This study will evaluate patients with muscle stiffness for possible participation in current or future research studies. It will determine the cause of muscle stiffness or cramps and measure the severity of symptoms.

Children and adults with muscle stiffness, cramps or spasticity may be eligible for this study. Participants will provide a medical history and have a physical examination. In addition to the standard neurological examination, patients may be tested on how long it takes to make some movements, such as walking or tapping on a keyboard. To determine the cause of the muscle problem, patients may also undergo blood tests and the following procedures:

Magnetic resonance imaging (MRI) - MRI uses a strong magnetic field and radio waves to show structural and chemical changes in tissue. The patient lies on a table in a space enclosed by a metal cylinder (the scanner) for about 45 minutes, lying very still for 10 to 15 minutes at a time. The patient can communicate with the technician at all times during the procedure.

Electromyography (EMG) and nerve conduction studies - EMG measures the electrical activity of the muscles. A needle is inserted into a muscle to record its electrical activity. Nerve conduction studies measure the speed with which nerves conduct electrical impulses. A wire is taped on the skin over a nerve to deliver a small electrical stimulus and another wire taped to the skin records the impulses.

Patients will also be asked to fill out a health questionnaire no more than once a year. The information will be used to determine their eligibility for new studies.