Paroxysmal kinesigenic dyskinesia (PKD) is characterized by sudden, brief dystonic or choreiform movements triggered by abrupt movement. Pathogenic heterozygous mutations in the PRRT2 gene are responsible for approximately 50% of cases. PRRT2 mutations have variable phenotypes: benign familial infantile epilepsy, infantile convulsions with paroxysmal choreoathetosis, episodic ataxia, and hemiplegic migraine. PRRT2 mutations can have overlapping features with PNKD (non kinesigenic).

A 19-year-old Asian/Caucasian male cello player with history of motor tic disorder and ADHD presented to our clinic after he experienced sudden-onset, complex choreiform, ballistic movements during an orchestra performance in front of a live audience (see video). His "tics" began at age 7 with brief facial movements, which were partially suppressible and preceded by an urge. A few years later, he developed complex, generalized choreiform movements, lasting up to 30 seconds and occurring up to five times per day, which were non-suppressible, preceded by a sense of tension in his legs, and increased in frequency during stressful times. Genetic testing detected a pathogenic heterozygous mutation in the PRRT2 gene at Exon 2, c.649dup (p.Arg217Profs*8). Initiation of carbamazepine resulted in resolution of symptoms but also alteration of pitch perception (decreased by a semitone), a previously reported idiosyncratic side effect of carbamazepine, normalizing within days of medication discontinuation. He was then treated with lacosamide 100mg daily, completely ameliorating symptoms without adverse effects.

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, which is likely only appreciated by patients with absolute pitch. Finally, it raises the possibility of an association between PKD and stuttering since there is a strong family history of stuttering in this patient.