Dystonia is generally regarded as a motor execution abnormality due to a central nervous system dysfunction in the cortico-striato-thalamo-cortical motor loop. Regional traumas are considered to be risk factors for the development of focal dystonia (FD) in the affected limb. Since focal limb traumas are also associated with complex regional pain syndrome (CRPS), there may be a common underlying pathology in both conditions. In CRPS, many patients have a small fiber neuropathy. The goal of the proposed research is to distinguish (discriminate) among the three disease categories (FD, FD+CRPS, CRPS), to find out whether FD and CRPS share a common physiological substrate and represent two sides of a spectrum, and to see which clinical situations may be secondary to an underlying small fiber neuropathy. Independent studies will be conducted in patients with affected upper limbs and in those with affected lower limbs.