A prospective open label pilot study to investigate whether quantitative sensory testing correlates with the effectiveness of diagnostic dorsal root ganglion block in patients with unilateral lumbar radiculopathy

Abstract

Lumbar radicular pain is defined as neuropathic pain in the area supplied by the affected nerve root, which may be treated by targeting the dorsal root ganglion (DRG). Central sensitization can occur following peripheral nerve injury, via autosensitization of nociceptive receptors and ectopic firing of DRG cells.1 We hypothesize that central nociceptive processing may be modulated by DRG blockade with local anaesthetic and steroid. This study used quantitative sensory testing (QST) to investigate changes in peripheral and central sensitization in patients undergoing therapeutic DRG block for radicular low back pain. Fifteen patients were recruited for the study, after approval of the local research ethics committee, to undergo DRG blockade with local anaesthetic and steroid (inclusion criteria: unilateral lumbar radicular pain with concordant disc herniation confined to the spinal canal on magnetic resonance imaging). This was performed by a single operator with fluoroscopic guidance, using 1ml 0.25% bupivacaine and 20mg methylprednisolone per level. QST measurements were taken one week before and after their procedure; mechanical pressure pain threshold (PPT) was measured using manual pressure algometry, and diffuse noxious inhibitory control (DNIC) was measured by recording changes in PPT in response to experimental arm pain. A visual analogue scale (VAS) was used to measure pain intensity. There was a significant increase in PPT after DRG blockade (painful side p<0.0005 versus non-painful side p<0.004). A diminished DNIC response was seen prior to DRG blockade, increasing after the procedure (p<0.0001); this suggests ‘normalisation’ of pressure pain modulation. Pain intensity scores improved after DRG blockade (7.45 +/- 1.9 versus 2.28 +/- 0.26). This pilot data indicates that DRG blockade with local anaesthetic and steroid may have effects on peripheral and central sensitization. Potential mechanisms include modulation of afferent fibre nociceptive input on central nociceptive processing. (1. Schwartzman RJ, Arch Neurol, 2001.)