Various complex classifications have been proposed for this group of disorders [see Fahn (108) for a summary and a history of terminology]. The most clinically relevant and simplest is used here. Most of the literature describes familial cases, which are easier to diagnose (especially once one or more affected family members are known) and are possibly more interesting to report than sporadic cases. However, it is our clinical impression that most people with paroxysmal dyskinesias are sporadic, and many cases do not fit exactly into the classical descriptions outlined.
Paroxysmal kinesigenic dyskinesia (PKD).
Typically, onset is in early childhood or adolescence with episodes of choreoathetosis, dystonia, or a mixed pattern. Attacks tend to become less frequent or remit totally in adult life. Attacks last seconds to 5 minutes and are precipitated by sudden movements, change in position, or change in movement velocity (109). Getting up from a chair or getting out of a car are frequent triggers. Consciousness is retained, and some individuals may have a brief nonspecific warning or aura prior to an attack. Interictal examination is normal. Diagnosis is based on history, and a videorecording of events is invaluable. Carbamazepine is often highly effective in small doses. A family history of similar events exists in about a quarter of patients, with autosomal dominant inheritance in many families. Linkage to several overlapping but distinct loci around the pericen-tromeric region of chromosome 16 has been reported but the genes involved have not been identified to date (110,111). In some families, the paroxysmal dyskine-sia is associated with benign familial infantile convulsions (102,104). This has been reported as the infantile convulsions and choreoathetosis syndrome (ICCA). However, the movement disorder may include paroxysmal dystonia and is, therefore, better classified as a paroxysmal dyskinesia.
(PNKD). Attacks are often longer in PNKD and may last 2 minutes to several hours or even 2 days. This type is sometimes referred to as paroxysmal dystonic choreoa-thetosis (PDC). The attacks are often markedly dystonic and occur spontaneously, although in adults alcohol, caffeine, and stress are frequent precipitants. Differentiation from epileptic seizures is easier and treatment with antiepileptic medications is less effective than in true epilepsies. Inheritance is usually autosomal dominant, and linkage has been reported to chromosome 2 (112,113).
Paroxysmal exercise induced dyskinesia (PED). Events occur after several minutes of exercise, usually 10 to 15 minutes or more, not at the initiation of movement, as in PKD (114). Typically, the part of the body that has been doing most exercise becomes dys-tonic. The abnormal movement resolves gradually with cessation of the exercise, over 5 to 30 minutes (intermediate between PKC and classical PDC). Antiepileptic medications are not generally helpful although acetazo-lamide has been effective in some families (114).
Benign paroxysmal torticollis in infancy (BPT). In BPT, infants have attacks of retro-, latero-, or torticollis that may last minutes to hours (115). In rare instances, they may last days. Typically, attacks begin in early infancy and remit by age 5. They may be triggered by movement, often in the early morning, and are heralded by irritability, pallor, vomiting, and in older children, clear ataxia. BPT is both a movement disorder and a migraine equivalent (116). Two patients with BPT in a recent series came from a family with familial hemiplegic migraine linked to a mutation in the voltage-gated calcium channel gene CACNA1A on chromosome 19 (117).
Benign paroxysmal tonic upgaze of childhood. Benign paroxysmal tonic upgaze of childhood (118) typically presents in infants of less than 3 months with prolonged periods (hours to days) of sustained or intermittent upgaze deviation. Later, ataxia is associated. The episodes remit with in a few years but are associated with psychomotor retardation or language delay in up to 80% of cases (119).
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