Tremor is an involuntary alternating movement, which is described in terms of rhythmicity (regular or irregular), amplitude (small or large), frequency (slow or fast), and which parts of the body are affected. There are many terms for types of tremor. A rest tremor is present at rest. An action tremor is present with movement or posture. There are several types of action tremor. A postural tremor is present with a position held against gravity, such as holding the arms outstretched. A kinetic tremor is present during movement. All of the previous tremors may occur with basal ganglia dysfunction, and some with lesions of other brain areas. An intention tremor is a type of kinetic tremor that appears when a movement approaches a target, such as near the finger or nose during finger-to-nose testing. Intention tremor usually occurs with dysfunction of the lateral cerebellum or its connections, usually with other findings of limb ataxia.
Basal ganglia dysfunction probably causes dystonia, which involves involuntary sustained contraction of one or more muscles causing abnormal movement or posture. Dystonia may be focal or generalized, and it may be episodic or continuous. Muscles chronically affected by dystonia may develop hypertrophy (increased bulk), and a dystonic tremor may occur, which is an irregular tremor produced with movements or positions that lengthen the affected muscles.
Several other dyskinesias may occur with basal ganglia dysfunction, and sometimes with lesions of other brain areas. Chorea refers to involuntary, fast, irregular, mostly distal limb movements that may resemble dancing. Athetosis refers to involuntary, slow, writhing, mostly distal limb movements that may resemble the movement of snakes. Myoclonus refers to involuntary, small, fast movements (a “jerk”), usually of the torso and proximal limbs simultaneously. Ballism refers to involuntary, fast, large, proximal limb movements. Tics are seminvoluntary movements or vocalizations that relieve a progressively uncomfortable sensation; tics may be briefly suppressed with concentration.