Essential tremor (ET) is a neurological disorder manifested by tremor (shaking) usually involving the hands, but may also affect the head, voice and other body parts. It is usually familial (genetic), but in some cases no family history of similar tremor is present. In contrast to rest tremor, which is typically present in patients with Parkinson’s disease and has a relatively slow frequency (3-5 Hz), ET is usually faster (4-10 Hz) and is most evident during activity such when writing, holding objects, or reaching out such as when eating. Many patients with ET experience a great deal of embarrassment when trying to sign checks, or when eating in public as they are unable to stand at parties and hold their plates filled with food, or they spill drinks when they bring cups or glasses to their mouth. ET is often worse during periods of psychological of physical stress. Alcohol, beta blockers (propranolol), primidone, topiramate, botulinum toxin injections and surgery (deep brain stimulation) are used to treat ET. Although the term “essential,” implies necessary or desirable, it actually means that there is no known cause and the term is synonymous with “idiopathic.” In the past, the modifier “benign” was used (“benign ET”) to indicate favorable prognosis of ET, even though it is now well accepted that ET can produce marked physical and psychosocial disability.
Some patients with ET also exhibit other movement disorders, such as dystonia. Dystonia is a neurological disorder manifested by repetitive or sustained (squeezing) contractions of muscles causing abnormal movements or postures. Examples of focal dystonia include blepharospasm, oromandibular (mouth and jaw) dystonia, cervical (neck) dystonia (torticollis), writer’s cramp, and other occupational cramps, such as musician’s dystonia. In children, dystonia typically starts as focal dystonia, such as writer’s cramp or foot inversion while walking or running, and then it spreads to involve the legs, trunk and the whole body. In adults, on the other hand, dystonia usually remains focal, and it rarely spreads beyond the initial body segment. Best examples of adult-onset dystonia are blepharospasm, oromandibular dystonia, cervical dystonia and cranial-cervical dystonia (sometimes still referred to as Meige’s syndrome).
About 25% of patients with cervical dystonia have tremor in their hands and arms similar to ET. This observation has sparked a debate about the relationship between dystonia and ET. Some clinicians have proposed that the hand/arm tremor in patients with cervical dystonia is another form of dystonia while others argue that ET and dystonia are two separate disorders that may co-exist in the same individual or the same family. We have, for example, published reports of families in which some members have only ET, others have only dystonia, and yet others have a combination of the two disorders. Until we discover a validated biologic or physiologic diagnostic marker for the two disorders, the controversy will probably continue.
Another form of tremor often associated with dystonia is the so-called “dystonic tremor.” This is a relatively slow and irregular tremor that occurs in the body part affected by the dystonia. Thus a patient with cervical dystonia manifested by involuntary turning of the head to one side (torticollis) may develop oscillation of the head when he or she attempts to keep the head in the straight position. Thus dystonic tremor occurs when a patient with dystonia tries to correct the abnormal posture. However, when the patient stops resisting the dystonic pulling, the dystonic tremor ceases (this position is referred to as “the null point”). Dystonic tremor may be alleviated or completely stopped with the use of certain maneuvers such as touching the chin or other “sensory tricks,” also called “geste antagonistique.” Similar to dystonia, dystonic tremor is best treated with local botulinum toxin injections, although muscle relaxants and other medications may also help. In severe cases, surgical treatment with deep brain stimulation may be necessary.