Acute mountain sickness is a type of altitude sickness which develops within a few hours of an unacclimatized individual ascending rapidly to a high altitude. It is characterized by sudden onset of a bitemporal headache, nausea, fatigue, dizziness and can be life-threatening with the development of cerebral or pulmonary edema.
Acute mountain sickness (AMS) is a common form of altitude sickness which affects between 10 to 80% of individuals climbing to high altitudes     . Symptoms are variable and usually commence within 24 hours of an unacclimatized individual ascending rapidly to altitudes > 8000 feet. Common symptoms include headaches, dizziness, vomiting, anorexia, fatigue, and insomnia  and they are due to the hypoxic and hypobaric environment at high altitudes . Other symptoms like loss of appetite, light-headedness, lassitude, dyspnea and delirium may also be present. Some patients experience worsening of symptoms with the development of either cerebral edema (HACE - high altitude cerebral edema) and/or high altitude pulmonary edema (HAPE). But in a majority of the cases, the symptoms of AMS usually improve after a day unless the patient ascends again to a higher altitude, in which case the symptoms can worsen.
The clinician can diagnose AMS on the basis of the patient's clinical presentation, history, and physical examination findings. History will reveal recent ascent to high altitude by the unacclimatized patient while physical examination may reveal tachycardia, tachypnea, and pulmonary rales if the patient is developing pulmonary edema. Laboratory tests like complete blood count may be abnormal with elevated hematocrit, and erythrocytosis while arterial blood gas analysis will reveal respiratory alkalosis. Pulse oximetry values do not usually indicate the severity of AMS and are therefore not useful in either detecting or in the management of the condition although they may help to detect HAPE. An electrocardiogram may show variable features like right axis deviation, non-specific ST-T changes, sinus arrhythmias, and P wave abnormalities. Chest radiography is indicated only in patients suspected clinically to have HAPE.
The diagnosis and severity of AMS can be assessed using the Lake Louise score (LLS)  as well as the Environmental Symptoms Questionnaire (ESQ)  . The LLS was developed by a consensus conference on Hypoxia and Mountain Medicine in 1991 and consists of a self-reported score which is the sum of responses to five questions  and can be verified by a clinician during an interview. The ESQ consists of an inventory of expected physiological and psychological symptoms and was developed by the United States army. A part of this inventory containing symptoms indicative of cerebral hypoxia (AMS-C) is used to assess AMS . However, the two questionnaires do not corroborate to provide an identical diagnosis  and as yet there is no gold standard tool for the assessment of AMS  .
Despite the presence of AMS symptoms, magnetic resonance imaging does not detect brain edema or an increase in brain volume for up to 12 hours after hypoxia and is therefore not helpful in the diagnosis and management of AMS .