How can we reliably measure pain sensitivity?
Full reference: Brady S, Georgopoulos V, Veldhuijzen van Zanten JJCS, Duda JL, Metsios GS, Kitas GD, Fenton SM, Walsh DA, McWilliams DF. The inter-rater and test-retest reliability of three modalities of Quantitative Sensory Testing in healthy adults and people with chronic lower back pain or rheumatoid arthritis. PAIN Reports 2023; 8(6):p e1102, doi: 10.1097/PR9.0000000000001102.
The central nervous system (brain and spinal cord) plays a hugely important role in pain. The processing of pain signals can worsen the pain from many different body sites, across many different diagnoses, in many different people. Measuring the effects of the central nervous system is challenging, but a series of physical tests can be used that measure pain sensitivity; Quantitative Sensory Testing.
This study tried to find out if different tests can reliably measure pain sensitivity in people with rheumatoid arthritis, people with chronic lower back pain and healthy volunteers.
The tests measured different aspects of pain processing by the central nervous system. The tests were called Pressure Pain detection Threshold (sensitivity to painful pressure), Temporal Summation (feelings from repeated prodding with a bristle), and Conditioned Pain Modulation (how pain at one site can change how pain is felt elsewhere). Each test involved participants experiencing brief pain. Several groups of people volunteered for the study. They had rheumatoid arthritis (18), chronic low back pain (25) or were healthy volunteers (45). Different groups had their pain sensitivity measured on their forearms or on their lower leg. Pain sensitivity tests were repeated by different researchers, and also on different days.
The measurements from Pressure Pain detection and Temporal Summation tests gave consistent results on different days and also when different researchers performed the tests and in all groups of people. These tests are very suitable to be used in studies of different conditions and in studies conducted by different researchers in different centres. Meaningful comparisons between different studies that use these tests should be possible.
The Conditioned Pain Modulation tests did not consistently give the same results when repeated, whether by the same or by different researchers. We should be cautious about comparing results between different researchers or research studies. However, it might be that Conditioned Pain Modulation varies from moment to moment within an individual, and that a single measurement gives only a poor indication of this aspect of how their central nervous system processes pain.