Paroxysmal kinesigenic dyskinesia (PKD) is a paroxysmal movement disorder characterized by recurrent brief involuntary hyperkinesias such as choreoathetosis, ballism, athetosis or dystonia, triggered by sudden movements.
The prevalence is estimated to be 1/150,000 worldwide. PKD is the most common form of paroxysmal movement disorders. Males are more commonly affected than females (sex ratio of 3 or 4 to 1) in the sporadic form.
The age of disease onset is typically in childhood or adolescence with a peak in puberty. PKD is triggered by sudden movement from rest (such as rising from a chair or starting to walk, or by exercise) and is characterized by brief attacks of dystonia, chorea or athetosis movements preceded by aura (usually last less than 1 min) without alteration of consciousness. Attacks are often unilateral, but can alternate or be bilateral and their frequency is variable Some patients have additional neurologic disorders such as benign familial infantile convulsions (BFICs) or infantile convulsions (see these terms). Paroxysmal choreoathetosis is a description of the movement disorder described above (It is characterized as brief attacks of dystonia, chorea or athetosis movements) Two forms of PKD can, be distinguished, the primary PKD that can be further separated into the familial and the sporadic, and the secondary PKD that can be caused by many other medical conditions. Infantile convulsion and choreoathetosis (ICCA) is considered to be a variable form of PKD.
The exact etiology of the primary form of PKD is still unknown but PRRT2 (proline-rich transmembrane protein 2) gene (16p11.2) is believed to be the major causative gene. ThePRRT2gene encodes a protein that is hypothesized to interact with the SNAP25 protein which plays a role in presynaptic neurotransmitter release. It has been postulated that mutation in PRRT2 gene leads to a reduction of SNAP25 and this results in dysregulation of neurotransmitter release causing the symptoms seen in PKD. The most common underlying etiology for secondary cases comprises multiple sclerosis (see this term), cerebralvascular insufficiency, metabolic derangements (hypo- or hyperglycemia, hypocalcemia), orprevious trauma.
The clinical diagnosis of PKD relies on the following proposed criteria (1) identification of kinesigenic trigger of the attacks; (2) short duration of attacks (<1min); (3) no loss of consciousness or pain during attacks; (4) exclusion of other organic diseases and normal neurologic examination in the case of primary PKD; (5) control of attacks with phenytoin or carbamazepine, if tried; (6) age at onset between 1 year and 20 years, if no family history of PKD. Moreover, molecular genetic screening of the PRRT2 gene may help to confirm the diagnosis.
The differential diagnosis of PKD includes paroxysmal non-kinesigenic dyskinesia, juvenile myoclonic epilepsy, hyperekplexia, episodic ataxias, autosomal dominant nocturnal frontal lobe epilepsy, Glut-1 deficiency syndrome (see these terms) and shuddering attacks.
More than 60% of the patients with primary PKD have a family history of a similar disorder.PKD is mainly a familial disorderwith autosomal dominant inheritance and incomplete penetrance, but sporadic cases occur. Individuals with onset before 20 years, having a positive family history, should bescreened forPRRT2mutations.
Attacks are suppressed or dramatically reduced by low-dose anticonvulsant medication such as carbamazepine or phenytoin. Moreover, treatment based on caffeine citrate that may help to reduce the severity and frequency of attacks has been described in a single case report.
The prognosis of PKD is usually favorable with improvement of the attacks and even remission in adulthood. A gender difference in prognosis is also observed, that is woman have a better prognosis and higher chance of complete remission. An improvement of attacks can also be observed during pregnancy.
Last update: November 2013