Abstract
There are no reliable predictors of response to treatment with capsaicin. Given that capsaicin application causes heat sensation, differences in quantitative thermal testing (QTT) profiles may predict treatment response. The aim of this study was to determine whether different QTT profiles could predict treatment outcomes in patients with localized peripheral neuropathic pain (PeLNP). We obtained from medical records QTT results and treatment outcomes of 55 patients treated between 2010 and 2013. Warm sensation threshold (WST) and heat pain threshold (HPT) values were assessed at baseline at the treatment site and in the asymptomatic, contralateral area. Responders were defined as those who achieved a > 30% decrease in pain lasting > 30 days. Two distinct groups were identified based on differences in QTT profiles. Most patients (27/31; 87.1%) with a homogenous profile were nonresponders. By contrast, more than half of the patients (13/24, 54.2%) with a nonhomogenous profile were responders (p = 0.0028). A nonhomogenous QTT profile appears to be predictive of response to capsaicin. We hypothesize patients with a partial loss of cutaneous nerve fibers or receptors are more likely to respond. By contrast, when severe nerve damage or normal cutaneous sensations are present, the pain is likely due to central sensitization and thus not responsive to capsaicin. Prospective studies with larger patient samples are needed to confirm this hypothesis.
Highlights
Neuropathic pain is a chronic condition that is very difficult to treat [1], and only small improvements in treatment efficacy have been achieved in the last decade
We initially identified a total of 65 patients diagnosed with peripheral neuropathic pain (PeLNP) who had been treated with CP8% during the 2010–2013 period
There were no significant differences between the groups in terms of gender, age, Douleur Neuropathique 4 Scale (DN4), or pretreatment numerical pain rating scale (NPRS) scores
Summary
Neuropathic pain is a chronic condition that is very difficult to treat [1], and only small improvements in treatment efficacy have been achieved in the last decade. One of the most promising treatments for peripheral neuropathic pain (PeNP) developed in recent years is the capsaicin 8% patch (CP8%) (QutenzaTM). This patch delivers capsaicin into the skin and clinical trials have shown that it can provide up to 12 weeks of PeNP relief with a single topical patch application [2,3,4]. (TRPV1) receptor, which is primarily present in C-fibers and in some Aδ-fibers. High-concentration capsaicin activates TRPV1 channels by overstimulating the nociceptors, resulting in the defunctionalization of the nociceptor nerve fibers and thereby reducing spontaneous nerve activity, leading to a loss of responsiveness. Patients perceive a decrease in PeNP [5,6,7], which is frequently referred to as “desensitization.”
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