0.075% Capsaicin cream and wind up in chronic lumbar radicular neuropathic pain - a phenotype-stratified, case series

Abstract

Personalized treatment for low back pain disorders is a high research priority and stratified medicine using sensory profiling can potentially improve the outcomes. Wind-up, or temporal summation, is the progressive increase in action potential firing rate of spinal cord neurons to repetitive stimulation of C-fibre afferents at a constant intensity. Wind-up can occur in neuropathic pain, and it is augmented by the presence of central sensitization, which can lead to Aδ-fiber-induced wind-up rather than solely being activated by C-fibre stimuli. Topical capsaicin activates the transient receptor vanilloid1, which is expressed in C-fibres and some Aδ-fibers of the peripheral nervous system, leading to a reduction in skin evoked pain. Despite the supporting evidence for the 8% capsaicin patch, there is evidence that specific patient subgroups treated with 0.04% capsaicin formulation obtained better analgesia compared to the higher dose. However, that research did not evaluate sensory profiles nor predictive biomarkers. Due to the common neurophysiological pathways implicated in wind-up and capsaicin, our study posited that the adjunctive use of low-dose capsaicin cream (0.075%), coupled with physiotherapy, may offer analgesia in a subset of patients with chronic lumbar radicular neuropathic pain (n = 9, median pain duration of 5 years) who exhibit wind-up phenomena. The combination of topical capsaicin and physiotherapy yielded clinically significant analgesia (Hedges’ g = 2.96). Therefore, we propose investigating through a randomised controlled trials the utility of a simple bedside test as a predictive marker for a favourable response to 0.075% capsaicin cream in individuals with chronic lumbar radiculopathies who exhibit wind-up.