Painless Electrodiagnostic Current Perception Threshold and Pain Tolerance Threshold Values in CRPS Subjects and Healthy Controls: A Multicenter Study

Abstract

Abstract: The purpose of this study is to evaluate both painless and painful sensory transmission in patients with Complex Regional Pain Syndrome (CRPS) using the automated electrodiagnostic sensory Nerve Conduction Threshold (sNCT) test. This test generates reliable, painless Current Perception Threshold (CPT) and atraumatic Pain Tolerance Threshold (PTT) measures. Standardized CPT and PTT measures using constant alternating current sinusoid waveform stimulus at 3 different frequencies 5 Hz, 250 Hz, and 2 kHz (Neurometer® CPT/C Neurotron, Inc. Baltimore, MD) were obtained from CRPS subjects at a distal phalange of the affected extremity and at an ipsilateral asymptomatic control site. Matched sites were tested on healthy subjects. Detection sensitivities for an abnormal PTT and CPT test were calculated based on specificity of 90% as determined from data obtained from healthy controls. A Spearman rank correlation was used to test for a significant association between presence of allodynia and an abnormal PTT or CPT at any frequency tested. Thirty‐six CRPS subjects and 57 healthy controls were tested. The highest detection sensitivity of the PTT test from symptomatic test sites was 63% for the finger and 71% for the toe. PTT abnormalities were also detected, to a lesser degree, at the asymptomatic control site (41% finger control site, 16% toe control site). The highest CPT detection sensitivity at the symptomatic site was 37% for the finger site and 53% for the toe site. CPT abnormalities were also detected at the asymptomatic control site (29% finger control site, 37% toe control site). Eighty‐six percent of the CRPS subjects had either a PTT or CPT abnormality at any frequency at the symptomatic site. There was a significant correlation between presence of allodynia and presence of an abnormal CPT and PTT, respectively (P < .01). The correlation coefficient was lower for CPT than for PTT, ie, 0.34 versus 0.6 for the finger and 0.48 versus 0.67 for the toe, respectively. In studied CRPS patients an abnormal PTT was detected with higher sensitivity than an abnormal CPT. Assessing PTT may become a useful electrodiagnostic quantitative sensory test for diagnosing and following the course of neuropathic pain conditions.