Michael T. Hayes, MD
Movement disorders is an area in neurology that deals not so much with strength or sensation, but more with complex movements such as walking or the ability to do a complex task like play the piano or write.
Movement disorders is a very prevalent group of diseases. There’s estimated to be half a million people in this country with dystonia, there’s estimated to be a million people in this country with Parkinson’s disease, and more if you consider all the other Parkinsonian diseases, and then there’s considered to be probably about 10 million patients with essential tremor.
The care of movement disorders is very individual. There are no two patients that are alike. Each patient has to be evaluated in an ongoing fashion to decide what is the appropriate treatment regimen; whether that involves injections, medications, or a surgical procedure that gives you the best effect for that individual patient.
Parkinson's disease occurs because there's a drop out of neurons in an area of the brain called the substantia nigra, which results in a loss of dopamine, a neurotransmitter. There are medications that increase the amount of dopamine in the brain or that stimulate dopamine receptors. These are a first line treatment. By stimulating dopamine receptors we can see an improvement in symptoms. Down the line, however, those medications may become ineffective or effective for a very short period of time during the day so that the patient has a very choppy and unpredictable day. At that point we think about other modalities.
There are surgical treatments. The most common one being used now is deep brain stimulation, in which an electrode is placed into a part of the brain that is the target for dopamine, allowing us to have some of the same effects of medication but on a more stable basis. The percentage of patients that might benefit from deep brain stimulation would probably be 15 percent.
MRI-directed implantation of deep brain stimulator electrodes allows the patient to be asleep during the entire procedure. Typically when deep brain stimulators are placed, the patient is awake. Because the brain has no pain receptors, you're able to do this but it does require the patient to be on a table, with their head locked into a frame, for a number of hours.
Doing the entire procedure under anesthesia allows the patient to be more comfortable. It also allows us to do direct anatomic evaluation of the electrode placement. We’ve found that that's very effective in terms of getting the electrode into the correct part of the brain so we're using that quite a bit.
Essential tremor is a form of degenerative disease. There's a loss of neurons. Where the loss of neurons occurs is not as well characterized as in diseases like Parkinson's disease. There's certainly some cases that have to do with loss of neurons in an area of the brain called the cerebellum, which is an area that helps people have smooth ramp movements, not choppy incoordinated movements. A loss of those neurons seems to result in essential tremor, but there are other parts of the brain that are suspected to be involved as well. It's not quite as well delineated as Parkinson’s disease.
There are a few medications for essential tremor that are effective in a subset of patients but it can be a very difficult disease to treat. It can be a very debilitating. When the medications don't work, again, there are standard types of surgical treatments, one of them again is deep brain stimulation but in a different part of the brain.
There are also newer therapies, such as focused ultrasound, that are being investigated as a less invasive way to improve a patient's tremors. The focused ultrasound procedure uses ultrasonic beams that intersect at the thalamus without creating an incision, without creating a burr hole, or without putting an electrode into the brain.
What happens with dystonia is, as the patient moves, there's motor overflow. The muscles become increasingly and increasingly tense and tightened to the point that the limb really doesn't function very well.
One of the treatments we use for dystonia is medication that results in some relaxation of the muscle. That can help patients by reducing the muscle tension.
We can also do more directed therapy by using botulinum toxin injections. Botulinum toxin forces the muscle to relax for about three months at a time. By doing very directed injections, often guided with EMG which allows us to actually record the muscle activity from the tip of the needle, we're able to sculpt the muscle to put the limb into the best position of function.
There are forms of dystonia that are treated with deep brain stimulation to a part of the brain called the globus pallidus interna. There's certainly a number of genetic forms of dystonia, but also acquired forms of dystonia, that benefit a lot from deep brain stimulation as well.
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