Study of Possible Changes in QST After Application of Capsaicin on Patients With Peripheral Neuropathic Pain

Study Overview
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Brief Summary
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The treatment of neuropathic pain ist still a challenge. A new promising therapy is the use of capsaicin on skin. The investigators first experiences with capsaicin in patients with peripheral nerve injury showed changes in the sensibility, which achieved its maximal extent after four weeks and was regressive, but not completely abolished 1,5 months after application. In this study the investigators hope to specify, how long and in which way exactly this changes in sensibility appear.

Detailed Description
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The topical application of a high dosage of capsaicin (8%) is a new promising approach. There is only little knowledge about the extent and the duration of drug-induced changes of detection and pain thresholds based on a currently recommended standardized quantitative sensory testing (QST). The assessment of QST changes would be an important step forward to understand the way of action as well as the time course of the presumed recovering of the C-fiber function after topical application of a high concentration capsaicin patch. 10 patients suffering from peripheral neuropathic pain due to peripheral nerve injury and 10 patients suffering from postherpetic neuralgia will be investigated by QST following the protocol of DFNS (German Research Network on Neuropathic Pain), using both thermal and mechanical nociceptive as well as non-nociceptive stimuli. QST will be performed at the following times: at baseline 2, 4, 6, 8 weeks later, and every two weeks at least until re-occurrence of pain and/or recovering of the capsaicin-induced worsening of the C-fiber function.

Official Title
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Kind and Duration of Possible Changes of the Sensory Profiles After the Topical Application of Capsaicin (8%) in Patients With Peripheral Neuropathic Pain

Conditions
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Peripheral Nerve Injury, Postherpetic Neuralgia

Intervention / Treatment
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* Procedure: quantitative sensory testing (QST)


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: age >18 years with signed informed consent with planned topical application of capsaicin (8%) and with no involvement in any other study with neurological proved peripheral neuropathy (e.g. peripheral nerve lesion, postherpetic neuralgia) and with remaining moderate pain intensity under the current treatment (> NRS 3; numeric rating scale 0-10) some remaining sensory function at the baseline QST with z-scores ≥ - 3 for cold, warmth and tactile thresholds Exclusion Criteria: with missing informed consent with any contraindications for capsaicin application with diabetes mellitus, using lidocaine patch in the test area in the last 6 months before enrollment with inadequate knowledge of the german language

Ages Eligible for Study
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Minimum Age: 18 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| patients with peripheral nerve injury<br>10 patients with neuropathic pain, because of peripheral nerve injury will obtain a baseline-QST and after capsaicin-application a QST 2, 4, 6, 8 and every 2 weeks until re-occurrence of pain and/or recovery of the capsaicin-induced sensory deficits | Procedure: quantitative sensory testing (QST)<br>* with QST the small-fibre function is tested by registering thermal and mechanical thresholds, so that changes in the sensory profile can by specified<br>|
| patients with postherpetic neuralgia<br>10 patients with neuropathic pain, because of postherpetic neuralgia will obtain a baseline-QST and after capsaicin-application a QST 2, 4, 6, 8 and every 2 weeks until re-occurrence of pain and/or recovery of the capsaicin-induced sensory deficits | Procedure: quantitative sensory testing (QST)<br>* with QST the small-fibre function is tested by registering thermal and mechanical thresholds, so that changes in the sensory profile can by specified<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Duration of the functional loss of the C- and A-delta-fibres after therapeutic application of capsaicin 8% as measured by the impairment of the thermal thresholds | measurement of thermal detection thresholds for warmth (WDT) and cold (CDT) by QST (standard DFNS protocol), change of z-values for WDT and CDT from baseline to 8 weeks after capsaicin-application (ANOVA) | 8 weeks after capsaicin-patch (8%) application | 
| Extent of the functional loss of the C- and A-delta-fibres after therapeutic application of capsaicin 8% as measured by the impairment of the thermal thresholds | measurement of thermal detection thresholds for warmth (WDT) and cold (CDT) by QST (standard DFNS protocol), change of z-values for WDT and CDT from baseline to 8 weeks after capsaicin-application (ANOVA) | 8 weeks after capsaicin-patch (8%) application | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Decrease of thermal Hyperalgesia | change of thermal hyperalgesia measured by QST (z-value of heat pain and cold pain threshold)from baseline to 8 weeks after capsaicin-application | 8 weeks after capsaicin-patch (8%) application | 
| Decrease of mechanical hyperalgesia | change of mechanical hyperalgesia measured by QST (z-value of mechanical pain threshold and mechanical pain sensitivity) from baseline to 8 weeks after capsaicin-application | 8 weeks after capsaicin-patch (8%) application | 
| Decrease of dynamical mechanical allodynia | change of dynamical mechanical allodynia measured by QST from baseline to 8 weeks after capsaicin-application | 8 weeks after capsaicin-patch (8%) application | 
| Correlation of efficacy on the sensory function and the reported soothing of symptoms after capsaicin-application | comparison of z-values for cold, warmth and mechanical detection threshold to the outcome of the german versions of the following questionnaires: PainDETECT, NPSI (Neuropathic Pain Symptom Inventory) and Patient's global impression of change (PGIC), analyzed by ANCOVA | 8 weeks after application of capsaicin-patch (8%) | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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peripheral nerve injury, postherpetic neuralgia, PNI, PHN, Capsaicin, QST, quantitative sensory testing, sensory profile, neuropathic pain