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Clinical Summary

Acute mountain sickness (AMS) is a symptom complex that usually begins 12 to 24 hours after ascent to high altitude and consists of headache and one or more other symptoms, including gastrointestinal symptoms, fatigue and/or weakness, dizziness and/or lightheadedness, and difficulty sleeping. High-altitude cerebral edema (HACE) is a severe form of AMS, clinically defined by the presence of acute truncal ataxia, altered mental status, or both. Usually this occurs as a progression from AMS to HACE, but HACE may occur without antecedent AMS. If not effectively treated, HACE may progress to coma or death. Focal neurologic findings other than truncal ataxia are rare and should suggest another diagnosis, such as acute stroke or venous sinus thrombosis.

Management and Disposition

Treatment of HACE consists of immediate descent or evacuation, oxygen, and high-dose dexamethasone. Simulated descent using a portable hyperbaric bag (Gamow bag) may be more effective than oxygen alone and may be used in place of oxygen in field settings. Actual descent may be complicated by the inability of the patient to walk unassisted or at all. Patients with HACE may not ascend during the same trip and probably should not reascend to altitude for several months.


HACE-Related Ataxia. The patient (middle) developed HAPE and severe truncal ataxia at 5600 m (18,400 ft) in the Himalayas. He required full ambulatory assistance. Descent was started immediately. With descent, the patient’s breathing improved, but he remained too ataxic to walk. (Photo contributor: Ken Zafren, MD.)


  1. The first sign of HACE is usually truncal ataxia. This may be tested by assessing tandem gait (heel-to-toe walking).

  2. HACE may occur without symptoms of AMS.

  3. HACE is often associated with some degree of HAPE.


MRI Brain—HACE. MRI of a patient with HACE. Note the increased white matter signal, especially in the splenium of the corpus callosum, in this T2-weighted image. (Photo contributor: Ken Zafren, MD.)

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