A myriad of methods to determine temporal summation of pain in people with musculoskeletal pain and healthy participants: a scoping review

Abstract

Temporal summation of pain (TSP) is a human proxy for wind-up of dorsal horn neurons as assessed in animals. The common paradigm for eliciting TSP is evoked by repetitive nociceptive stimuli of equal intensity. Various stimulation and assessment protocols have been used. This scoping review aims to provide insight into key elements of TSP stimulation and assessment: modality, instruments, test location, familiarization, train characteristics, and calculations. PubMed, Embase, and Ebsco/CINAHL were searched for studies that measured TSP in adults with musculoskeletal conditions and healthy people. Four hundred six studies were included. Mechanical stimuli were the most commonly used modality (250 studies), followed by thermal stimuli (125 studies). Forty-six different instruments were used. Disregarding studies on widespread musculoskeletal pain and healthy participants, 40 studies evaluated TSP at painful sites, 77 in remote areas, and 66 in both locations. Of the 13 tested locations in patients, the hand (74 studies), lower leg (64 studies), and forearm (59 studies) were most commonly tested. A single practice round was the most common familiarization method (46 studies). Repeated stimuli were applied using 31 different frequencies (0.03-200 Hz) and sustained stimulations ranging from 5 to 1080 seconds were used. Twenty-two different train lengths, 63 different calculations (37 absolute, 19 relative, and 7 alternatives using data directly), and 14 different outcome measures (eg, self-reported pain rating scales and reflex thresholds) were used. Temporal summation of pain protocols vary excessively, hindering the comparison and pooling of results. None of the studies provided substantiation for their protocol choice.

Keywords: Pain measurement; Pain modulation; Pain perception; Quantitative sensory testing; Temporal summation of pain; Wind-up ratio.

Figure 1.

Flow diagram of the search strategy. Results for studies on TSP and musculoskeletal conditions. TSP, temporal summation of pain.

Figure 2.

Modality, frequency, and train length. Shankey diagram showing the link between the number of TSP studies per modality, frequency, and train length used to measure TSP. Continuous, sustained-stimulation; Reps, repetitions. The node and path sizes linked to each modality, frequency, and train length were scaled to allow direct comparison within the figure. TSP, temporal summation of pain.

Figure 3.

Absolute calculations and statistical comparisons. Shankey diagram showing the link between the number of studies per modality, absolute calculation, statistical comparisons, no calculations, and the type of outcome measure used to measure TSP. The description of the calculations was shortened to improve the visual presentation. For example, “[last] minus [first]” stands for “the intensity following the first stimulus is subtracted from the intensity of the last stimulus of the train.” The node and path sizes linked to the modality, calculation, statistical comparisons, and outcome measures are scaled and matched with those of Figure 4 to allow for direct comparison. TSP, temporal summation of pain.

Figure 4.

Relative calculations. Shankey diagram showing the link between modalities, relative calculation, statistical comparisons, no calculations, and outcome measures used to measure TSP. The different calculations have been shortened to give a better visual presentation, for example: “[mean last of all trains] divided by [mean of all singles]” stands for “the mean of the last stimuli of every train is divided by the mean of all singles that were assessed before each train.” AUC, area under the curve; eVAS, electronic visual analog scale; NRS, numeric rating scale; TSP, temporal summation of pain; VAS, visual analog scale. Node and path sizes linked to modality, calculations, no calculations, and outcome measures are scaled and match those of Figure 4 to allow for direct comparison.