Altitude Illness - Cerebral Syndromes Clinical Presentation

Updated: Feb 22, 2019
  • Author: N Stuart Harris, MD, MFA, FACEP; Chief Editor: Joe Alcock, MD, MS  more...
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AMS is a syndrome of nonspecific symptoms with a broad spectrum of severity. AMS occurs in nonacclimatized individuals within the first 48 h after ascent to altitudes above 2,500 m, especially after rapid ascent (1 d or less). Symptoms usually begin a few hours after arrival at the new altitude but may arise as much as a day later, often after the first night's sleep. Headache is the principal symptom, typically frontal and throbbing. Gastrointestinal symptoms (anorexia, nausea, or vomiting), and constitutional symptoms (weakness, lightheadedness, dizziness, or lassitude) are common. AMS is similar to an alcohol hangover, or to a nonspecific viral infection, but without fever or myalgias.

Fluid retention is characteristic of AMS, and individuals with AMS often report reduced urination, in contrast to the spontaneous diuresis observed with successful acclimatization. As AMS progresses, the headache worsens, and vomiting, oliguria, and increased lassitude develop. Ataxia and altered level of consciousness herald the onset of clinical HACE.

Using the Lake Louise consensus criteria, the diagnosis of AMS requires headache plus at least one of the following symptoms: gastrointestinal (anorexia, nausea, vomiting) or constitutional (lightheadedness, dizziness, weakness, fatigue). [3]  Most conditions similar to AMS can be excluded by history and physical examination. Onset of symptoms more than 3 days after ascent, lack of headache, or failure to improve with descent, oxygen, or dexamethasone suggests another diagnosis. Dehydration is commonly confused with AMS, as it can cause headache, weakness, nausea, and decreased urine output.

The most common history in HACE is a person continuing ascent despite symptoms of AMS; however, rarely, it may develop in the absence of AMS after a very rapid ascent or at extreme altitude in an apparently acclimatized person. Also, HACE commonly occurs in conjunction with HAPE.


Physical Examination

Acute mountain sickness

Patients may appear ill but otherwise have no characteristic physical findings. Neurologic examination (especially mental status and gait) is normal. Heart rate and blood pressure are variable and nondiagnostic. Pulmonary crackles may be present in some patients, but oxygen saturation will be normal or, at most, slightly lower than acclimatized persons at the same elevation. Fever is absent. Funduscopic examination may reveal retinal hemorrhages, but these are not specific to AMS. [4]  Peripheral and facial edema may be present, particularly in women.

High-altitude cerebral edema

In a patient with symptoms of AMS who develops gait ataxia (ie, unable to walk heel-to-toe in a straight line) or mental status changes, HACE is the diagnosis until proven otherwise. Immediate treatment and descent is indicated. Regardless of AMS symptoms, a combination of ataxia and mental status changes suggests HACE. Aside from the aforementioned gait ataxia and mental status change, the neurologic examination findings are otherwise normal. In rare cases, focal neurologic signs (eg, cranial nerve III palsy, cranial nerve VI palsy) appear in end-stage HACE, although they are more suggestive of other causes of focal deficits at altitude (eg, stroke, transient ischemic attack [TIA], migraine, brain neoplasm).



Symptoms of HACE, particularly ataxia, commonly persist for days to weeks after descent. In rare cases, patients may have long-term neurologic deficits after severe or prolonged HACE.