We know low back pain (LBP) is a condition with a variable prognosis. A good proportion of people recover quite quickly from an episode of LBP, but some will have fluctuating symptoms or develop chronic LBP . Currently, there is no consensus as to which factors are more important to predict this trajectory . Psychosocial (e.g. distress) and pain-related features (e.g. pain severity) are the most commonly investigated and considered strong prognostic factors in LBP, but they still only explain a limited proportion of the variance (e.g. up to 40% at best) of LBP outcomes .
We recently published a systematic review  to specifically investigate the prognostic utility of Quantitative Sensory Testing (QST) in LBP. QST is a psychophysical method that enables assessment of the function of the somatosensory nervous system and quantification of the evoked responses through the delivery of various standardised stimuli (e.g. pressure, cold and touch). The widespread use of QST in recent decades has provided useful insights in pain research such as characterising somatosensory profiles or changes in musculoskeletal conditions, including LBP. Recent studies demonstrated a promising application of QST as a prognostic tool in musculoskeletal conditions (e.g. whiplash injury and epicondylalgia) [1,7,8]. This led us to interrogate if QST can predict the course of LBP.
We included prospective longitudinal studies assessing participants with non-specific LBP (i.e. exclusion of LBP arising from serious pathologies or specific conditions, e.g. pregnancy, fibromyalgia) for at least one QST measure. Studies had to report LBP status at follow up as well as a measure of its association with QST variables. No restrictions were placed on setting or the recruitment source of participants. We excluded studies of LBP after back surgery. The outcomes of interest were LBP status at follow up, including pain intensity, clinically significant pain, disability, work status, global perceived recovery, and health-related quality of life.
We performed a systematic and comprehensive literature search of 6 databases. To our surprise, very few studies have investigated the prognostic value of QST in LBP, and only 3 studies were eligible, of which two recruited participants from primary care and one from tertiary care (pain clinic). One study assessed participants with acute LBP, while the other two assessed participants with chronic LBP.
So…can QST responses predict the course of LBP?
The QST measures assessed in these studies included pressure and cold pain testing, dynamic measures of temporal summation of pain and conditioned pain modulation. Answering our question, the studies showed that none of these variables was significantly predictive of clinically significant pain at 4 months (in acute LBP), and pain intensity at 1 year and work ability at 2 years (in chronic LBP).
What can be done next?
At present, there is not sufficient evidence to determine whether QST responses are predictive of LBP outcomes. Indeed, the limited evidence available suggests that they are not. Nonetheless, further investigations of QST as a prognostic tool may be worthwhile. Future studies should attempt to overcome the limitations identified in the studies included in this review. For example, the included studies used survivor cohorts, which means that the individuals assessed were at different points in the course of their LBP (e.g. in one study individuals had LBP with a mean duration of 9.6 years and standard deviation of 8.8). Factors that predict the course of LBP are unlikely to be the same in people who are at different stages of the condition. Future studies should therefore recruit individuals at a uniform point in the course of their LBP. Another limitation of using QST tests in prognostic studies is related to reliability, which is affected by, among others, environmental and methodological factors. In the included studies information about the QST tests procedures (e.g. patients positioning, order of the test, blinding of assessors, standardized instructions) were mostly not reported. It is therefore important that QST tests are performed in a standardised way to minimise variability of responses which would otherwise dilute prognostic information .
Knowledge is now accumulating about somatosensory changes that characterise early stages of LBP. This will be useful to inform the selection of QST measures for future prospective studies. For example, we previously identified cold pain sensitivity to be associated with people with higher levels of pain intensity compared to those with mild pain in people with acute LBP (Marcuzzi et al (2016) “Quantitative sensory test responses are similar in acute back pain and pain-free groups, but cold pain sensitivity distinguishes individuals with different pain severity” under review). It would be also useful to assess the prognostic ability of QST responses in combination with known psychosocial, demographic and pain-related predictors to account for the heterogeneity of LBP.
About Anna Marcuzzi
Anna Marcuzzi is a physiotherapist who graduated from the University of Parma (Italy). She worked clinically in the musculoskeletal area for 5 years while accomplishing a Masters in Sport Physiotherapy (University of Pisa). Anna has recently submitted her PhD thesis from Macquarie University (Sydney) under the supervision of A/Prof Julia Hush with a project investigating longitudinal somatosensory changes in acute low back pain. While she loves climbing mountains and bike riding, she has yet to acclimatise to the aquatic life of Australia.
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Commissioning Editor: Neil O’Connel; Associate Editor: JP Caneiro