The term "movement disorder" is used in two contexts: as a physical sign of involuntary movement or abnormal movement and to describe the syndrome that causes the involuntary movement .
In order to be able to discuss the different movement disorder syndromes, it is first imperative to define the types of movements that exist. This enables a common language among practitioners.
Tremor is defined as a rhythmic oscillation of a body part by alternating or synchronous contraction of agonist and antagonist muscles. It may be seen at rest or with action. It commonly affects the hands, but it may also involve the head, jaw, voice, tongue or lower limbs. Resting tremor occurs while the limb is not active. The typical resting tremor is the finger and wrist tremor in Parkinson's disease (PD). This is seen while the hand is resting on the patient's lap. Action tremor can be postural (seen during sustained posture, e.g. hands in the outstretched position), intention (during trajectory movement, e.g. finger-nose-finger), or task-specific (seen while performing a specific activity, e.g. only while writing).
Dystonia is an abnormal sustained muscle contraction, causing twisting or turning around one or multiple joints. It may be present in a variety of locations, including the neck (cervical dystonia/torticollis), eyelids (blepharospasm) or vocal cords (spasmodic dysphonia). Dystonia can be focal, segmental or generalized. An example of focal limb dystonia is writer's cramp. In segmental dystonia, an entire limb or trunk is involved. Generalized dystonia is multi-focal, involving several body parts.
Myoclonus is defined as a sudden, brief, shock-like involuntary muscle contraction or inhibition. Positive myoclonus occurs with active muscle contraction, while negative myoclonus causes inhibition of the activated muscle. An example of negative myoclonus is asterixis (brief interruption of muscle contraction in the extended arm and wrist). Myoclonus is classified by the body part involved (focal or multi-focal) and in relation to its etiology
(e.g. post-anoxic) or site of origin (cortical or subcortical). Some types of myoclonus are stimulus sensitive or action induced.
Chorea is derived from the Greek word meaning "dance". Chorea consists of complex involuntary movements resembling exaggerated fidgetiness. The movements are usually generalized, purposeless and absent during sleep. Choreoathetosis is the term used when the movements are slow and writhing. In mild cases, the choreatic movements can be blended into natural movements and appear more purposeful.
Ballismus is characterized by large-amplitude, proximal chorea. At times, it can be quite violent. Onset is often sudden and typically related to an infarct in the contralateral sub-thalamic nucleus. It usually occurs on one side of body, hence the term hemiballismus. Hemiballismus usually evolves into the less violent hemichorea over time.
Tics are temporarily suppressible movements seen in Tourette's syndrome. The frequency and severity of tics are exacerbated after voluntary suppression. This is a rebound effect. Tics can be motor or vocal in nature. Simple motor tics are isolated, brief and sudden movements involving one body part. Complex motor tics may involve more than one body part and may have a component of dystonia or tremor. Complex motor tics may take the form of purposeful movements. A complex motor tic that is an obscene gesture is termed copropraxia. A simple vocal tic may be a grunt or a throat clearing. Complex vocal tics may be more elaborate vocalizations, words or phrases. When the words include profanities, the term coprolalia is used.
Bradykinesia literally means slowness of movement. It is a term used to describe slowness of voluntary movements, such as that seen in PD. The amplitude of fine movements is typically decreased. When there is a lack of movement, the term akinesia is used. Akinesia is frequently used interchangeably with bradyki-nesia.
Freezing is an arrest of gait and is usually associated with bradykinesia. It may occur during gait initiation, when approaching an obstacle or when attempting to turn. Freezing is a specific gait phenomenon that is often seen with PD.
Dyskinesia means abnormal involuntary movement. It is frequently seen in patients with
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