This is a proposal of the Movement Disorder Society for a clinical classification of tremors. The classification is based on the distinction between rest, postural, simple kinetic, and intention tremor (tremor during target-directed movements). Additional data from a medical history and the results of a neurologic examination can be combined into one of the following clinical syndromes defined in this statement: enhanced physiologic tremor, classical essential tremor (ET), primary orthostatic tremor, task- and position-specific tremors, dystonic tremor, tremor in Parkinson's disease (PD), cerebellar tremor, Holmes' tremor, palatal tremor, drug-induced and toxic tremor, tremor in peripheral neuropathies, or psychogenic tremor. Conditions such as asterixis, epilepsia partialis continua, clonus, and rhythmic myoclonus can be misinterpreted as tremor. The features distinguishing these conditions from tremor are described. Controversial issues are outlined in a comment section for each item and thus reflect the open questions that at present cannot be answered on a scientific basis. We hope that this statement provides a basis for better communication among clinicians working in the field and stimulates tremor research.

Consensus statement of the Movement Disorder Society on tremor

The sections in this article are:


1
Neural Control of Postural Orientation and Equilibrium
1.1
Behavioral Goals

1.2
Biomechanical Principles

1.3
Postural Strategies




2
Postural Orientation
2.1
Stiffness and Tonic Muscle Activation

2.2
Controlling Postural Orientation

2.3
Internal Representation of Postural Orientation




3
Coordination of Postural Equilibrium
3.1
Triggered Reactions to External Disturbances

3.2
Anticipatory Postural Adjustments for Voluntary Movement

3.3
Modeling of Postural Coordination




4
Sensory Control of Postural Orientation and Equilibrium
4.1
Sensory Integration

4.2
Somatosensory System

4.3
Vestibular System

4.4
Visual System




5
Central Neural Control of Posture
5.1
Spinal Cord and Brainstem

5.2
Basal Ganglia

5.3
Cerebellum

5.4
Cerebral Cortex




6
Concluding Remarks

Postural Orientation and Equilibrium

Primary chronic daily headache can be subdivided into transformed migraine, chronic tension-type headache, hemicrania continua, and new daily persistent headache. We proposed and tested criteria in 150 consecutive outpatients with chronic daily headache. Based on preliminary analysis, we revised the criteria for transformed migraine. Using the International Headache Society criteria, 43% of the patients could not be classified; using our old criteria, 25% could not be classified; however, using our new criteria, we were able to classify 100%. Seventy-eight percent had transformed migraine, 15.3% had chronic tension-type headache, and 6.7% had other headache disorders.

Classification of daily and near-daily headaches: Field trial of revised IHS criteria

1. The effect of central set on automatic postural responses was studied in humans exposed to horizontal support-surface perturbations causing forward sway. Central set was varied by providing subjects with prior experience of postural stimulus velocities or amplitudes under 1) serial and random conditions, 2) expected and unexpected conditions, and 3) practiced and unpracticed conditions. In particular, the influence of central-set conditions was examined on the pattern and magnitude of six leg and trunk electromyograph (EMG) activations and associated ankle torque responses to postural perturbations with identical stimulus parameters. 2. The scaling of initial agonist integrated EMG (IEMG) and torque responses to postural perturbation amplitude disappeared when perturbation amplitudes were randomized. This finding suggests that the initial magnitude of postural responses were centrally set to anticipated postural perturbation amplitudes based on sequential experience with the stimulus. 3. Expectation of postural stimulus amplitude had a significant effect on initial torque responses; subjects overresponded when a larger perturbation was expected and underresponded when a smaller perturbation was expected. Expectation of postural stimulus velocity had a smaller effect on initial torque responses, and subjects consistently overresponded when the velocity of the perturbation was unexpected. This difference in amplitude and velocity expectation may be because of the capacity to encode stimulus velocity, but not amplitude information, into the earliest postural responses of the current trial. The relative strength of amplitude and velocity central-set effects varied widely with individual subjects. 4. Central-set conditions did not affect initial EMG response latencies (100 +/- 20 ms, mean +/- SD) or the relative onset of proximal and distal agonists and antagonists. Unexpected or unpracticed stimulus amplitudes, however, were associated with significant late activation of ankle antagonist, tibialis. Thus errors in initial response magnitude because of central-set effects appear to be partially corrected by reciprocal antagonist activity. Agonist IEMG, however, did not always reflect significant changes in torque responses with central-set conditions. 5. Expectation of postural stimulus amplitude and velocity had two different types of effects on the magnitudes of postural responses: 1) a directionally specific, central-set effect consisting of either increased or decreased responses, depending on expectation of stimulus amplitude; and 2) a nonspecific enhanced response to novel stimulus velocities with a gradual reduction when a velocity was presented repeatedly. Two different neural mechanisms are proposed for these two adaptive effects. 6. Reduction of postural response magnitude and antagonist activity during practice may be partially explained by adaptive mechanisms based on expectation because of prior experience with stimulus velocity and amp

Influence of central set on human postural responses

Silberstein SD, Olesen J, Bousser M-G, Diener H-C, Dodick D, First M, Goadsby PJ, Gobel H, Lainez MJA, Lance JW, Lipton RB, Nappi G, Sakai F, Schoenen J & Steiner TJ on behalf of the International Headache Society. The International Classification of Headache Disorders, 2nd Edition (ICHD-II)—revision of criteria for 8.2 Medication-overuse headache . Cephalalgia 2005; 25:460–465. London. ISSN 0333-1024

The International Classification of Headache Disorders, 2nd Edition (ICHD-II)--revision of criteria for 8.2 Medication-overuse headache.

