Memory for Pain: Implications for Treatment and Research

The accuracy of pain recall has important implications for both clinical management and clinical trials in situations where pain is a prominent or primary symptom (or outcome measure). In this post, I share a few thoughts from the literature and my own research about the accuracy of remembered pain, and the benefits and limitations of relying on patient’s memory for pain.

Pain is a major public health problem, resulting in personal suffering, reduced productivity, and increased health care costs. A report from the National Academy of Medicine states that chronic pain affects approximately 100 million adults in the U.S. and costs the economy over $600 billion annually. This includes $300 billion in direct health care costs and a further $300 billion in lost productivity. Common pain states such as low back pain, osteoarthritis, painful diabetic neuropathy, fibromyalgia, and headache are the leading causes of disability for individuals of working age.

Clinical management of pain requires a careful assessment of its history, including frequency, intensity, duration and quality, as well the impact of pain on activities of daily living. The accuracy and reliability of a patient’s pain recall are key to the diagnosis and treatment of many acute and chronic conditions, and increasingly on outcomes assessment. Unfortunately, clinicians have little choice but to rely almost entirely on their patients’ retrospective self-report of pain, sometimes over a period of weeks and even months. This is the cause of some consternation to many clinicians. Similarly, in clinical trials, where patient follow-up visits may occur as infrequently as every four to six weeks, there is a concern about the validity of retrospective pain reports. Even when pain intensity or relief are recorded daily, such data are generally retrospective in nature, to the extent that they capture pain recall over hours or even days, rather than pain as it occurs. Similarly, we continue to use weekly or monthly scores for patient reported outcomes such as the patients’ global impression of change (PGIC) and the patients’ global impression of severity (PGIS).

My former colleague, Dr. Andrew Darke and I studied the accuracy of patients’ recall of the pain experience in 77 hospitalized patients who had undergone orthopedic surgery. After surgery, under study coordinator supervision, patients were asked to record their pain intensity every hour for 48 hours. They were also asked to retrospectively rank their worst, least, and average pain intensity at the 24 and 48-hour mark. Our research showed that worst, least, and average pain intensity recall at 24 and 48 h were highly correlated with experienced maximum, minimum, and mean pain intensity from hourly reports, respectively. The results of our study suggest that (i) memory for pain is both accurate and reliable many acute postsurgical pain settings; and (ii) pain recall instruments may be a useful alternative in settings where hourly pain assessments are impractical.

Studies by Dr. Mark Jensen, Professor and Vice Chair for Research in the Department of Rehabilitation Medicine at the University of Washington have also demonstrated that individual recall and composite scores of pain intensity recall are generally reliable and valid measures of actual pain in patients with cancer pain. In another study, Dr. Jensen’s team observed that 24-hour pain recall scores were valid indicators of average postsurgical pain scores. These findings also support the potential use of pain recall as an outcome measure in clinical trials.

Other clinical studies that have provided longer term data consistent with our findings include work by Dr. Jennifer Bolton, Vice-Principal for Postgraduate Studies and Research at the AECC University College in Bournemouth, UK, and Dr. Marta Meana, Dean and Professor of Psychology at University of Nevada Las Vegas.

In Dr. Bolton’s study, 78 patients presenting to a chiropractic outpatient clinic with nonspecific neck pain recorded pain intensity 4 times a day on an 11-point numerical rating scale for 7-days and their recall of average, worst and least pain over the previous week on Day-8. She observed that “recall of average pain over the previous week was a valid measure using ratings of actual pain as the criterion standard” and “patients were also able to accurately recall their pain at its worst and at its least over the preceding week”. Dr. Bolton concluded that “recall ratings of pain intensity may be valid for use in clinical research and practice on patients with nonspecific neck pain”.

Dr. Meana’s study of a 100 women with endometriosis is of particular importance because diagnosis and treatment decisions for endometriosis continue to be guided by pain intensity, despite the inconsistent relationship between pain and verifiable organic pathology. Dr. Meana observed that women with endometriosis were “generally quite accurate in their recall of pain experienced over the previous 30 days” and that “physicians may rest assured that the report of pain they are obtaining from the majority of patients is relatively accurate”.

Although the validity of retrospective pain reports is suspect in the eyes of some, available data would suggest that in a majority of adult patients and clinical settings, recall of acute and chronic pain is generally accurate and reliable. Pain intensity outcomes can utilize recall questions when actual pain reports (or more frequent reports) are impractical. However, there is a need to exercise caution against excessive reliance on remembered pain in clinical trials since exclusive use of this method results in the loss of information about the time course of pain and analgesia (e.g., onset, peak. and duration of effect). Furthermore, in clinical trials of analgesics, infrequent pain reports reduces the ability to correlate pharmacodynamic variables with the pharmacokinetic behavior of the analgesics under study.

Dr. Najib Babul, PharmD, MBA, is an experienced drug development consultant with extensive experience in new [505(b)(1)] and repurposed [5050(b)(2)] oral, intravenous, transdermal and intranasal drugs to market. A graduate of the University of British Columbia, the State University of New York, and the California Institute of Advanced Management, he has over two decades of experience in bringing new drugs to market.

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