This is a strongly familial episodic tremor disorder of the chin and lower lip that begins in childhood and may worsen with age. Psychic stress and concentration are known to precipitate the movements, which are described by Danek as “trembling.” Rare instances involve other facial muscles. The disorder must be distinguished from a similar tremor of the chin that is part of essential tremor, facial myokymia or fasciculations, and palatal tremor. The disorder results from a mutation on chromosome 9.
This is a rare but striking tremor isolated to the legs that is remarkable by its occurrence only during quiet standing and its cessation almost immediately on walking. It is difficult to classify and more relevant to disorders of gait than it is to tremors of other types. The frequency of the tremor has been recorded as approximately 14 to 16 Hz, making it difficult to observe and more easily palpable. An important accompanying feature is the sensation of severe imbalance, which causes the patient to assume a widened stance while standing; these patients are unable to walk a straight line (tandem gait). We have observed prominent tonic contraction of the legs during standing, seemingly in an attempt to overcome imbalance (see Heilman; Thompson, Rothwell, Day et al). The arms are affected little or not at all. Often the first step or two when the patient begins to walk are halting, but thereafter, the gait is entirely normal. Because falls are infrequent, the symptoms are often attributed to hysteria. Tremulousness is not present when the patient is seated or reclining, but in the latter positions it can be evoked by strong contraction of the leg muscles against resistance.
Electromyographic recordings demonstrate rhythmic co-contraction of the gastrocnemius and anterior tibialis muscles. Although some authors, such as Wee and colleagues, have classified the disorder as a type of essential tremor, most of its characteristics suggest otherwise. Sharott and coworkers consider it an exaggerated physiologic tremor in response to imbalance; others have suggested a spinal origin for the tremor because of an intrinsic rhythm at approximately 16 Hz that is generated by damaged spinal cord in patients with myelopathy.
Some cases have responded to the administration of clonazepam, gabapentin, primidone, or sodium valproate alone or in combination but it often proves difficult to treat. A few intractable cases have been treated with an implanted spinal cord stimulator (Krauss et al, 2005).
Tremors may be a feature of incipient dystonia as mentioned earlier. When the underlying dystonic posturing is not overt, the tremor may be ascribed to the essential variety or to hysteria. Dystonic tremor is focal, for example superimposed on torticollis, or a dystonic hand. The movement is not entirely rhythmic, sometimes jerky, and often intermittent. These cases are also discussed further on in the section on focal dystonia. In addition, a fair number of patients with dystonia have an essential tremor.
Tremor may be a dramatic manifestation of hysteria. It simulates many types of organic tremor, often causing some difficulty in diagnosis. Psychogenic tremors are usually restricted to a single limb, often in the dominant hand; they are gross in nature and are less regular than the common static or action tremors. Importantly, they often diminish in amplitude or disappear if the patient is distracted as, for example, when asked to make a complex movement with the opposite hand. If the examiner restrains the affected hand and arm, the tremor may move to a more proximal part of the limb or to another part of the body (“chasing the tremor”). Other useful features in identifying hysterical tremor are paradoxical exaggeration of the tremor by loading the limb—for example, by having the patient hold a book or other heavy object—which reduces almost all other tremors with exception of those produced by polyneuropathy. Hysterical tremor often acquires the frequency of a willed movement in a different limb.
Tremors of Complex Type