- Report a case of a healthy patient who endured a PICA infarction at high altitude

- Review known cerebrovascular changes that occur at high altitude to include hypoxemia, autoregulation and arrhythmias

High altitude exposure results in multiple compensatory responses, though cerebrovascular changes remains incompletely understood. Physiologic responses to hypoxemia and global changes in cerebral blood flow (CBF) that evolve during the course of high altitude exposure may result in alterations of cerebral peri-lesional blood flow. Additionally, several small case series have suggested an increased risk of arrhythmias such as atrial fibrillation at high altitude. For these reasons, determining the etiology of stroke in the setting of high altitude can be a challenge for the clinical neurologist.

Compensatory responses to extreme environments may impact stroke risk and should be considered when determining stroke etiology. We report a case of PICA infarction in an otherwise healthy patient with exposure to high altitude. The hypothesized etiologies include (1) impaired peri-lesion CBF in the setting of compensatory hypoxemic tachypnea and cerebral autoregulation and/or (2) paroxysmal atrial fibrillation precipitated by hypoxemia. We also provide a clinically relevant review of compensatory cerebrovascular changes at high altitude for the practicing neurologist.