Carpal tunnel syndrome (CTS) is the most common peripheral entrapment neuropathy with involving compression of the median nerve in the carpal tunnel. Rather than other progressive disease, CTS is characterized by remission and recurrence. Although many conservative managements of CTS, the effectiveness of these methods is insignificant or only persist for a short duration. The platelet rich plasma (PRP) is a new and potential treatment for patients with kinds of musculoskeletal disorders and recent reports showed being beneficial for peripheral neuropathy in animal studies. Since 2014, two small clinical trials showed the positive effect of PRP in peripheral neuropathy. One study shown the PRP has therapeutic effect for peripheral neuropathy in patients with leprosy. In addition, PRP having protective effect against neurological deficit of facial nerve during superficial parotidectomy. However, these studies have not entirely proved the effects of PRP on peripheral neuropathy because these studies enrolled small number of patients and lacked controlled design. In addition, the PRP was not used for treating CTS so far. The investigators design a randomized, double-blind, controlled trail to assess the effect after ultrasound-guided PRP injection in patients with CTS.