Objective: To present a novel case of transient hemiballismus in a fast jet pilot occurring shortly after exposure to extreme G forces.

Background: Hemiballismus is classically associated with lesions of the subthalamic nucleus (STN). Stroke is the most common cause and slow recovery is expected. Transient hemiballismus has also been reported in the context of ischaemia-reperfusion injury, subclavian steal syndrome and hyperglycaemia. The arterial blood supply to the STN relies on the perforating branches of the anterior choroidal artery, posterior communicating artery and posteromedial choroidal arteries. These arteries lie at the base of the brain, which may render them susceptible to compression under conditions of high positive G.

Methods: We present a case of a previously healthy test pilot who experienced an episode of transient hemiballismus approximately one minute after exposure to greater than positive 9 G.

Results: The pilot was on a test flight during which he had sustained at least 10 greater than positive 9 G events. After one of these manoeuvres, he had been flying level for one minute when he lost control of his right arm. It started “spasming” powerfully, causing him to lose grip of the control column. He described his arm shooting up to the level of the shoulder and flailing up and down in an arc between his waist and his head. The episode lasted around 10 seconds in total and he subsequently returned to the airstrip and landed safely. He never experienced a similar phenomenon again.

Conclusions: This case of transient hemiballismus in the context of extreme G flying is unique in the literature. The precise aetiology is unknown but may relate to reperfusion injury to the STN.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/transient-hemiballismus-in-a-fast-jet-pilot/