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

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.