We use quantitative sensory testing (QST) to explore how somatosensory information is processed in the nervous system in people with painful conditions such as low back pain, fibromyalgia, and irritable bowel syndrome. QST has shown promise for clinical applications such as evaluating responses to interventions (Grosen, Fischer et al. 2013), patient profiling and monitoring somatosensory dysfunctions over time (e.g. in neuropathic pain) (Backonja, Attal et al. 2013). When we interpret these findings, we assume that QST responses are stable and reproducible, even when repeated after longer periods of time… But is that the case?
To answer this question, we performed a test-retest reliability study assessing 42 pain-free volunteers (50% females) on three occasions over a 4 month period (Marcuzzi, Wrigley et al. 2017). We investigated two categories of QST: static and dynamic tests. For the static tests, we used standardised methods to assess thermal and mechanical thresholds (e.g. pressure pain threshold, cold and heat thresholds, two-point discrimination). For the dynamic tests, we evaluated temporal summation and conditioned pain modulation (CPM). Tests were performed both at the back and at the hand, except for CPM which was performed using a cold water bath at the foot (conditioning stimulus) and heat pain and pressure pain at the upper arm (test stimuli).
We found that static QST have high reliability (ICCs: 0.68-0.90) which indicates that they are suitable for monitoring individuals over time, even when tests are repeated after months. However, dynamic QST, particularly CPM, are less stable over time (ICCs: 0.35-0.61). This is perhaps not surprising as dynamic tests involve the assessment of complex mechanisms of nociceptive modulation which might be subjected to physiological variability over time, while static QST provide a measure of the basal state of the nervous system involving a reproducible endpoint (i.e. threshold).
We also know that one important factor that can affect the reliability of QST measures is methodological difference in protocols, particularly for CPM testing (Pud, Granovsky et al. 2009). This is supported by our results as we found that CPM test reliability using heat pain as the test stimulus was superior to pressure pain. Therefore, establishing an optimal protocol for CPM testing should be a priority in future research to improve test reliability and its clinical application.
Interestingly, we also observed a small but systematic change in mechanical tests and CPM effect: i.e. people becoming “more sensitive” over time. However, thermal pain thresholds did not show this trend over time. It is possible that the changes in mechanical tests and CPM effect over time may reflect a learning effect. These findings indicate that caution needs to be taken when interpreting longitudinal changes associated with these measures.
It is also important to highlight that substantial variability was observed in QST responses, particularly for tests performed at the back. This means that considerable changes need to occur to be able to rule out that these are due by chance. We report on the minimal detectable differences for each of the QST in the published paper of this study (Marcuzzi, Wrigley et al. 2017). This is important information for clinicians and researchers looking to identify clinically meaningful changes in somatosensory function over longer periods in individual patients.
About Anna Marcuzzi
Anna has a background in physiotherapy. She is currently a postdoc researcher at the Pain Management Research Institute, Kolling Institute (University of Sydney). This study was completed as part of her PhD at Macquarie University, Sydney, with A/Professor Julia Hush. Her research focuses on musculoskeletal pain and understanding neurophysiological mechanisms in the development of chronic pain. When not in the office she likes to try all sorts of outdoors activities that Sydney has to offer.
References
Backonja, M. M., et al. (2013). “Value of quantitative sensory testing in neurological and pain disorders: NeuPSIG consensus.” Pain 154(9): 1807-1819.
Grosen, K., et al. (2013). “Can quantitative sensory testing predict responses to analgesic treatment?” European Journal of Pain 17(9): 1267-1280.
Marcuzzi, A., et al. (2017). “The long-term reliability of static and dynamic quantitative sensory testing in healthy individuals.” Pain 158(7): 1217-1223.
Pud, D., et al. (2009). “The methodology of experimentally induced diffuse noxious inhibitory control (DNIC)‐like effect in humans.” Pain 144(1-2): 16-19.