Headache characteristics are described in 139 patients with chronic daily or almost daily headaches due to regular intake of analgesics and the short- and long-term results of drug withdrawal. Drug-induced headache was described as dull, diffuse, and band-like, and usually started in the early morning. The mean duration of the original headache (migraine or tension headache) was 25 years; regular intake of drugs and chronic daily headache had started 10 and 6 years prior to withdrawal therapy, respectively. Patients took an average of 34.6 tablets or analgesic suppositories or antimigraine drugs per week containing 5.8 different substances. The drugs most often used were caffeine (95%), ergotalkaloids (89%), barbiturates (64%), and spasmolytics, paracetamol, and pyrazolone derivates (45%–46%). A total of 103 patients (68 migraine, 35 tension or combination headache) were available for interviews at a mean time interval of 2.9 years after an inpatient drug withdrawal programme. Chronic headache had disappeared or was reduced by more than 50% in two-thirds of the patients. Positive predictors for successful treatment were migraine as primary headache, chronic headache lasting less than 10 years, and regular intake of ergotamine. Drug intake was significantly reduced and patients used single substances more often. Patients who originally suffered from migraine, superimposed on the daily headache, also experienced a significant improvement in the frequency of the migraines and their intensity. Migraine prophylaxis through beta-blocking agents and calcium channel antagonists was more efficient after drug-withdrawal therapy.

Analgesic-induced chronic headache: long-term results of withdrawal therapy.

The present study used recordings of visual potentials evoked by pattern reversal (VEPs) to investigate the central effects of three drugs used in migraine prophylaxis: the calcium channel blocker nifedipine, the beta-1-selective blocker metoprolol, and the nonselective beta adrenoreceptor blocker propranolol. The study involved 58 patients with common or classical migraine who were treated in a double-blind randomized study over a period of 7 months, while the effectiveness of prophylactic treatment was recorded in headache diaries that were subjected to time series analysis. VEPs were recorded at the beginning of a 2-month baseline period without treatment, after 4 months of treatment, and at the end of a 3-month washout period. At baseline, migraine patients had significantly higher VEP amplitudes and longer latencies than did a group of 87 healthy control subjects. Patients were separated by statistical analysis into responders and nonresponders to each prophylactic treatment. Nifedipine had no effects on the frequency, intensity, and duration of migraine attacks, nor on amplitude and latency of the VEPs. In contrast, the use of beta blockers resulted in a significant decrease in VEP amplitude, both in responders and nonresponders, whereas VEP latency remained unchanged. VEP amplitudes returned to the initial values at follow-up in the nonresponders, but stayed at lower levels in responders. Beta blockers thus appear to have a significant effect on the increased excitability of the visual system in patients with migraine, although their action is not directly related to their reduction of migraine frequency.

Central effects of drugs used in migraine prophylaxis evaluated by visual evoked potentials.

Short, medium, and long latency EMG responses to muscle stretch from triceps surae and anterior tibialis muscles were recorded in normals and in 33 patients with Parkinson's disease. The latencies of all EMG responses except short latency were normal in patients with Parkinson's disease. The integrals of the medium latency responses in the stretched triceps surae muscle were significantly increased in patients. This result indicates a modulatory influence of the basal ganglia on medium latency EMG responses.

https://jnnp.bmj.com/content/jnnp/50/1/66.full.pdf

Medium and long latency EMG responses in leg muscles: Parkinson's disease.

A total of 78 chronic alcoholics were examined neurologically as well as by electroneurography, myography and posturography. Clinical signs of peripheral neuropathy were detected in 45% of these patients, with electromyographic and neurographic abnormality in 67% and 55% respectively. Clinical signs of cerebellar ataxia were found in 33% of our patients, whereas posturographic measurements of increased sway were recorded in 69%. The posturographic characteristics of cerebellar anterior lobe atrophy were observed in two-thirds of the latter patients. The severity of cerebellar-ataxia did not correlate with the degree of neuropathy. This lack of correlation is interpreted as an indication of different pathogenetic mechanisms acting on peripheral nerves and cerebellum.

Incidence of peripheral neuropathy and cerebellar ataxia in chronic alcoholics

Short and medium latency electromyographic (EMG) responses to stretch of the triceps surae muscle and long latency EMG responses (LL) in the anterior tibial muscle (TA) were evoked by toe-up tilt of a movable platform while standing or sitting, in normal subjects and patients with Parkinson's disease. With the stimulus parameters used (amplitude 4 degrees, velocity 50 degrees/s), LL in TA were absent in normals while sitting, but were present in 11 of the 12 patients with Parkinson's disease. In patients, LL latencies were identical in both positions. The results indicate that patients with Parkinson's disease have difficulty modulating long latency responses according to functional demands. Long latency responses in TA in the sitting position may correspond to the shortening reaction observed by others when much stronger stimuli were used.

E. Scholz

Papers

Analgesic-induced chronic headache: long-term results of withdrawal therapy.

Central effects of drugs used in migraine prophylaxis evaluated by visual evoked potentials.

Medium and long latency EMG responses in leg muscles: Parkinson's disease.

Incidence of peripheral neuropathy and cerebellar ataxia in chronic alcoholics

Increased shortening reaction in Parkinson's disease reflects a difficulty in modulating long loop reflexes