An ongoing question of concern facing practitioners treating patients for chronic pain conditions, as well as the patients themselves, is “How much pain relief is enough?” A recent large-scale study of treatment for knee or hip osteoarthritis assessed the amount of pain relief that patients judge as being of significant benefit.
Various patient-reported outcome measures have been developed to achieve more relevant assessments of treatment success in clinical trials and during everyday pain management. Two important measures, especially for assessing pain relief, are called the “patient acceptable symptom state” (PASS) and “minimal clinically important improvement” (MCII).
The PASS is defined as the symptom score beyond which patients with pain essentially consider themselves to be “feeling well.” It is reflected overall in an affirmative answer to the question, “Considering all the different ways in which your disease affects you, if you were to remain in this state for the next few months, would you consider this to be satisfactory?” Whereas, MCII depicts the smallest change in a patient’s symptom score, given that the patient has improved, which encompasses the concept of “feeling better.”
To assess these patient-reported outcomes in everyday clinical practice, researchers in France conducted a nationwide multicenter cohort study of patients over the age of 50 years with pain from knee or hip osteoarthritis (OA) measuring at least 3 on a 0-to10 numerical rating scale (NRS), and who had visited their general practitioners for analgesic treatment lasting ≥7 days [Perrot and Bertin 2013]. Overall, 2,414 evaluated patients — 50% men, 33.5% with hip OA, average age 67 years, mean duration of disease 5 years — had been treated by 1,116 participating general practitioners.
Prescribed analgesic pharmacotherapy was classified according to the 3 Levels/Steps of the World Health Organization Analgesic Ladder (see figure). Generally, treatments in both hip OA and knee OA groups were similar, with most patients (74%) requiring Level 2 analgesics, 44% receiving Level 1 analgesics, and 29% receiving other drugs. Furthermore, 28% were prescribed physiotherapy, and 14% of those with knee OA and 2.4% with hip OA were administered intra-articular injections. Many patients received multiple therapies, so the numbers add up to more than 100%.
Writing in the journal PAIN, the researchers report that, at baseline, mean NRS pain scores were roughly 5.1 at rest and 7.0 on movement in both groups. Most patients (≈90%) considered their pain after 7 days of treatment to have improved and mean NRS scores were reduced to 3.2 at rest and 4.4 during movement, for both hip OA and knee OA.
The NRS score representing a patient acceptable symptom state (PASS) — the point at which they were feeling “well” — was determined by the researchers to be 4.0 points at rest and 5.0 on movement. These PASS values were achieved in both groups by 79% and 75% of patients at rest and during movement, respectively, after the 7 days of treatment.
The NRS rating change required for minimal clinically important improvement (MCII) — feeling “better” — was determined to be a decrease of 1.0 point after 7 days of usual treatment, for knee or hip OA and both at rest and on movement. In this study, almost all participants (89%) reaching a patient acceptable treatment state, or PASS, also achieved an MCII at rest and during movement; so, the two were closely linked.
The researchers conclude that, in primary care settings, patients with lower-limb osteoarthritis may be considered to have achieved an acceptable symptomatic state of “feeling well” if they assign a score while resting of <4.0 to their pain on a 0-to-10 NRS (or <40 mm on a 0-100 Visual Analog Scale, or VAS) and a score during movement of <5.0 (or <50 mm on VAS) — both of which correspond to no worse than mild pain. Along with that, the cutoff for MCII (minimal clinically important improvement) of feeling “better” is a decrease in score by 1.0 point on NRS (-10 mm on VAS).
COMMENTARY: The question of “How much relief from chronic pain is enough?” has been discussed is previous UPDATES articles [eg, see here]. This present observational study was large in scale but of short duration, assessing improvements during merely one week of therapy that might have been rather intensive and involving multiple analgesic medications and other modalities. On average, patients had moderate pain at baseline — 5.1 at rest, 7.0 during motion (on NRS) — and were not taking analgesics or receiving other pain relieving therapies.
Therefore, patients may have been highly responsive to pain-relieving interventions, at least short-term. Outcomes after 7 days were statistically significant, with large pain-relief effect sizes of 1.03 at rest and 1.58 during motion (Cohen’s d calculated from study data). Pain was reduced to within the mild range — 3.2 and 4.4 at rest and motion, respectively — which the researchers determined was within parameters that patients would accept as “feeling well.”
Whether this actually would be the case among all patients and in all clinical practices might be questioned, and individual patient factors might make a difference. In this study by Perrot and Bertin, patient acceptable symptom state (PASS) and minimally clinically important improvement (MCII) were variously influenced by patient sex, age, body weight, and baseline pain. Generally, younger, nonobese males, with lower baseline levels of pain at rest showed the greatest improvement.
The researchers determined the MCII as a 1-point decrease on NRS; whereas, others have found 2 points as defining what they called “minimal important change (MIC)” from the patient’s perspective [Ostelo et al. 2008]. Additionally, some researchers have claimed that 1.2 points to 1.4 points (12-14 mm on VAS) establish the “minimum clinically significant difference (MCSD)” for patients to distinguish whether pain is becoming “a little better” or “a little worse” over time [Kelly 2001; Strøm et al. 2012]. However, these observations were not specifically in patients with osteoarthritis and, although such small changes in pain score may be statistically significant in research outcomes data, they are likely to be of minor clinical importance.
What would be clinically important? After examining a range of outcome measures to assess back pain, Ostelo and colleagues  concluded that a 30% decline in pain score from baseline may be considered as a clinically meaningful improvement. In the present study of knee/hip osteoarthritis by Perrot and Bertin , despite the large effect sizes for improvement in pain NRS scores, patients achieved that 30% goal for pain during motion (37% improvement) but not at rest (22% improvement). So accepting an NRS score of <4.0 at rest as denoting an acceptable threshold of pain for patients to “feel well” may not translate to clinically important improvement.
Of course, there are many factors that may interact in patients’ pain perceptions, their responses to therapy and expectations for pain relief, and the level of pain that is acceptable for them to believe that they are “feeling well.” Scores on pain-assessment scales can be helpful as a guide, as long as healthcare professionals remember that they are treating patients not numbers.
The present study by Perrot and Bertin was very short-term and patient expectations as well as responses to therapy, with potentially emerging adverse events, would probably change during a longer period of followup. Further research should investigate these issues in long-term trials, ideally using a randomized, controlled design.
> Kelly A-M. The minimum clinically significant difference in visual analogue scale pain score does not differ with severity of pain. Emerg Med J. 2001;18:205-207 [available here].
> Ostelo RWJG, Deyo RA, Stratford P, Waddell G, Croft P, von Korff M, Bouter LM, de Vet HC. Interpreting change scores for pain and functional status in low back pain: Towards international consensus regarding minimal important change. Spine 2008;33(1):90-94 [abstract].
> Perrot S, Bertin P. “Feeling better” or “feeling well” in usual care of hip and knee osteoarthritis pain: Determination of cutoff points for patient acceptable symptom state (PASS) and minimal clinically important improvement (MCII) at rest and on movement in a national multicenter cohort study of 2414 patients with painful osteoarthritis. PAIN. 2013;154(2):248-256 [abstract here].
> Strøm V, Røe C, Knardahl S. Coffee intake and development of pain during computer work. BMC Research Notes. 2012(Sep 3);5:480 [available here].
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