Mechanical and heat hyperalgesia highly predict clinical pain intensity in patients with chronic musculoskeletal pain syndromes

Abstract

Multiple abnormalities in pain processing have been reported in patients with chronic musculoskeletal pain syndromes. These changes include mechanical and thermal hyperalgesia, decreased thresholds to mechanical and thermal stimuli (allodynia), and central sensitization, all of which are fundamental to the generation of clinical pain. Therefore, we hypothesized that quantitative sensory tests may provide useful predictors of clinical pain intensity of such patients. Our previous studies of fibromyalgia (FM) patients have shown statistically significant correlations of quantitative sensory test results with clinical pain intensity, including mechanical spatial summation, number of pain areas, wind-up, and wind-up aftersensations. Although these tests predicted up to 59% of the variance in FM clinical pain intensity, their expense and technical complexities limited widespread use in clinical practice and trials. Thus, we developed practical tests of primary (mechanical) and secondary (heat) hyperalgesia that also strongly predict clinical pain intensity in patients with chronic musculoskeletal pain disorders. Thirty-six individuals with FM, 24 with local musculoskeletal pain, and 23 normal controls underwent testing of mechanical and heat hyperalgesia at the shoulders and hands. All subjects rated experimental pains using an electronic visual analog scale. Using either heat or pressure pain ratings as well as tender point counts and negative affect as predictors, up to 49.4% of the patients' variance of clinical pain intensity could be estimated. Results of this study emphasize the important contributions of peripheral and central factors to both local and widespread chronic pain. Overall, measures of mechanical and heat hyperalgesia in combination with tender point and negative affect provided powerful predictors of clinical pain intensity in chronic musculoskeletal pain patients that can be readily used in clinical practice and trials.

Perspective: Simple tests of mechanical and heat hyperalgesia can predict large proportions of the variance in clinical pain intensity of chronic musculoskeletal pain patients and thus are feasible to be included in clinical practice and clinical trials.

Figure 1

Time course of pressure and heat pulses used at the shoulders and hands. The solid line represents the time course of either 200 kPa pressure or 44°C heat pulses. Duration of all experimental pain stimuli was 10 seconds. Pressure increased from baseline (0 kPa) to peak levels (200 kPa) in 6 seconds. Subsequently, they remained at peak levels for 4 seconds. Similarly heat pulses increased from baseline (38°C) to peak levels (44°C) in 6 seconds and remained at peak levels for 4 seconds.

Figure 2

Clinical pain ratings of all study subjects using a mechanical VAS (0–100). Mean (SD) pain ratings of LMP and FM subjects were 29.3 (23.4) and 46.8 (25.0), respectively. NC subjects reported only minimal incidental pains. Clinical pain ratings significantly differed among all groups (P < .001).

Figure 3

Shoulder and hand pain ratings of all subjects during pressure stimuli. Experimental pressure stimuli were applied to the middle of the shoulders (trapezius muscle) or to the space between the first 2 fingers using an electronic algometer. After 10 seconds of 200-kPa pressure pain, ratings of FM subjects were significantly higher than either NC or LMP subjects. No significant differences in pressure pain ratings were noted between NC and LMP subjects (P > .05). Similar results were found at the hands.

Figure 4

Shoulder and hand pain ratings of all subjects during heat stimuli. 10 seconds heat stimuli were applied to the skin overlying the middle of the trapezius muscles or to the thenar eminence of the hands. Experimental pain ratings of FM subjects at the shoulders were significantly higher at 44°C than NC or LMP subjects (P < .01). However, there was no significant difference between heat pain ratings of LMP and NC subjects (P > .05). Similar findings were obtained at the hands.