two points or a reduction of approximately 30% in the PI-NRS represented a clinically important difference. The relationship between percent change and the PGIC was also consistent regardless of baseline pain, while higher baseline scores required larger raw changes to represent a clinically important difference. The application of these results to future studies may provide a standard definition of clinically important improvement in clinical trials of chronic pain therapies. Use of a standard outcome across chronic pain studies would greatly enhance the comparability, validity, and clinical applicability of these studies.

Transmucosal fentanyl vs intravenous morphine in doses proportional to basal opioid regimen for episodic-breakthrough pain

“…However, the minimal end point to efficacy has been found to be a decrease in pain intensity of at least 433%, 15 min after the study medications. This level of change in pain intensity has been best associated with clinically important differences by patients (Farrar et al, 2001). As expected, OTFC has been found to be more effective and rapid than oral morphine for treating breakthrough pain, producing a 433% change in about 42% of patients within 15 min after administration (about 32%) (Coluzzi et al, 2001).…”

Outcome of transcutaneous electrical nerve stimulation in chronic pain: short-term results of a double-blind, randomised, placebo-controlled trial

“…However it should be noted that VAS scores for pain intensity were measured once a day at a fixed time, reflecting the pain intensity at that particular moment, whereas patients' opinions about treatment result should include all improvements experienced by the patient during the whole treatment period. Interestingly, for patients satisfied with treatment results and willing to continue treatment, the mean pain reduction was 28.5%, a clinically important difference [25], whereas for patients not willing to continue treatment there was no improvement in pain intensity during the treatment period as compared to the baseline period. Regarding the accuracy of pain integration into this assessment, it is interesting to note that Coghill et al [26] found that individuals with similar activation patterns of the somatosensory, the anterior cingulate and prefrontal cortex provided similar subjective reports of pain magnitude.…”

Capsaicin 8% patch versus oral pregabalin in patients with peripheral neuropathic pain

“…Patients had PNP due to post‐herpetic neuralgia (PHN) (pain persisting for at least 6 months since shingles vesicle crusting), post‐traumatic nerve injury (PNI) (minimum of 3 months) or non‐diabetic painful peripheral polyneuropathy (minimum of 3 months), and had an average numeric pain rating scale (NPRS) (Farrar et al., 2001) score ≥4 over a period of at least 4 consecutive days. Patients had to be naïve to treatment with the capsaicin 8% patch and either naïve to treatment with pregabalin and gabapentin, or, in the opinion of the investigator, had not received adequate treatment with pregabalin or gabapentin (Dworkin et al., 2005).…”