Augmented Cerebral Activation by Lumbar Mechanical Stimulus in Chronic Low Back Pain Patients

Abstract

Cerebral activation by lumbar mechanical stimulus was investigated by functional magnetic resonance imaging in healthy subjects and patients with chronic low back pain (LBP). To characterize the cerebral substrates of LBP, and to explore a possible pathologic pattern of cerebral activation in chronic LBP patients. The cerebral substrates of LBP have been poorly defined in contrast to those of cutaneous somatic pain. Eight healthy volunteers and 6 patients with idiopathic, chronic LBP were recruited. Each subject was placed in the prone position on a 3 Tesla MRI scanner, and stimulated by manual pressure with the tail of an air-filled, 20-mL syringe at 5 cm left of the fourth-fifth lumbar spinal interspace. Three blocks of 30-second painful stimulus, calibrated at either 3 or 5 on the 10-cm visual analog scale (VAS), were applied with intervening 30-second rest conditions during whole-brain echo-planar imaging. VAS of pain intensity and unpleasantness were evaluated after each session. Functional imaging was analyzed using a multisubject general linear model with Bonferroni multiple comparisons at P < 0.05. Pain thresholds were smaller (P < 0.05) and VAS of unpleasantness was larger in LBP patients than in healthy subjects. Activation was observed at the prefrontal, insular, posterior cingulate cortices (PCC), supplementary motor, and premotor areas predominantly in the right hemisphere, but not at the somatosensory cortices. LBP patients showed augmented activation compared with healthy volunteers specifically at the right insula, supplementary motor, and PCC. Chronic LBP patients showed increased tenderness at the lower back, higher aversive reaction to pain, and augmented LBP-related cerebral activation. The LBP-related activation is characterized by the absence of sensory-discriminative component and the involvement of PCC.