Figure 1
Tremor generation by an oscillating circuit. An oscillation may arise whenever there is a delay in a negative feedback loop or an increase in gain in the control signal. A reference signal provides input about the target or goal state; a comparator compares the sensed information and the reference signal; gain transforms comparison into a control signal (i) that brings the sensed position closer to the reference signal, thus negating the error; the plant converts control signals into real output.
Table 1
Common Tremor Disorders Classified According to Two Main Criteria
| Relation to Voluntary Movement | Relation to Body Part |
|---|---|
| Rest tremor | Head tremor |
| Parkinson disease | Cerebellar disease |
| Other parkinsonian syndromes | Dystonia |
| Tardive (drug-induced) parkinsonism | Essential tremor (rarely when isolated) |
| Vascular parkinsonism | Chin tremor |
| Hydrocephalus | Parkinson disease |
| Psychogenic (functional) tremor | Hereditary geniospasm |
| Action tremor | Jaw tremor |
| Postural tremor | Parkinson disease |
| Physiologic tremor and enhanced physiologic tremor | Dystonia |
| Essential tremor | Palatal tremor |
| Dystonic tremor | Idiopathic (essential) |
| Parkinsonism | Owing to brainstem lesions (secondary) |
| Fragile X premutation (fragile X tremor–ataxia syndrome) | Owing to degenerative disease (adult-onset Alexander disease) |
| Neuropathies | Arm tremor |
| Tardive tremor | Cerebellar disease |
| Toxins (e.g., mercury) | Distonia |
| Metabolic disorder (e.g., hyperthyroidism, hypoglycemia) | Essential tremor |
| Psychogenic (functional) tremor | Parkinson disease |
| Kinetic tremor | Leg tremor |
| Cerebellar disease | Parkinson disease |
| Holmes tremor | Orthostatic tremor |
| Wilson disease | |
| Psychogenic (functional) tremor |
Table 2
Clinical Criteria for the Physical Signs Observed in Patients with Dystonia
| Physical Sign | Description |
|---|---|
| Dystonic postures | Muscle contractions may be continuous, forcing limbs and trunk into sustained postures (not available for blepharospasm or laryngeal dystonia) |
| A body part is flexed or twisted along its longitudinal axis | |
| Slowness and clumsiness for skilled movements are associated with sensation of rigidity and traction in the affected part | |
| Dystonic movements | These features have to be looked for in all movement disorders, either fast or slow, also when the immediate impression is that of a tremor, tic, chorea, or myoclonus |
| Tremor is a feature of dystonic movements and may appear as isolated tremor | |
| Movements are repetitive and patterned (i.e., consistent and predictable) or twisting | |
| Movements are often sustained at their peak to lessen gradually in a preferred posture (usually opposite to the direction of movement) | |
| Gestes antagonistes (“sensory tricks”) | Are voluntary actions performed by patients that reduce or abolish the abnormal posture or the dystonic movements? |
| They are usually simple movements involving, or directed to, the body region affected by dystonia | |
| These movements are natural and graceful, not consisting in forceful opposition to the phenomenology of dystonia | |
| The movement does not push or pull the affected body part, but simply touches it (“sensory trick”) or accompanies it during alleviation of dystonia | |
| Alleviation of dystonia occurs during the geste movement, usually soon after its start | |
| Alleviation may last for as long as the geste or slowly reverses spontaneously before its end | |
| Mirror dystonia | It is evaluated in the upper or lower limbs. At least three different types of repetitive tasks (e.g., finger sequence, normal writing, or piano-like movements) are performed at low and fast speed in the non-affected limb |
| It is a unilateral posture or movement with same or similar characteristics to the patient’s dystonia (usually postures and some movements) that can be elicited, usually in the more severely affected side, when contralateral movements or actions are performed | |
| Overflow dystonia | It is observed at least once, usually ipsilaterally, in coincidence with the peak of dystonic movements |
| It is an unintentional muscle contraction accompanying the most prominent dystonic movement, but in an anatomically distinct neighboring body region |
Table 3
Features Considered Typical of the Essential Tremor Syndrome
| Feature | Description |
|---|---|
| Tremor | 4–12 Hz action tremor that occurs when patients voluntarily attempt to maintain a steady posture against gravity (postural tremor) or move (kinetic tremor) |
| Tremor may be suppressed by performing skilled manual tasks | |
| Tremor resolves when the body part relaxes as well as during sleep | |
| Tremor at rest is not uncommon and observed in approximately 20% of patients | |
| Age at onset | Adolescence (15–20 years) or late adulthood (50–70 years) |
| Distribution | Bilateral with minimal asymmetry |
| Affected body sites1 | Upper limbs >> head >> voice >> face/jaw >> tongue >> trunk >> lower limbs |
| Progression | Tremor may initially be intermittent, occurring during periods of emotional activation, and then becomes persistent over time |
| Response to alcohol | Beneficial alcohol response present in 50–75% of patients |
| Family history | Positive family history present in 30–60% of patients |