An updated view on the reliability of different protocols for the assessment of conditioned pain modulation

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In the recent review on test–retest reliability of conditioned pain modulation (CPM) by Kennedy et al.4 published in PAIN (November 2016, Volume 157, Issue 11), different CPM reliability studies were summarized. In the 10 studies included in the review, the most commonly investigated test stimulus (TS) was pressure pain threshold (5 studies), followed by contact heat pain (3 studies). Further, the most common conditioning stimulus (CS) was cold water immersion (6 studies) followed by hot water immersion (3 studies) and ischemic pain (3 studies). Overall, the reliability of the TS and TS in combination with CS were good (intraclass correlation coefficient [ICC] > 0.6) to excellent (ICC > 0.75). The systematic search, which formed the basis for the review, was performed on August 26, 2015. Recently, cuff algometry has been suggested as a user-independent method for assessment of pain sensitivity and CPM.1–3,5 Briefly, cuff algometry assesses pain sensitivity and CPM using 2 inflatable tourniquet cuffs, where one cuff serves as the TS assessing cuff pressure pain threshold and cuff pressure pain tolerance and the other cuff induces the CS. Since August 26, 2015, 4 studies1–3,5 have addressed the reliability of CPM assessed with cuff algometry. Three studies investigated healthy controls (total number of subjects: 171) and 1 study investigated chronic pain patients (total number of subjects: 400).
Firstly, Graven-Nielsen et al.1 studied different cuff CPM protocols for their influence on CS intensity, duration, and location at baseline and at 1-month follow-up in 20 pain-free subjects. For TS on the lower leg ICC >0.75 (excellent reliability), for TS on the lower leg in combination with CS on the opposite lower leg ICC >0.75 (excellent reliability), and for the calculated CPM effect ICC >0.6 (good reliability).
Secondly, Imai et al.3 compared 5 different TS modalities (electrical, heat, handheld algometry, cuff pressure pain threshold, and cuff pressure pain tolerance) and 2 different CS (cold pressor test [CPT] and cuff algometry) in 26 pain-free subjects. The study investigated within and between session reliability where sessions were divided by 1 to 3 weeks. The largest CPM effect and the most reliable combination was achieved by handheld algometry as TS and CPT as CS. Reliability for cuff algometry as TS demonstrated ICC >0.75 (excellent reliability) and coefficient of variation (CV) <18%. Moreover, reliability for cuff algometry as TS during cuff CS showed ICC >0.75 (excellent reliability) and CV <18%.
Thirdly, Graven-Nielsen et al.2 investigated CPM in 125 pain-free subjects using the cuff algometry as TS and the CPT as CS. Intersession reliability of cuff algometry demonstrated an ICC >0.75 (excellent reliability) and CV <18%. Further, the study suggested that cuff algometry as TS was not significantly influenced by gender and age.
Finally, Vaegter and Graven-Nielsen5 investigated temporal summation of pain and CPM profiles in 400 patients with chronic pain. Intrasession reliability of cuff algometry as TS showed ICCs >0.75 (excellent reliability) and intrasession CV <19%.
In addition to the impressive work done by Kennedy et al.,4 these recent studies suggest that cuff algometry is a reliable user-independent method for assessing pain sensitivity and CPM in healthy controls and chronic pain patients.
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