The Association Between Focal Dystonia (FD) and Complex Regional Pain Syndrome (CRPS)

This study will investigate differences among people with focal dystonia (FD), complex regional pain syndrome (CRPS) and people who have both conditions to learn more about the cause of both disorders.

Participants undergo the following procedures in five visits:

• Electroencephalography (EEG). Electrodes (metal discs) are placed on the scalp with an electrode cap, a paste or a glue-like substance. The spaces between the electrodes and the scalp are filled with a gel that conducts electrical activity. Brain waves are recorded while the subject lies quietly and sensory stimulation is applied to the thumb or finger.
• Magnetic resonance imaging (MRI). This test uses a magnetic field and radio waves to obtain images of body tissues and organs. The patient lies on a table that can slide in and out of the scanner, wearing earplugs to muffle loud knocking and thumping sounds that occur during the scanning process. The procedure lasts about 45 minutes, during which time the patient will be asked to lie still for up to 15 minutes at a time.
• Transcranial magnetic stimulation (TMS). An insulated wire coil is placed on the scalp and a brief electrical current is passed through the coil. The current induces a magnetic field that stimulates the brain. There may be a pulling sensation on the skin under the coil and a twitch in muscles of the face, arm or leg. During the stimulation, subjects may be asked to keep their hands relaxed or to contract certain muscles.
• Peripheral electrical stimulation. In two experiments, TMS is combined with peripheral electrical stimulation, similar to what is used in nerve conduction studies, to the median nerve at the wrist. There may be muscle twitching.
• Surface electromyography. For TMS tests and peripheral electrical stimulation, electrodes are filled with a conductive gel and taped to the skin to record the electrical activity of three muscles on the right hand.
• Needle EMG. A needle is inserted into a muscle to record the electrical activity.
• Nerve conduction studies. A probe is placed on the skin to deliver a small electrical stimulus, and wires are taped to the skin record the nerve impulses. These studies measure the speed with which nerves conduct electrical impulses and the strength of the connection between the nerve and the muscles.
• Skin biopsy. Two sites are biopsied. A local anesthetic is given to numb the area and a 1/4-inch piece of skin is removed with a special tool.
• JVP domes. Subjects are tested for their ability to discriminate sensory stimuli in the affected region and on the other side of it. They are asked to discriminate between stamps with grooves of different widths that are applied to the hands or feet.