Paroxysmal Asymmetric Dystonic Arm Posturing—A Less Recognized but Characteristic Manifestation of ATP1A3‐related disease

Background: ATP1A3 mutations cause a wide clinical spectrum, and are one of the "commoner rare diseases". Methods: Case series of four patients with ATP1A3 mutations. Results: The patients displayed characteristic episodes of dystonic arm posturing, involving a dystonic, flexed arm held in front of the body or close to the body, but with the hand raised upwards. Other attacks manifested with arm extension, either beside the body or reaching upwards. Dystonic posturing occurred paroxysmally, with no neurological signs between attacks, or combined with other signs like chorea, ataxia, and hypotonia. Conclusions: While previous diagnostic criteria have not included paroxysmal or episodic dystonia, recent expert consensus has proposed to include alternating or paroxysmal dystonia as major feature calling for ATP1A3 genetic testing. Attacks of marked arm flexion posturing, either paroxysmal or as episodic exacerbation of mild pre-existent dystonia, are a characteristic clue to ATP1A3-related disease.