Clinical features

• acute mountain sickness
  • consists of a constellation of symptoms in the context of a recent gain in altitude
    • symptoms include headache; anorexia, nausea or vomiting; fatigue or weakness; dizziness or lightheadedness; and difficulty sleeping. These non-specific symptoms may be attributed to other conditions, especially by people who are anxious to stick to a preplanned schedule
    • symptoms typically occur six to 12 hours after arrival at a new altitude (but may occur sooner)
      • resolve over one to three days, providing no further ascent is made
  • acute mountain sickness is unusual at altitudes below 2500 metres
  • peripheral oedema may be seen
    • however there are no physical signs that are diagnostic of acute mountain sickness, and the presence of neurological signs should imply the possibility of high altitude cerebral oedema or an alternative cause
      
      
• high altitude cerebral oedema
  • usually preceded by acute mountain sickness and may lead to coma and death
  • prodromal symptoms of early mental impairment or a change in behaviour may be ignored by patients and their companions
  • common symotoms include headache, nausea and vomiting, hallucination, disorientation, and confusion
    • seizures are less common
  • clinical signs include ataxia, a common early feature that may be disabling and is often the last sign to disappear during recovery; a progressive deterioration in concious level, proceeding to coma and death; and papilloedema and retinal haemorrhages
    • focal neurological signs may occur, but in the absence of other signs and symptoms of cerebral oedema these should prompt consideration of other diagnoses
  • severe illness due to high altitude cerebral oedema may develop over a few hours, especially if the prodromal signs are ignored or misinterpreted, and may be accompanied by high altitude pulmonary oedema
  • incidence of high altitude cerebral oedema depends on the speed of ascent and the altitude reached, and is less than 0.001% for people travelling to 2500 metres and approximately 1% for lowlanders travelling to 4000-5000 metres
    
    
• high altitude pulmonary oedema
  • most commonly occurs two to three days after arrival at altitude and consist of dyspnoea with exercise, progressing to dyspnoea at rest, a dry cough, weakness, and poor exercise tolerance
    • as the disease worsens, severe dyspnoea and frank pulmonary oedema are obvious, with coma and death following
  • early clinical signs include tachycardia and tachypnoea, mild pyrexia, basal crepitations, and dependent oedema
  • patients with high altitude pulmonary oedema tend to have lower oxygen saturations than unaffected people at the same altitude
    • however the degree of desaturation by itself is not a reliable sign of high altitude pulmonary oedema
  • high altitude pulmonary oedema rarely occurs below 2500 metres. Its incidence is 0.0001% at 2700 metres, increasing to 2% at 4000 metres
  • speed of ascent, exercise during or immediately after ascent, male sex, youth, and individual susceptibility are all risk factors

Reference:

• 1. Barry PW, Pollard AJ. Altitude illness. BMJ 2003;326:915-919