NEUROLOGY

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Tremor

Tremor is a rhythmic oscillatory, non-purposeful movement of a body part produced by regular or sequential contractions of opposing muscles.

Pathogenesis

Like others movement disorders tremor is believed to result from dysfunction of basal ganglia(caudate nucleus, putamen, globus pallidus, subthalamic nucleus and substantia nigra).

Clinical Features

Tremors are characterized by involuntary contractions of muscle groups producing oscillatory movements at one or more joint that can be quantified by the number of movements per second(expressed in Hertz). Some importants questions have to be answered in the characterization of tremors:

• Is there relation to voluntary motor activity?
  
• Does it occurs at rest?
  
• Does it occurs during maintenance of a particular posture?
  
• Is it enhanced by emotional stress?
  
• Does it disappears at sleep?

These questions are important because tremors characteristically are enhanced by emotional stress and disappears during sleep. Furthermore, tremors are best characterized by its relationship to voluntary motor activity in:

Postural Tremor

Is that present with the limb outstretched and typically vanish with the limbs in a resting position. There are two main causes of postural tremor; physiologic and essential.

Physiologic tremorhas a frequency of 8 to 12 Hz and is a normal finding although its physiologic basis is uncertain. It may be enhanced by fear, anxiety, following physical activity. Is a common find in thyrotoxicosis and can also result from poisoning with substances such as lead, arsenic and carbon monoxide. There is no specific treatment.

Essential tremoris the most common type of symptomatic tremor and is inherited in an autossomal dominant pattern. Although frequently referred as benign essential tremor, it may be disabling often causing spilling of liquids and interfering with handwriting. It also frequently involves the head and voice.

Beta-adrenergic blocking drugs(propranolol at 80 to 240 mg per day) are the most effective agents in the its treatment.

Resting Tremor

is a slow tremor(4 to 6 Hz) which is present at rest and disappears with action. This type is characteristic of parkinsonism whether the disorder is idiopathic or secondary(toxic or drug induced). The association with rigidity or hypokinesia on physical examination help in differentiate the tremor of parkinsonism from others forms. It commonly begins in the hand or foot, where it takes the form of rhythmic flexion-extension of the fingers. Tremor in the hands may appear as a "pill rolling" maneuver(opposing circular movements of the thumb and index finger). Other less common causes include Wilson's disease and poisoning with heavy metals(mercury).

The treatment of tremor should be based on its cause. In Parkinson's disease levodopa or anticholinergics drugs achieve good results

Intention Tremor

Is a tremor that occurs during activity and is often more marked as the limb nears the target. This form of tremor is sometimes mistaken for limb ataxia, but the latter has no rhythmic oscillatory component.

Intention tremor results from a lesion affecting the superior cerebellar peduncle, as a manifestation of toxicity of certain sedatives or anticonvulsant drugs or alcohol. It is also seen in patients with Wilson's disease. There is no medical treatment and stereotatic surgery of the ventrolateral nucleus of the thalamus is sometimes helpful.

References