Reliability of the nociceptive withdrawal reflex threshold and the electrical pain threshold of chronic pain patients in a clinical environment

J.A. BIURRUN MANRESA; Y. GHAMRI; O.K. ANDERSEN; M. CURATOLO

Milán

Congreso; 14th World Congress on Pain; 2012

Aim of Investigation: Normative values and test-retest reliability for the nociceptive withdrawal reflex threshold (NWR-T) and the electrical pain threshold (EP-T) in pain-free subjects and chronic pain patients have recently been published, concluding that both measurements are reliable in experimental pain studies. However, it is necessary to investigate the reliability of the NWR-T and EP-T in clinical conditions, which often present significant differences compared to a research environment. Typical example would be the larger differences between patients and limited number of times that an assessment can be repeated for each outcome variable, given the time constrains commonly found in the clinic. Thus, the aim of this study was to establish the reliability of the NWR-T and EP-T in a clinical environment.Methods: Two hundred and fifty eight patients with chronic pain (110 men and 148 women, mean age 51 years, range 16?88 years) participated in the study. They were consecutive patients derived from the Pain Clinic at Inselspital (Bern, Switzerland). In order to assess the NWR-T and EP-T, electrical stimulation was performed through surface electrodes placed caudal to the lateral malleolus, at the innervation area of the sural nerve, and the reflex response was assessed at the biceps femoris muscle. Both thresholds were assessed three consecutive times (with a 10-30 s interval between assessments), and median values were derived. Kruskal-Wallis One Way ANOVA (KW) was performed to compare the three assessments and the median for each variable, and Coefficient of Variation (CV) and Coefficient of Repeatability (CR) were used to assess reliability. All results are presented as mean ± SD.Results: The NWRT-T after three assessments were 9.0 ± 5.4 mA, 9.2 ± 5.5 mA and 9.5 ± 5.6 mA, respectively; and the median NWRT-T was 9.3 ± 5.3 mA. The EP-T after three assessments were 6.8 ± 3.7 mA, 7.2 ± 4.0 mA and 7.3 ± 4.1 mA, respectively; and the median EP-T was 7.1 ± 3.9 mA. KW test revealed that there were no significant differences between the three assessments and the median for the NWR-T (H = 0.96, df=3, p = 0.81) or the EP-T (H = 3.60, df = 3, p = 0.30). Average CV was 18.7% for NWR-T and 11.8% for EP-T, whereas average CR was 4.8 mA for NWR-T and 2.3 mA for NWR-T.Conclusions: The statistical analysis showed that it is not necessary to repeat the NWR-T and EP-T assessment three times, since there is no statistical difference among the three consecutive assessments, or between any of the assessments and the median. The reliability of the NWR-T and EP-T was lower compared to previous results on experimental conditions, probably due to larger variations in the chronic pain population or differences in the assessment methodology. However, their current reliability levels are still acceptable for clinical use.