A common cause of neuropathy is diabetes, but in about 25 to 50% of the population no cause is found. This group is often referred to as cryptogenic sensory polyneuropathy (CSPN). This study looks at four different drugs in patients with CSPN and plan to determine which drug is most effective: nortriptyline, duloxetine, pregabalin, or mexiletine. The study is funded through PCORI: Patient-Centered Outcomes Research Institute whose research is “designed to improve patient care and outcomes through patient-centered comparative clinical effectiveness research.” Click here for locations.