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To investigate the normal data of pain-related evoked potentials (PREP) elicited with a concentric surface electrode among normal, healthy adults and the relationship between PREP and pain intensity.
Sixty healthy volunteers (22 men and 38 women; aged 36.4±10.7 years; height, 165.4±7.8 cm) were enrolled. Routine nerve conduction study (NCS) was done to measure PREP following electrical stimulation of hands (C7 dermatome) and feet (L5 dermatome). Negative peak (N), positive peak (P) latencies, peak to peak (NP) amplitudes, conduction velocity (CV), and verbal rating scale (VRS) score were obtained. Linear regression analysis tested for significant relevance between variables of PREP and VRS score.
Normal NCS results were obtained in all subjects. N latency of hand PREP was 163.8 ±40.0 ms (right) and 161.0±39.9 ms (left). N latency of foot PREP was 178.0±43.9 ms (right), 180.4±43.4 ms (left). NP amplitude of hands was 20.6±10.6 µV (right) and 21.9±11.6 µV (left). NP amplitude of feet was 18.8±8.3 µV (right) and 19.0±8.4 µV (left). The calculated CV was 13.2±4.7 m/s and VRS score was 3.8±1.0. A highly significant positive correlation was evident between VRS score and NP amplitude (y=0.1069x+1.781, r=0.877, n=60, p<0.0001).
PREP among normal, healthy adults revealed a statistically significant correlation between PREP amplitude and VRS score.
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To evaluate the clinical utility of the electrically calculated quantitative pain degree (QPD) and to correlate it with subjective assessments of pain degree including a visual analogue scale (VAS) and the McGill Pain Questionnaire (MPQ).
We recruited 25 patients with low back pain. Of them, 21 patients suffered from low back pain for more than 3 months. The QPD was calculated using the PainVision (PV, PS-2100; Nipro Co., Osaka, Japan). We applied electrodes to the medial forearm of the subjects and the electrical stimulus was amplified sequentially. Minimum perceived current (MPC) and pain equivalent current (PEC) were defined as minimum electrical stimulation that could be sensed by the subject and electrical stimulation that could trigger actual pain itself. To eliminate individual differences, we defined QPD as the following: QPD=PEC-MPC/MPC. We scored pre-treatment QPD three times at admission and post-treatment QPD once at discharge. The VAS, MPQ, and QPD were evaluated and correlations between the scales were analyzed.
Result showed significant test-retest reliability (ICC=0.967, p<0.001) and the correlation between QDP and MPQ was significant (at admission SRCC=0.619 and p=0.001; at discharge SRCC=0.628, p=0.001). However, the correlation between QPD and VAS was not significant (at admission SRCC=0.240, p=0.248; at discharge SRCC=0.289, p=0.161).
Numerical values measured with PV showed consistent results with repeated calculations. Electrically measured QPD showed an excellent correlation with MPQ but not with VAS. These results demonstrate that PV is a significantly reliable device for quantifying the intensity of low back pain.
Citations
Objective: The aim of the present study was to investigate the pain intensity, quality, and pattern in experimental muscle pain.
Method: Eleven healthy adults and eleven myofascial pain syndrome (MPS) patients participated in this study. Hypertonic saline (5%) was injected into upper trapezius, infraspinatus and tibialis anterior muscles of 11 healthy adults. A continuous recording of ongoing pain intensities of the local pain and referred pain was measured. After pain had subsided, the subjects completed a Korean version of the McGill Pain Questionnaire (MPQ). This study included 11 patients who have trigger point on upper trapezius muscle. Pain pressure thresholds (PPTs) and pain intensity ratings of different pressure stimuli in upper trapezius muscles were compared with experimental group.
Results: In experimental group, local pain became maximal after one minute and referred pain after one and a half minutes. At that time, Visual analogue scale (VAS) score was 3.8 and 1.9 each other. The referred pain of upper trapezius muscle primarily radiated to the posterolateral side of neck. The one of infraspinatus muscle radiated to the shoulder joint and anterolateral side of upper arm area and the one of tibialis anterior muscle radiated to the shin and dorsum of ankle joint. The PPTs were found to be significantly lower in upper trapezius muscle of patients with myofascial pain syndrome (MPS) than in those of experimental group. The slope of VAS to different stimuli showed the linear relationship at both group, and in that of patient groups was found to be significantly steeper than in that of experimental group. The experimental muscle pain group had no difference in pain quality compared with MPS patients except affective subscale.
Conclusion: The present results suggest that intramuscular injection of hypertonic saline can be used a experimental pain model of MPS, and PPTs and pain intensity ratings of different pressure stimulus are valuable tools for quantitative description of chronic and experimental muscle pain.
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