High altitude illness describes a group of syndromes which can occur due to rapid ascent to high altitudes (>2500 m) without sufficient acclimatisation.
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Epidemiology
High altitude illness typically develops in hikers and mountain climbers with rapid high altitude ascension.
Clinical presentation
High altitude illness is typically grouped into three categories based on its clinical presentation 1,3:
acute mountain sickness: headache, fatigue, and nausea, which can progress to...
high altitude cerebral edema (HACE): altered mental status with truncal and gait ataxia
high altitude pulmonary edema (HAPE): dyspnea and hyperventilation
Pathology
The main factor involved is the relatively low partial pressure of oxygen in altitudes above 2500 m.
In high altitude cerebral edema, the low partial pressure of oxygen causes cerebral vasodilation and disruption of the blood-brain barrier with resultant increased vascular permeability causing vasogenic edema. The internal radical formations also deactivate the sodium-potassium ATP dependent pump leading to cytotoxic edema 1-3.
In high altitude pulmonary edema, there is uneven hypoxic vasoconstriction that leads to pulmonary edema 1-3.
Radiographic features
Radiographic features of high altitude pulmonary edema are discussed separately, see that article for more details.
MRI
Evidence of high altitude cerebral edema on MRI brain include 1:
T2/FLAIR: high signal in the subcortical white matter and corpus callosum
SWI: microbleeds in the subcortical white matter
DWI: may reveal multifocal small diffusion signal regions, which often demonstrate reversibility
Treatment and prognosis
Medications such as dexamethasone and acetazolamide should be administered to patients with high altitude cerebral edema, however, the definitive treatment is descent to a lower altitude 3. If left untreated, high altitude cerebral edema can be a fatal condition.
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