Objective:

We describe a patient who presented with unilateral dystonic episodes triggered by sudden movements. Genetic testing revealed a variant in NBEA. We describe their presentation, clinical course and management with accompanying video. 

Background:

Paroxysmal Kinesogenic Dyskinesia (PKD) is characterized by brief, recurrent involuntary hyperkinesias precipitated by sudden movements. Episodes are short, without pain or loss of consciousness with an identifiable trigger typically occurring multiple times a day. Episodes respond to treatment with carbamazepine or phenytoin. Several causative genes have been identified. NBEA has been identified as a cause of familial PKD.  

Design/Methods:

A 15-year-old boy developed recurrent episodes of extensor posturing of his right arm which later spread to his legs and trunk triggered by sudden movements or change in velocity of movement. These episodes initially occurred about eight times a day and later increased in frequency. Prior to these episodes, there is a sensation of muscle tension, and some attacks may be prevented by slowing down his movements. There was no personal or family history of other abnormal movements, seizures, ataxia, developmental delays. Neurological exam was normal in between episodes.    

Results:

He was treated with Carbamazepine 600 mg BID with good symptom control, however, was discontinued due to drug related fever and rash. Treatment with Levetiracetam up to 2000mg BID led to mild improvement of symptoms. He was then treated with Oxcarbazepine 1200 mg BID with complete symptom control without significant adverse effects. Research trio exome sequencing revealed a de novo missense variant in NBEA. The variant is absent from gnomAD and ClinVar, has a CADD score of 25.7, and involves a well-conserved amino acid. No variants in other known PKD genes were identified.  

Conclusions:

NBEA variants can cause PKD and should be considered in patients who test negative for PRRT2.  PKD caused by NBEA variants can be completely treated with Oxcarbazepine.