Reflections of the sensory findings in the central nervous system in patients with neuropathic pain

Abstract

This study aimed to evaluate whether there was a difference in functional magnetic resonance imaging (fMRI) findings in patients who were found having hyperalgesia or hypoesthesia according to Quantitative Sensory Tests (QST). Forty participants were included in the study: 20 with neuropathic pain (NP) due to cervical disc pathology (NP group) and 20 healthy volunteers. After obtaining the socio-demographic and clinical data of the participants, the painDETECT questionnaire was administered, followed by QST analysis to show the presence of hypoesthesia and/or hyperalgesia, and fMRI examinations, which included sensory stimulation of both extremities. Sensory threshold tests were found to be higher in the NP group compared with the healthy volunteers, and the heat pain threshold was found to be lower in the tests showing pain thresholds in the intergroup analyses (p < 0.05). The changes described were found in both painful and non-painful limbs. In the hypoesthetic NP group, a lower somatosensory cortex activity was found in non-painful limbs compared with the healthy volunteers (p < 0.05). In the unilateral hyperalgesic NP group, a lower somatosensory cortex activity was found on the painful side, and if the hyperalgesia was widespread, lower blood oxygen-level-dependent activity was also found in the operculum and insular cortex (p < 0.05). The patients with different phenotypes of NP had different activities in the areas related to the processing of pain, and were more prominent in patients with widespread hyperalgesia. Studies with larger numbers of patients are required for a definite statement.

Keywords: Cervical radiculopathy; Functional magnetic resonance imaging; Neuropathic pain; Quantitative sensory testing; Sensory phenotypes.