Movement Disorders Laboratory: Diagnosing and treating complex dystonias
Movement disorders such as tremor, dystonia and Parkinson's disease are among the most common neurological conditions. For patients, movement disorders can result in considerable disability. Hand and arm tremors can impair eating, handwriting and grooming. Vocal tremor can hinder communication, resulting in social withdrawal. For the physician, precise diagnosis can be difficult because of the broad array of related movement disorders.
The Mayo Clinic Movement Disorders Laboratory in Rochester, Minn., is one of the few centers in the United States that offers a wide range of analytic techniques capable of aiding in the classification of these conditions. Among the techniques used are:
- Tremor frequency analysis
- Quantitative brain wave analysis
- Dystonia mapping studies
- Movement pattern analysis
The core assessment tool comprises simultaneous EEG, EMG and video recordings taken while the patient exhibits abnormal movements.
"Most EMG laboratories focus on disorders of the peripheral nervous system. But our laboratory also uses these techniques to diagnose problems of the central nervous system," explains Joseph Y. Matsumoto, M.D., a neurologist in Mayo's Movement Disorders Subspecialty Group and the director of the Movement Disorders Laboratory.
A typical diagnostic test lasts 20 to 45 minutes in the Movement Disorders Laboratory. Surface EMG is used to monitor muscle activity. For some conditions, such as myoclonus, EEG helps to determine the locus of abnormal movement in the CNS. Computer analysis of the recordings has advantages for diagnostic specificity. "For example, we can generally identify the precise type of tremor a patient has," Dr. Matsumoto says.
Rare movement disorders
The experience and expertise of Mayo's movement specialists extend to rare movement disorders, such as orthostatic tremor and stiff man syndrome (SMS), also known as stiff person syndrome. (Women made up two-thirds of patients who received a diagnosis of this rare disorder at Mayo over the period from 1984 through December 2008.)
SMS, identified by Mayo Clinic doctors in 1956, is characterized by chronic rigidity and spasms in the muscles of the limbs and trunk. Patients frequently have painful spasms and falls, as well as fixed spinal deformities from long-term rigidity. Some patients have respiratory impairment from chest wall spasms.
SMS is distinguishable by hyperexcitability of spinal motor neurons. Mayo's Movement Disorders Laboratory uses multichannel surface EMG, concentric needle studies of the lumbar paraspinal muscles, and electrical and acoustic stimulation of the nerves to evaluate startle reflexes in suspected cases of SMS. "SMS is often mistaken for a psychogenic disorder," Dr. Matsumoto says. "But electrophysiological findings consistent with brainstem and spinal hyperexcitability can help confirm the clinical suspicion in many cases."
Diagnostic testing in the Movement Disorders Laboratory can also guide treatment. For example, multichannel EMG needle mapping studies can pinpoint areas of activity that cause spasmodic torticollis. Precise localization can then help physicians choose sites for injecting botulinum toxin and can identify patients who might benefit from surgical treatment.
Mayo also has a large practice in treating spasmodic dysphonia and jaw and orofacial dystonias with botulinum toxin. Movement disorders neurologists, ear-nose-throat surgeons and speech pathologists share a close collaboration in caring for patients who receive these complex injections.
"Movement disorders, particularly in rare conditions, can be very difficult to diagnose and treat," Dr. Matsumoto notes. "Our lab's expertise lies in clarifying a difficult diagnosis, as well as providing botulinum toxin treatment in common and rare conditions."