Objective: To report a case of tics associated with paroxysmal kinesigenic dyskinesia in a patient with PRRT2 mutation.

Background: Paroxysmal kinesigenic dyskinesia (PKD) is characterized by sudden, brief dystonic or choreiform movements triggered by abrupt movement. A pathogenic heterozygous mutation in the PRRT2 gene is responsible for approximately 50% of PKD cases. PRRT2-PKD is more common in males (1.5:1 male to female ratio) and in the Asian population. Onset is typically in childhood or adolescence.

Method: A 19-year-old Asian/Caucasian male cello player with history of ADHD presented to our clinic after he experienced sudden-onset, complex choreiform, ballistic movements during an orchestra performance. His symptoms first began at age 9 with abnormal facial expressions and mouth opening, diagnosed as tics, but without response to clonidine, guanfacine, or topiramate. He subsequently developed head and neck movements, followed by movements of all four limbs and the trunk. He endorses partial suppressibility and inconsistent pre-monitory urge (an aura he described as “tightness in muscles”). He has never had vocal tics. Triggered by sudden movements and exacerbated by stress, movements occur with a frequency of 10-15 times per day, with a maximal duration of 30 seconds. There is no family history of movement disorders, but there is a positive family history for stuttering in his father, paternal uncle, and paternal grandfather. His mother and brother both have ADHD and Bipolar disorder.

Results: A dystonia panel returned a positive pathogenic heterozygous mutation in the PRRT2 gene at Exon 2, c.649dup (p.Arg217Profs*8). This frameshift mutation causes a premature translational stop signal which results in an absent or disrupted protein. A trial of carbamazepine resulted in resolution of symptoms but also transient alteration of pitch (decreased by a semitone), which resolved after the medication was discontinued.

Conclusion: Tics have rarely been reported as co-occurring with PKD, but in one observational study, tics were present in 79% of patients with PKD, making this an under-recognized phenomenon. Additionally, this case highlights a rare side effect of carbamazepine, alteration of pitch perception, which is likely only appreciated by patients with absolute pitch, such as this patient. Finally, it raises the possibility of an association between PKD and stuttering since there is a strong family history of stuttering in this patient. Paternal genetic testing is pending.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/paroxysmal-musicians-dyskinesia/