Acute mountain sickness and the edemas of high altitude: a common pathogenesis?

Within days of ascent to high altitude when symptoms of acute mountain sickness (AMS) are common, pulmonary and cerebral edema may also develop. Although peripheral edema of the hands, face or feet may also appear, its association with AMS is unclear. In addition, persons with high altitude pulmonary edema often report an antidiuresis. Hence, altitude sickness appears to result from abnormalities in the handling of body water. To test this hypothesis, we studied 102 men and women who were trekking in the Mount Everest region of Nepal. Most were seen both at low (1377 m) and at high (4243 m) altitude. Severity of AMS was measured by an established Symptom Score derived from a questionnaire and physical examination. Change in body water was inferred from change in body weight in less than 10 days. Peripheral edema was assessed separately by physical examination. AMS Symptom Score correlated directly with weight change; those who remained well lost weight, whereas increasing signs and symptoms of AMS occurred in those with increasing weight gain. The symptomatic subjects also developed peripheral edema and reported decreased urinary output. These findings support the hypothesis that with rapid ascent to high altitude, abnormalities in the handling of body water, with antidiuresis, result in fluid retention (weight gain) manifest as peripheral, pulmonary, and/or cerebral edema.