February 26, 2010
Dear Mayo Clinic:
I have been diagnosed as having orthostatic tremor and have come to realize that many people do not know how tremor can affect people. Please share with your readers about orthostatic tremor.
The term tremor implies an involuntary, rhythmic body movement. Orthostatic tremor affects the muscles in a person's legs, and sometimes also radiates from the legs upward to other parts of the body. The term "orthostatic" refers to standing. Orthostatic tremor occurs when a person stands up. The condition can be difficult to diagnose and, although medication helps some people, it can be a challenging condition to treat effectively.
Orthostatic tremor is an uncommon disorder that can significantly affect the quality of life for those who develop it. Usually, the main symptom is a feeling of leg shakiness and unsteadiness when standing still. Orthostatic tremor can create difficulty in performing daily activities that require a person to stand freely without support. For example, standing in line at a store, standing at a kitchen counter to prepare a meal, or standing at a workbench to enjoy a hobby can be very hard or impossible for people who have orthostatic tremor. Most people don't fall as a result of the condition. However, approximately 15 percent become so unsteady that falling is a problem.
Orthostatic tremor often starts shortly after standing and stops when a person sits or lies down. Contrary to what common sense might normally suggest, typically the tremor decreases when a person is walking. Leaning on an object such as a chair or a countertop when standing also may help reduce the tremor.
Orthostatic tremor is a high-frequency tremor, which means the tremor rhythm is very rapid and there can be as many as 16 to 20 tremor cycles in one second. That's significantly faster than other tremor types. For example, essential tremor usually involves eight to 12 tremor cycles per second, and the tremors associated with Parkinson's disease typically occur at a rate of four to eight cycles per second.
Because the tremor is so fast, orthostatic tremor can be difficult to see. That can make the diagnosis challenging. In some cases, when patients report that they feel unsteady on their feet, the physicians may overlook the leg tremor and may pursue other possible causes of unsteadiness. One additional diagnostic strategy is to place a hand on the thigh, feeling for the tremor; however, the clinician must have an appropriate level of suspicion.
If a physician suspects orthostatic tremor, the diagnosis can be confirmed by assessing the electrical activity in the leg muscles. At Mayo Clinic, that analysis is conducted in our Movement Disorders Neurophysiology Laboratory. During orthostatic tremor, the leg muscles show no electrical activity when a person is sitting. When he or she stands up, though, the muscles immediately begin firing rhythmic bursts of electrical activity.
Because the cause of orthostatic tremor is unknown, a cure currently isn't available. Instead, treatment focuses on the symptoms. Once the condition is diagnosed, the first line of treatment is the medication clonazepam or a related drug. This medication moderately to markedly reduces orthostatic tremor in about one-third of people who have the disorder. For some, it eliminates orthostatic tremor almost entirely.
Unfortunately, for those who don't respond to clonazepam, no single alternative medication has a high likelihood of decreasing orthostatic tremor. Although numerous other medications may be tried, these may be no more than mildly helpful.
Fortunately, orthostatic tremor tends not to be a progressive disorder. Once the symptoms are fully developed, it doesn't progress to a more pervasive neurological condition. It does tend to be persistent, however, and usually does not resolve on its own.
ā J. Eric Ahlskog, M.D., Ph.D., Neurology, Mayo Clinic, Rochester, Minn.