Patients are randomized to receive amitriptyline, mexiletine, or benztropine mesylate as an active placebo to mimic the mild side effects associated with both amitriptyline and mexiletine. Doses are gradually increased over 4 weeks until a minimum effective dose or MTD is reached, then patients are treated for at least 4 additional weeks at the final dose before gradually tapering off. Neurologic exams are performed at screening and at the end of treatment. Intensity of pain is rated twice daily by the patient. Patients are followed at Weeks 2, 4, and 8, and at 10 days after completely tapering off of drug.