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Presence of hyperalgesia predicts analgesic efficacy of topically applied capsaicin 8% in patients with peripheral neuropathic pain
Author(s) -
Mainka T.,
Malewicz N.M.,
Baron R.,
EnaxKrumova E.K.,
Treede R.D.,
Maier C.
Publication year - 2016
Publication title -
european journal of pain
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.305
H-Index - 109
eISSN - 1532-2149
pISSN - 1090-3801
DOI - 10.1002/ejp.703
Subject(s) - capsaicin , neuropathic pain , hyperalgesia , medicine , anesthesia , postherpetic neuralgia , peripheral , threshold of pain , analgesic , nociception , neuralgia , receptor
Background Topical high‐dose capsaicin acting on TRPV 1 receptors and inducing an intraepidermal decrease in the small nerve fibre count is effective in treating neuropathic pain ( NP ). Sensory changes after capsaicin application, their correlation with pain relief and their role as possible predictors of response have been insufficiently analysed. We hypothesized a positive correlation between pain relief and increase in the warmth detection threshold ( WDT ), indicating loss of C‐fibre function, and higher response rates in patients with preserved C‐fibre function or heat hyperalgesia before application. Methods Quantitative Sensory Testing ( DFNS protocol) was conducted in 20 unilaterally treated patients with peripheral NP (peripheral nerve injury: n = 14, polyneuropathy: n = 4, postherpetic neuralgia: n = 2) before and 2, 4, 6 and 8 weeks after application of capsaicin (8%) in this open‐label study. Response was defined as ≥30% or ≥2 (Numeric Rating Scale: 0–10) decrease of current pain at any follow‐up compared to baseline. Results In all patients, WDT significantly increased 8 weeks after capsaicin application, but did not correlate with pain relief in responders ( n = 10, r = 0.179, p = 0.141). Before treatment, responders showed significantly higher z ‐values for the cold ( CPT , +0.7 ± 1.1 vs. −0.4 ± 0.9) and mechanical pain threshold ( MPT ; 0.7 ± 2.5 vs. −1.2 ± 1.3), but did not differ from non‐responders regarding WDT or heat pain threshold. A sum of the z‐values for CPT and MPT >0.8 before treatment identified responders with 100% specificity and 70% sensitivity. Conclusions Efficacy of capsaicin does not correlate with the induced loss of function of small fibres, measured by QST . Presence of cold and pinprick hyperalgesia seems to be predictive of response to capsaicin (8%).