Abstract
Introduction: Neuropathic pain associated with Non-freezing Cold Injury (NFCI) is a major burden to military service personnel. A key feature of NFCI is reduction of the intra-epidermal nerve fibre density in skin biopsies, in keeping with painful neuropathy. Current oral treatments are generally ineffective and have undesirable side effects. Capsaicin 8% patch (Qutenza) has been shown to be well-tolerated and effective for reducing neuropathic pain, for up to 3 months after a single 30-minute application.Methods: In this single-centre open label study, 16 military participants with NFCI (mean duration 49 months) received 30-minute Capsaicin 8% patch treatment to the feet and distal calf. Pain symptoms were assessed using a pain diary (with the 11-point Numerical Pain Rating Scale, NPRS) and questionnaires, the investigations included skin biopsies, performed before and three months after treatment.Results: Participants showed significant decrease in spontaneous pain (mean NPRS: −1.1, 95% CI: 0.37 to 1.90; p = 0.006), and cold-evoked pain (−1.2, 95% CI: 0.40 to 2.04; p = 0.006). The time-course of pain relief over 3 months was similar to other painful neuropathies. Patient Global Impression of Change showed improvement (p = 0.0001).Skin punch biopsies performed 3 months after the patch application showed significant increase of nerve fibres with structural marker PGP9.5 (intra-epidermal nerve fibres [IENFs], p < 0.0001; sub-epidermal nerve fibres [SENFs]; p =< 0.0001), and of regenerating nerve fibres with their selective marker GAP43 (p = 0.0001). The increase of IENFs correlated with reduction of spontaneous (p = 0.027) and cold-evoked pain (p = 0.019).Conclusions: Capsaicin 8% patch provides an exciting new prospect for treatment of NFCI, with regeneration and restoration of nerve fibres, for the first time, in addition to pain relief.
Highlights
Neuropathic pain associated with Non-freezing Cold Injury (NFCI) is a major burden to military service personnel
We have investigated the effect of Capsaicin 8% patch treatment in subjects with Non-freezing cold injury (NFCI) related painful neuropathy, as licenced (i.e. 3-monthly, if required)
Pain Scores and Questionnaires There was a significant reduction in the NUMERICAL PAIN RATING SCALE (NPRS) scores three months after Capsaicin 8% patch application for both spontaneous (Table 2, Figures 1A,B) and cold-evoked pain (Figures 1C,D)
Summary
Neuropathic pain associated with Non-freezing Cold Injury (NFCI) is a major burden to military service personnel. The condition termed Non-freezing cold injury (NFCI) was previously called Trench Foot, and it has been known since World Wars I and II to be a vaso-neuropathy [1,2,3]. NFCI and the associated chronic neuropathic pain are a particular burden to military personnel [3,4,5,6,7,8,9]. An underlying small fibre neuropathy and neuro-vascular changes have been demonstrated recently in skin biopsies, which may account for the chronic pain and persistent cold hypersensitivity [3]. Prescribed oral treatments for neuropathic pain generally have limited efficacy, with multiple side effects. NFCI may lead to a downgrading of functional status, and in many cases early discharge from the armed services
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