Abstract
Historical
Paul Bert, in his splendid book La Pression Barometrique (Bert, 1878), devotes the whole of chapter 2, consisting of 155 pages, to accounts of the distress of travelers ascending to high altitude on mountain journeys. It is remarkable how seldom headache is referred to, although there are graphic accounts of gastrointestinal disturbances, extreme fatigue, and dizziness or light-headedness. One example is the famous account of the ascent of Joseph de Acosta in the Peruvian Andes in about 1580 where the principal symptoms were vomiting and extreme weakness. However, Bert recounts the experiences of dozens of other travelers in the 18th and 19th centuries, quoting many of them verbatim. Headache is noted in some accounts, but it is not the dominant symptom in this large series.
Lake Louise Scoring System
The most frequently used standard for the diagnosis of AMS at the present time is the Lake Louise Acute Mountain Sickness Scoring System (Roach et al., 1993). This includes the following statement under the heading Diagnostic Criteria for Acute Mountain Sickness:
A diagnosis of AMS is based on a recent gain in altitude, at least several hours at the new altitude, and the presence of headache and at least one of the following symptoms: gastrointestinal upset (anorexia, nausea, or vomiting), fatigue or weakness, dizziness or light-headedness and difficulty sleeping. A score of three points or greater on the AMS self-report questionnaire alone, or in combination with the Clinical Assessment score, constitutes AMS
This statement is followed by a table giving the five symptom headings.
Headache Gastrointestinal symptoms Fatigue and/or weakness Dizziness/light-headedness Difficulty sleeping
Each of these is graded 0 through 3. The Clinical Assessment score is made by an examiner who examines for changes in mental status, ataxia, and peripheral edema. Finally, there is a Functional Score, which can be self-reported or elicited by the examiner. The question asked is this: Overall, if you had any symptoms, how did they affect your activity? This is graded 0 through 3.
This scoring system was developed by a committee during the Eighth International Hypoxia Symposium in 1993 (Roach et al., 1993), and it was based in part on a previous discussion of criteria for AMS during the Seventh International Hypoxia Symposium in 1991 (Hackett and Oelz, 1992). Another scoring system, which was introduced earlier, is the Environmental Symptoms Questionnaire (ESQ) (Sampson, et al., 1983), which has 67 items and therefore takes longer to complete, although many investigators have used a shortened form. Several studies have shown comparable results for sensitivity and specificity between the Lake Louise and ESQ questionnaires. The ESQ was preceded by the General High Altitude Questionnaire (Evans, 1966), and it is notable that neither it nor the ESQ required headache for the diagnosis of AMS.
Variability of Symptoms among Individuals in Clinical Medicine and at High Altitude
It is well known in clinical medicine that there is often considerable variability among individuals with respect to symptoms accompanying some clinical conditions. For example, most patients with acute appendicitis will complain of abdominal pain, but occasionally this is not present. Similarly, a patient who develops an acute myocardial infarction usually has angina, but again there are exceptions.
The responses of different people to high altitude are notoriously variable. On treks into mountainous regions, some people can reach an altitude of 5000 m with few if any symptoms, whereas others will become incapacitated at half this altitude. Therefore, it seems very bold for the committee who developed the Lake Louise System to insist on one particular symptom for AMS in the light of the great individual variability in clinical medicine.
An Anecdotal Account
Since I became interested in this topic, several people have mentioned that they have occasionally seen people at high altitude who have been seriously affected by some of the symptoms of AMS, but without any headache. Naturally, these are anecdotal accounts. Here is another.
In 2005, part of the VI World Congress of High Altitude Medicine and Physiology was held in Lhasa, altitude 3600 m. We all flew there from Xining, and one of my physiology colleagues became sick on about the second day in Lhasa. His main complaint was severe malaise (his term was “lousy”), and he was markedly incapacitated to the extent that he did not want to leave the hotel room. On repeated questioning, he denied headache. He was so desperate that he tried to inhale oxygen from a dispenser in the room to no effect, and at one stage he went to the emergency room of a Lhasa hospital for a chest X-ray because he had a dry cough. The radiograph was normal. But the most striking feature of his illness was that while he remained very unwell during the whole of his stay in Lhasa, as soon as he flew to a lower altitude he completely recovered within a period of minutes. This seems to be strong evidence that his illness was caused by the altitude, but it certainly did not fit the Lake Louise criteria for AMS.
