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ESSENTIAL TREMOR 30 June 2000 Page 1 of 2 Neurology 2000; Volume 54, Supplement 4, Pages 1-45: Feeling that scientific knowledge about essential tremor is unduly sparse and its study neglected, a group of prominent experts decided to write down all they know about it at present, which is summarized in articles comprising Supplement 4 of the journal Neurology for this year, as follows (titles edited): Deuschl G, Koller W Introduction 1 Elble R Diagnostic Criteria 2 Bain P et al Diagnostic Criteria 7 Findley L Epidemiology 8 Deuschl G, Elble R Pathophysiology 14 Jankovic J Clinical Characteristics 21 Bain P Tremor Measurement and Quality of Life 26 Koller W et al Pharmacological Treatment 30 Pahwa R et al Surgical Treatment 39 (not listed) Support Organizations 45 Since Supplement 4 is printed as a stand-alone booklet, I shall try to offer highlights of the document as a whole, rather than review each contribution separately. Much of the information has been published by these authors before, but many interesting bits and pieces are new to me. Owing to the current state of knowledge about ET, the various authors here don't necessarily agree. Essential Tremor (ET) is known as an involuntary oscillation involving skeletal muscles, nearly always of arms or hands, and less often the head, legs, face, voice, or trunk. The frequency is taken to be in the range 4-12Hz, possibly related somewhat to the patient's age. For purposes of study and diagnosis, several kinds of tremor are defined, such as resting, postural, kinetic, isometric, and action tremors. For ET research, something called harmaline is found to induce similar tremor in animals, and in animals the part of the brain affected by harmaline is the inferior olive. From this, workers infer that ET in humans may be an oscillation of the olivo- cerebellar-thalamo-cortical loop. Another discovery from neurophysiological studies, that should be useful in diagnosis, is that the waveform (time history) of tremor motion in PD is distinctly different from that of ET and other tremors. But, ET may on occasion occur together with PD. Essential Tremor (ET) may afflict up to 5% of people over 40. Genetic origin has long been suspected, simply because no plausible environmental cause is known. There are instances of familial clusters, but most cases seem to be sporadic. Recently, though, the first genes related to ET have been found. Probably there are many, leading to many variations in the disorder. The articles here hardly address such questions as onset age or rate of progression. ESSENTIAL TREMOR Page 2 of 2 Diagnosis is difficult, partly because the medical community is just now reaching detailed agreement on a definition of ET. ET seems to be an uncontrolled oscillation in the signal network of the central nervous system, likely involving the cerebellum. The range of symptom severity is wide, disabling enough in some to cause retirement from work, but many of those who fit the current definition of ET don't seek medical attention. Proposed criteria for diagnosis of ET are based largely on exclusion of other disorders. For example if the tremor is accompanied by rigidity, bradykinesia, or gait disturbance, or if it is unilateral, the diagnosis would lean toward PD. The most popular drugs for ET are "beta-blockers" such as propranolol (Inderal) or the anticonvulsant agent primidone (Mysoline), although many others are being tried. Alcohol also is effective, but the mechanism of action is unknown. As with PD, stereotactic surgery, utilizing either lesioning or chronic stimulation (DBS), is effective against ET, but usually reserved for cases where drug therapy has failed. The current site of choice is the ventral intermediate nucleus (VIM) of the thalamus. Bilateral thalamotomy is usually avoided, due to high risk of adverse effects, but bilateral DBS of the same site seems to be safe. -- J. R. Bruman (818) 789-3694 3527 Cody Road Sherman Oaks, CA 91403-5013