--that RSD, and other variants of complex regional pain syndrome, can mimic certain kinds of peripheral neuropathy, especially small-fiber varieties, and are therefore hard to distinguish diagnostically unless on is very, very painstaking.

Usually, trophic changes in the affected limb, such as skin reddening, are more characteristic of RsD:

http://neuromuscular.wustl.edu/sensory-pain.html#rsd

(Scroll up from where this takes you for more info on painful small-fiber syndromes.)

Sounds as if the doctor wants to perform a nerve conduction test--an NCV-- and will probably also conduct an electromyography (EMG). The former is to determine conduction in sensory nerves, the latter, in nerves that control muscles. These tests can be somewhat uncomfortable--a lot depends on the skill of the tester--in that small needles are inserted for the EMG and then your muscles are flexed, and during the NCV electric currents are passed through your skin, which can sting, but only momentarily; see WebMD's desciption of the testing:

http://www.webmd.com/brain/electromy...uction-studies


BTW, the "stickies" at the top of this forum are an excellent and comprehensive database for information about many kinds of neuropathy--take some leisurely time to go throught he links provided:

http://neurotalk.psychcentral.com/thread177.html