A Different Set of Diagnostic Criteria for High Altitude Diseases from China
In 1996, a committee in China published an article titled Nomenclature, Classification, and Diagnostic Criteria of High Altitude Disease in China. This was essentially unknown outside China until a translation was recently published in High Altitude Medicine & Biology (West, 2010). Because these guidelines were developed 14 years ago, many physicians in China now use the Lake Louise criteria, which were described above. However, some continue to use the 1996 guidelines, and these are of interest. They cover not only AMS, but also high altitude pulmonary edema (HAPE), high altitude cerebral edema (HACE), and chronic diseases such as chronic mountain sickness (CMS).
The name given to AMS was acute mild high altitude disease (AMHAD) to distinguish it from the chronic diseases including CMS and the more severe diseases such as HAPE and HACE. Table 1 of that publication gives a long list of symptoms relevant to AMHAD, including headache, vomiting, dizziness/light-headedness, nausea, palpitations, shortness of breath, chest distress, dazzling/blurred vision, sleeplessness, anorexia, abdominal distention, diarrhea, constipation, cyanosis of the lips, lethargy, and numbness of the extremities. Headache scored 1 to 7 points based on its severity, vomiting scored 2 to 7 points, and all the other symptoms and signs scored 1 point each. Mild AMHAD was diagnosed when the presence of headache or vomiting affected the functioning of daily activities or, if neither of these symptoms was present, a score of 5 to 10 based on the other symptoms was required. The severity of AMHAD was reported as mild, moderate, or severe.
A Large Study of Mountain Sickness Using the 1996 Chinese Criteria
The 1996 Chinese criteria were used by Ren and colleagues (2010) to study the incidence of high altitude illnesses in 3628 male army recruits aged 16 to 22 yr who were airlifted from near sea level to Tibet at an altitude of 3600 m. The authors reported that 57% had mild AMHAD, which in the manuscript they called AMS although they were not using the Lake Louise criteria. Twelve percent of the subjects with AMHAD were hospitalized for treatment. The incidence of HAPE was only 1.9%, and there were no cases of HACE.
The high incidence of mild AMS was remarked on by one of the reviewers of the manuscript and prompted our search for the diagnostic criteria. These were subsequently translated and published, as indicated above. The fact that headache was not required for the diagnosis of AMS was presumably part of the reason why the incidence of AMS was so high. The results of this very large study suggest that more people who acutely ascend to 3600 m develop high altitude illnesses according to the Chinese criteria than would be picked up by the Lake Louise Score for AMS.
Conclusion
The main conclusion from this preceding discussion is that more people suffer from the deleterious effects of acute ascent to high altitude than are picked up by the Lake Louise criteria for AMS. It seems reasonable to suggest that requiring headache as a symptom for the diagnosis of AMS is to some extent an arbitrary cutoff point. Certainly, in some cases, for example in the anecdotal example given previously, some subjects are severely affected by the ascent and yet do not complain of headache.
Should any change be made in our diagnostic criteria? It could be argued that a large number of publications are based on the Lake Louise scoring system, and it would be confusing to change the criteria at this stage. However, one possibility would be to add another category, perhaps symptoms of acute mountain sickness and abbreviate this as SAMS or simply SMS. This would refer to people who have some clearly defined symptoms as a result of the acute ascent, but do not meet the Lake Louise criteria of AMS. Possibly, the basic Lake Louise procedure could be used without the requirement that headache be essential. Or perhaps a broader set of criteria could be developed incorporating the Lake Louise, ESQ, and Chinese recommendations.