Age and Acute Mountain Sickness: Examining the Data

To the Editor: Conventional wisdom holds that advanced age is protective against acute mountain sickness (AMS). This concept has been repeated in several recent literature reviews.1,2 It is counterintuitive that older patients, with less physiological reserve and more comorbidities, would be less susceptible to AMS. With this in mind, the data leading to the notion that age is protective against AMS was reviewed. Illness induced by altitude exposure occurs in three forms: AMS, high-altitude cerebral edema (HACE), and high-altitude pulmonary edema (HAPE). AMS is defined as the presence of headache and at least one of the following: gastrointestinal distress, fatigue, dizziness, lightheadedness, or sleep disturbances in a person exposed to recent significant altitude gain. HACE is defined as altered mental status or ataxia in a person with AMS or the presence of altered mental status and ataxia in a person without AMS. HACE is on a continuum with AMS and is considered to be severe or end-stage AMS.3,4 HAPE is currently understood to be an entity independent of AMS and HACE. A 1976 study of tourist trekkers in Nepal reported an inverse relationship between age and AMS. In this study, AMS was diagnosed using a nonstandard symptom-based point scale and a physical examination of some but not all subjects. Of 278 tourists, 53% developed AMS according to these nonstandard criteria. The average age of those with AMS was 31.4 (range 18–62), and the age of those without AMS was 35.2 (range 19–71). Although this 3.8-year difference between the mean values was statistically significant, the incidence of AMS in older individuals and the severity of AMS stratified by age were not described.5 A larger 1993 study also found an inverse relationship between age and AMS in a convenience sample of visitors to Colorado resorts. Of 3,158 individuals, 25% developed AMS according to a standardized diagnostic scale. In those aged 60 and older, the incidence was 16%.6 Another report studied the 50th reunion of the U.S. Army's 10th Mountain Division, based in Leadville, Colorado, during World War II. Of 97 individuals aged 59 to 83, AMS incidence was 16% using standardized contemporary criteria. Using historical controls, the authors reported consistency with the above data.7 A more recent methodologically sound study reported no relationship between age and AMS incidence.8 The quantity and quality of data are insufficient to conclude that advancing age confers protection against AMS. Earlier studies used varying definitions of AMS. Contemporary standardized definitions for altitude-related syndromes are now available.4 Studies using these definitions are of higher quality but are weakened by the use of historical controls that used other diagnostic criteria. A paucity of data on comorbid conditions, fitness, and physiological reserve further impairs meaningful interpretation. In older individuals, it is possible that the nonspecific symptoms of AMS were attributed to comorbid conditions, thus leading to underdiagnosis of AMS in this population. Studies have also primarily assessed tourists of European descent, excluding other populations exposed to altitude such as pilgrims and local people employed in the tourist industry. Thus, the statistically significant differences in average age between those who are and are not affected AMS may be a reflection of bias and methodological flaws rather than a true resistance to AMS with advancing age. Older visitors to higher altitudes are likely to become more heterogeneous as the population ages and the global adventure travel industry expands. Counseling patients using current data could lead clinicians and travel personnel to underestimate the risk of AMS in an at-risk population. Thus the relationship between AMS and age should be rigorously studied. Further studies of AMS should employ standardized diagnostic definitions, prospectively defined endpoints and age ranges, evaluations of fitness, comorbidities, concomitant medications, acclimatization, and rate of ascent. Until such information is available, we should refrain from disseminating the notion that age is protective against AMS.