Paroxysmal Kinesigenic Dyskinesia

Paroxysmal kinesigenic dyskinesia (PKD) is a form of paroxysmal dyskinesia (see this term), characterized by recurrent brief involuntary hyperkinesias, such as choreoathetosis, ballism, athetosis or dystonia, triggered by sudden movements.

Epidemiology

The prevalence is estimated to be 1/150,000 worldwide. PKD is the most common form of paroxysmal dyskinesia. Males are more commonly affected than females (sex ratio of 3 or 4 to 1) in the sporadic form.

Clinical description

The age of disease onset is typically in childhood or adolescence with a peak in puberty. PKD is triggered by a 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 (that 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 epilepsy (BFIE) (see this term). Infantile convulsion and choreoathetosis (ICCA; see this term) is considered to be a variable form of PKD.

Etiology

The exact etiology of PKD is still unknown but the PRRT2 (proline-rich transmembrane protein 2) gene (16p11.2) is believed to be the major causative gene. The PRRT2 gene 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 mutations in PRRT2 lead to a reduction of SNAP25 resulting in the dysregulation of neurotransmitter release, thus causing the symptoms seen in PKD.

Diagnostic methods

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 attempted; and (6) age of 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.

Differential diagnosis

The differential diagnosis of PKD includes paroxysmal non-kinesigenic dyskinesia, juvenile myoclonic epilepsy, hyperekplexia, episodic ataxia, autosomal dominant nocturnal frontal lobe epilepsy, encephalopathy due to GLUT1 deficiency (see these terms) and shuddering attacks.

Genetic counseling

More than 60% of the patients with PKD have a family history of a similar disorder. PKD is mainly a familial disorder with autosomal dominant inheritance and incomplete penetrance, but sporadic cases occur. Individuals with onset before 20 years of age, and having a positive family history, should be screened for PRRT2 mutations.

Management and treatment

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.

Prognosis

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, with woman having a better prognosis and a higher chance of complete remission. An improvement of attacks can also be observed during pregnancy.