Clinical Trial of the Safety and Efficacy of Peripheral Nerve Stimulation in the Treatment of Postherpetic Neuralgia.

The goal of this clinical trial is to evaluate safety and efficacy of percutaneous peripheral nerve stimulation in patients with postherpetic neuralgia. The main questions it aims to answer are:

1. The efficacy of percutaneous peripheral nerve stimulation in patients with postherpetic neuralgia
2. The safety of percutaneous peripheral nerve stimulation in patients with postherpetic neuralgia Participants are going to undergo procedure that implant peripheral nerve stimulation electrode produced by Jiangsu CED Medtech Co., Ltd. Then the subjects, whose VAS scores decrease more 30% than baseline level, are classified into two groups randomly. One of the group receiving active stimulation called trial group and another receiving placebo stimulation called control group. All subjects are required to make their own subjects' pain diary to record VSA score before and after implantation until at the end of follow-up. Also, participants are asked to report use of analgesic medications, number of awakenings and adverse events.

Researchers will compare pain scores between the two groups to see if peripheral nerve stimulation is effective to patients with postherpetic neuralgia.

The investigators divide study process into 3 main periods called enrollment/baseline period, treatment period and follow-up period. The treatment period is classified into test period, randomized withdrawal period and observation period further.

1. Enrollment/baseline period This study will be conducted at four clinical trial sites in China with 3 to 6 subjects included in the pretest and the formal trial planned to enroll 56 subjects. All subjects enter screening process after signing the informed consent form (ICF) approved by the ethics committee. Subjects are enrolled who meet inclusion criteria and do not meet any exclusion criteria. Enrolled subjects will undergo vital signs, physical examination, laboratory tests, and visual analogue scale (VAS) scores for pain for at least 4 days, Neuropathic Pain Scale (DN4), and the Short Form Health Survey (SF-36) as part of the screening period assessment prior to electrode implantation.
2. Treatment period 2.1 Implantation of devices Enrolled subjects are implanted with the percutaneous peripheral nerve stimulation system, which was parameterized by the investigator via a programmable controller. Subjects are provided with a "Transcutaneous Peripheral Nerve Stimulation Remote Control Instruction Manual" to guide them in the proper operation and use of the system.

   2.2 Test period Investigators will adjust stimulation parameters and record VAS score under different parameters conditions. The enrolled subjects are provided 1 to 5 stimulation therapy patterns parameterized by investigators after the test.

   Then the subjects receive continuous stimulation with parameterized patterns of 7 (±3) days and VAS scores are be recorded every day of 7 days. Subjects will enter next stage if their VAS scores decrease more than 30% from baseline level or withdraw the trial as reduction less than 30% and devices are removed.

   2.3 Randomized withdrawal period Subject will be classified into random group. One of the group receiving active stimulation called trial group and another receiving placebo stimulation called control group. Both of two groups are performed stimulation in the next 7 days. The subjects of control group will get active stimulation again as the VAS scores back to and maintain 2 days at baseline level. VAS scores will be recorded every day during this period.

   2.4 Observation period The devices are on work until 28th day after the implantation in trial group; stimulators are turned on after randomized withdrawal period until 28th day after the implantation in control group.

   All subjects have electrode leads removed on day 28 of implantation or at early withdrawal.
3. Follow-up period Investigators will begin follow up as the removal of electrode leads or on the day 28 of implantation. Indicators including VAS score will be evaluated and recorded to assess the efficacy and safety of percutaneous peripheral nerve stimulation during follow-up.

Eligibility Criteria:
Inclusion criteria:

* 18 years old and above, male or female
* Diagnosed by trained clinical doctors as postherpetic neuralgia, which is an indication for peripheral nerve stimulation therapy;
* Assess the damage or disease of the peripheral sensory system through the four questions of Douleur Neuropathy before surgery;
* The subject has received conventional treatment but the efficacy is poor, or cannot tolerate the side effects of conventional treatment;
* Visual analogue scale for pain within 24 hours before surgery ≥ 5;
* The subjects are able to understand the purpose of this study, have sufficient compliance with the research treatment, and are willing to sign an informed consent form;

Exclusion criteria:

* Subjects who need to receive both radio frequency modulation and intrathecal drug infusion treatment simultaneously;
* Subjects who are known to have cardiac implants (pacemakers or defibrillators) or other implantable neural stimulators (spinal cord stimulators or deep brain stimulators, etc.);
* Subjects with severe psychological and/or mental disorders and/or non therapeutic drug dependence;
* Subjects expected to undergo MRI examination within 30 days after PNS implantation;
* Expected to be discharged within 48 hours or less;
* Target nerve damage or muscle defects in known pain areas;
* Subjects who are known to be allergic to skin contact materials (tape or adhesive);
* Allergy to anesthetics such as lidocaine;
* Concomitant severe heart disease, liver disease, kidney disease, respiratory system disease, and coagulation dysfunction;
* Pregnant women, lactating women, or women planning to have children within the next three months;
* Subjects who have participated in any other clinical trial, or who may participate in any other trial after enrollment;
* Other situations that the researcher deems unsuitable for participation in this clinical trial