We use our hands constantly. Every morning millions of people shower, shave, get dressed, eat breakfast — tasks that would be incredibly difficult without steady hands. For an estimated 10 million Americans with a neurological disorder called essential tremor, shaking of their arms and other body parts makes it difficult or even impossible to perform the simplest of movements.
The condition, which affects the muscles of the hands, head, and voice, is often mistaken for Parkinson's patients. But essential tremor is 5-10 times more common than Parkinson's disease. Most people diagnosed with essential tremor have action tremor, which means they shake when they move, and some develop a distinctive nodding or shaking of the head. People with Parkinson's usually experience tremors at rest, along with stiffness and slowness of movement.
But there's some overlap between the two conditions. Some studies show that 90% of Parkinson's patients have action tremor and 20% of people with essential tremor have tremor at rest. Both conditions cause a loss of the sense of smell, but in essential tremor it's usually milder. Patients with essential tremor can go on to develop Parkinson's disease, but how many do so isn't known.
Katherine Hepburn had essential tremor. Medical historians believe the playwright Eugene O'Neill and the American revolutionary Samuel Adams may have also had the disease. Researchers have diagnosed Adams by analyzing the handwriting in his letters.
Medical texts from ancient India and Greece mention tremors. Charles Dana, the famous 19th-century neurologist, wrote detailed case histories of people with tremors. Despite this long history, essential tremor isn't fully understood. Most experts believe that it's caused by the death or malfunction of brain cells in the cerebellum, the part of the brain that controls movement and balance. But in contrast to Parkinson's, characterized by a shortage of dopamine, a brain chemical involved in movement, essential tremor doesn't seem to involve any neurotransmitter abnormalities.
Essential tremor runs in families; in fact, it's sometimes referred to as familial tremor. But studies of identical twins have shown that it's not completely inherited, suggesting an environmental factor may trigger some cases, although what that might be is unknown.
Misdiagnosis of essential tremor is a problem. Doctors don't have a definitive test, so some people are given Parkinson's medication when they shouldn't be. The first steps in making the diagnosis are taking a family history and ruling out other causes of tremors, which include excessive caffeine, stress, fatigue, anxiety, and hyperthyroidism. There are also some less common neurological disorders that cause shaking, including dystonia and Wilson's disease.
Many people with essential tremor discover, sometimes inadvertently, that alcohol eases the shaking. As a result, some people with the condition end up drinking too much.
Beta blockers — especially a long-acting version of propranolol (Inderal) — are one of two main medications used to treat essential tremor. Adrenaline makes tremors worse, and beta blockers, which are usually prescribed for high blood pressure and heart conditions, block adrenaline. (The term "beta blocker" is shorthand for beta-adrenergic blocker; "adrenergic" refers to compounds like adrenaline.) Studies show that beta blockers help 45%-75% of patients.
The other main drug is primidone (Mysoline), an anticonvulsant. Anticonvulsants work by reducing the excitability of nerve cells. Primidone is about as effective as propranolol, but it can cause nausea, vomiting, and ataxia (problems with movement). Studies of another anticonvulsant, topiramate (Topamax), are promising, but a high proportion of patients experience side effects. Many sufferers eventually need to take propranolol (the beta blocker) and primidone together to get adequate relief, leading some researchers to think the condition has multiple causes.
Surgery is an option for people with severe tremors, but operating on the brain obviously carries risk. Thalamotomy, introduced in the 1950s to help Parkinson's patients, destroys part of the thalamus, a region of the brain involved in involuntary muscle movement. It's a fairly effective operation, but possible side effects include difficulty swallowing or talking and an increased risk of stroke.
Deep brain stimulation is another procedure. It involves placing electrodes in the brain that are connected to a pacemaker-like device implanted in the patient's chest. The device sends small electric impulses through the electrode. The impulses interrupt the communication between cells involved in tremors.
December 2004 Update