Sensory phenotypes in patients with peripheral neuropathic pain evaluated with quantitative sensory testing

Abstract

Abstract Background In patients with neuropathic pain, Quantitative Sensory Testing (QST) can define different sensory phenotypes thought to be related to different underlying mechanisms. One phenotype with abnormal sensitization of cutaneous nociceptors has been termed irritable nociceptors. Methods This study is a part of a randomized, double-blind, placebo controlled, crossover trial with the anticonvulsant oxcarbazepine. The study is ongoing. In this report, baseline QST measures from patients with peripheral neuropathic pain due to either polyneuropathy (PNP) or peripheral nerve injury (PNI) are analyzed. QST evaluates thresholds for cold and heat detection (CDT, WDT), thermal pain (CPT, HPT), vibration (VDT), pin prick, mechanical detection and pressure pain. Furthermore, wind-up ratio and dynamic mechanical allodynia (DMA) are evaluated. Patients with irritable nociceptors are defined as patient with normal CDT and WDT and either mechanical or thermal allodynia or hyperalgesia. Results By March 2012, 28 patients with PNI and 24 with PNP were included. There was no difference in pain duration (66.2 (53.7) vs. 64.0 (43.3) months, p = 0.87) or pain intensity (NRS, 0 10) (6.6 (1.6) vs. 6.3 (1.7), p = 0.54), but patients with PNI were significantly younger (48.8 (15.1) years) compared to patients with PNP (62.4 (8.5) years), p < 0.001. The percentage of irritable nociceptors in the PNI group was 39.3% and in the PNP group 29.2% (p = 0.44). The percentage of patients with DMA was 39.3% and 33.3%, respectively (p = 0.66). Significantly more patients with PNI had thermal allodynia (28.6% vs. 0%, p = 0.005), 6 reported cold allodynia and 4 heat allodynia. Conclusion Preliminary results show that there was no significant difference in percentage of irritable nociceptors between the two groups, but more patients with PNI had thermal allodynia.