Acute mountain sickness is a disease of delayed-onset hypoxemia that occurs in unacclimatized individuals typically 6-12 hours after arrival at a high altitude (2000 meters [about 6500 feet] or higher). Incidence increases with increasing altitudes of initial exposure. It is a precursor to the more severe disease high-altitude cerebral edema (HACE).

The clinical presentation of acute mountain sickness is nonspecific, 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.

While the condition can affect anyone (all ages, male and female), women are more commonly affected as are individuals who regularly experience headaches. Those who have experienced acute mountain sickness in the past are also more susceptible. Patients 50-60 years of age and older may be less affected by acute mountain sickness.

HACE presents with progressive decline in mental status with impaired / ataxic gait and lethargy in patients with acute mountain sickness. Initial signs 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.

Related topic: High-altitude pulmonary edema (HAPE)