High-altitude cerebral edema (HACE) is a rare condition in which brain swelling occurs as a result of failure to acclimate while ascending to high altitudes. HACE presents with progressive decline in mental status with impaired / ataxic gait and lethargy in patients with acute mountain sickness.

The clinical presentation of acute mountain sickness is nonspecific and develops in unacclimated patients who rapidly ascend to high altitudes, resembling a hangover with headache, fatigue, lightheadedness, anorexia, nausea, and vomiting. Symptoms are most severe after the first night, and they tend to resolve within the first 24 hours if there is no further ascent.

HACE is a complication of acute mountain sickness. Initial signs of HACE may be subtle. Onset can be rapid (hours) or may present a few days after development of acute mountain sickness. Without recognition and management, HACE can be lethal (patients typically die within 2 days if immediate descent and prompt treatment do not occur). Even with treatment, full recovery may take days to weeks.

HACE is encountered in 0.1%-2% of unacclimatized individuals exposed to altitudes, most commonly >3000-4000 meters (about 10 000 feet), although it can occur as low as 2100 meters (about 6900 feet). HACE is commonly associated with high-altitude pulmonary edema (HAPE) as well.

HACE can affect any patient of any age; young males are considered more at risk because of behavioral reasons (ie, pushing themselves despite symptoms).