Tremor is defined as a rhythmic and oscillatory movement of a body part with a relatively constant frequency and variable amplitude. It is caused by either alternating or synchronous contractions of antagonistic muscles. Tremor is the most common of all movement disorders, occurring from time to time in most normal individuals in the form of exaggerated physiologic tremor .
This topic will cover the classification, clinical features, diagnostic evaluation, and treatment of tremor. The treatment of essential tremor (ET) is discussed separately. (See "Pharmacologic treatment of essential tremor" and "Surgical treatment of essential tremor".)
Tremors may be broadly classified into static and action tremors (table 1). Static tremors may be further divided into those occurring at rest (resting tremor) and those occurring with the head and limbs held in a fixed posture (postural tremor) (table 2 and table 3). Action tremors remain unchanged during the course of a voluntary movement, while intention tremors increase during the course of goal-directed movement. The term kinetic tremor has been used to designate action and intention tremor.
Parkinson disease (PD) and other parkinsonian syndromes are the most common causes of resting tremor. This tremor is evident with the affected body part supported and completely at rest and temporarily dampens or disappears during voluntary activity. Resting tremors usually fluctuate in amplitude and may appear and disappear depending upon the degree of patient repose, whether the patient feels he or she is under observation, and other unknown factors.
Resting tremor is typically less disabling than postural, action, or intention tremors because of its absence during voluntary activity. However, the tremor may quickly reappear as soon as the body part assumes a new resting posture and may therefore interfere with the use of eating utensils, handwriting, typing, and other purposeful postures or movements. In such cases, resting tremor is more of a handicap or disability than pure resting tremor, which is of greater cosmetic concern.