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| Basal Ganglia and Movement Disorders |
Tremor
Tremor is a rhythmic, oscillatory, involuntary movement caused by the alternating activation of agonist and antagonist muscles. The etiology of tremor is diverse and includes hereditary (familial tremor), degenerative (Parkinson disease), metabolic (thyroid, parathyroid, or hepatic disorders and hypoglycemia), toxins (nicotine, mercury, lead, carbon monoxide, manganese, arsenic, toluene), illicit drug use or medication-induced (neuroleptics, tricyclics, lithium, cocaine, alcohol, adrenaline, bronchodilators, theophylline, caffeine, steroids, valproate, amiodarone, thyroid hormones, vincristine), peripheral neuropathies (Charcot Marie Tooth disease, RoussyLevy syndrome, complex regional pain syndrome), and psychogenic disorders.
Tremor
may be classified as rest, postural, and intentional, according to its
relation to activity. Rest tremor is best seen when the limbs are relaxed,
resting in the patient’s lap; when necessary, mental exercises may help to
“bring out” the dyskinesia. A 3
to 5Hz rest tremor is a
characteristic feature of Parkinson disease (“pillrolling” tremor), in which it often starts
asymmetrically. One important feature of this type of tremor is its
disappearance or improvement with limb movement. Although the tremor may become
bilateral with disease progression, it commonly remains more severe on the
initially affected side.
Postural
tremor is seen when the limbs are actively maintained in a particular posture
against gravity and disappears when the limbs are at rest. Examples of postural
tremors are essential tremor, drug
or toxininduced tremor, metabolic conditions, and alcohol withdrawal states. Physiologic
tremors are also postural in nature and are seen in all individuals at a
frequency of 8 to 12 Hz. They are enhanced by caffeine, fear, or anxiety.
Essential
tremor is a sporadic condition, but in approximately
50% of those affected, a family history may be elicited (familial tremor). Typically,
a 5 to 8Hz tremor is present
bilaterally in the hands or arms. A tremor of the head or vocal cords is also
common. Patients often noticed an improvement in tremor after having a sip of
alcohol. Most cases are mild and do not require treatment, but when necessary, propranolol, primidone, or
certain antiepileptic drugs may be effective.
Intention
tremor is the tremor most commonly associated with disease of the cerebellum and its associated pathways, but it may be
seen in patients with advanced essential or familial tremor. The tremor, which
occurs during movement, can be unilateral or bilateral, depending upon the
cerebellar lesion, and may affect upper and lower limbs. It has a frequency of
2 to 4 Hz and characteristically worsens as the limb approaches its target (endpoint accentuation).
Another term used for cerebellar outflow tremor is rubral tremor. We discourage
the use of such a term because these are not specific for lesions found only at
the red nucleus. We prefer the term cerebellar outflow tremor to
describe intention, rubral, or cerebellar tremor.
A “wing beating” tremor has been described in patients with Wilson disease and in patients with multiple sclerosis or stroke involving the superior cerebellar peduncular region. In these patients, the tremor is most prominent when flexing the forearms at the elbows and elevating the shoulders laterally to reach a 90degree angle in the fully abducted position. This “phenomenology” is similar to that in cerebellar outflow tremor, particularly when severe, and probably reprsents involvement of cerebellothalamofugal pathways.
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