This study compared the outcomes of two scoring criteria (the Lake Louise Score (LLS; score of ≥ 3) and the Chinese AMS Score (CAS; score of ≥ 5)) on the assessment of AMS in a large group including a total of 2486 subjects who rapidly entered a high-altitude area (3658 m) by plane. To the best of our knowledge, this is the first large-sample study on the incidence of AMS as determined by the LLS and CAS diagnostic criteria. The CAS had testing characteristics for diagnosing AMS similar to those of the LLS and showed a generally consistent trend with the LLS, and the CAS diagnosed a higher prevalence of AMS than the LLS criteria did.
The results of this study show that the incidence of AMS diagnosed by the LLS and CAS was 37.5% and 59.3%, respectively. In studies that used an airplane approach, Harrison et al.[23] reported an AMS incidence of 33.3% using the LLS criteria, and Ren et al.[24] reported an AMS incidence of 57.2% using the standard CAS; our results are consistent with both of theirs. Because AMS evaluation lacks reliable biomarkers and clinical indicators, it mainly depends on the determination of some neurological, gastrointestinal and respiratory symptoms at high altitude. Both the CAS and LLS were evaluated by symptomatology scoring in a similar way. However, due to the different symptoms and weights assigned, the incidence determined by the CAS assessment was higher than that by the LLS (59.3% vs 37.5%). This was consistent with previous studies[8, 9]. The CAS had diagnostic accuracy for moderate and severe AMS similar to those of the LLS (16.9% vs 17.2%). However, the difference was significant for mild AMS (42.3% vs 20.3%).
To help improve the AMS diagnostic criteria, some scholars compared and evaluated the different scoring criteria. [25] [26] [27] [11] Some Chinese scholars have studied the difference between the LLS and CAS in defining AMS. Chen et al.[9] surveyed 339 males residing at sea level who travelled by train and car to 3200 m. Wu et al.[8] surveyed 58 males who went by train and recorded the AMS incidence when they reached different altitude sites, ending at 3658 m. They found that CAS outcomes were in good agreement with LLS outcomes and can accurately diagnose AMS, suggesting that combining the LLS and the CAS in applications of clinical diagnosis can more objectively diagnose AMS than one scoring system alone.
The LLS and CAS are self-report questionnaires that diagnose AMS using a subject's self-assessment of symptom intensity. The two scoring criteria have different scoring rules, resulting in different diagnostic results[20]. The LLS highlights the importance of headache as the main criterion for the diagnosis of AMS and demands the presence of headache, and a total score of 3 or more can diagnose AMS. It is generally believed that acute mountain sickness is associated with high-altitude cerebral oedema and that this pathophysiological process should be explored. It is believed that the vasodilation caused by hypoxia or its effectors may cause headache by activating the trigeminovascular system[28]. An alternative hypothesis is that early AMS is caused by mild high-altitude cerebral oedema[29]. AMS is the pathogenetic precursor to high-altitude cerebral oedema.
However, there are ongoing controversies about whether headache is a necessary criterion for the diagnosis of AMS[22, 30]. The CAS criteria mainly emphasize headache and vomiting, which are major but nonspecific symptoms in the diagnosis of AMS, and the weight of headache is still very high. According to the severity, whether a symptom affects activity ability and general drug treatment response, weight scores of 1, 2, 4, and 7 are given. Even if subjects do not have headache or vomiting but merely have a total score of 5 or more, they could also be diagnosed with AMS. In this study, 541 subjects were diagnosed with AMS by the CAS, while they were diagnosed as AMS negative by the LLS. Although they had mild AMS as determined by the CAS and may not have progressed to life-threatening pulmonary and cerebral oedema, these people were still troubled by many typical symptoms (such as headache, vomiting, chest tightness, shortness of breath, etc.). Because there was no headache (214, 39.6%) or only headache and the total score of less than 3 (327, 60.4%), AMS could not be diagnosed by the LLS. For example, four subjects with severe gastrointestinal symptoms were diagnosed with severe AMS by the CAS but were considered to not have AMS by the LLS due to no headache. This observation is in line with a new view of AMS: AMS might not be a single syndrome but may manifest in different ways and present as symptom clusters that vary between patients, such as headache, headache and sleep disorders, fatigue and respiratory symptoms, and gastrointestinal symptom clusters[5, 31]. Therefore, whether headache should be a necessary item in the diagnosis of AMS and the difference in pathophysiological mechanisms between atypical manifestations without headache and typical AMS need further research and discussion. If we want to improve the AMS diagnostic criteria to achieve the desired diagnostic ability, we should consider a small number of people who have no headache but have more overall discomfort. It is beneficial for medical interventions to define them as AMS patients.
The LLS includes five independently assessed symptoms, while the CAS includes more than ten other types of symptoms, such as palpitation, chest tightness and shortness of breath, which are scored as 0 or 1 point. It is simpler to use the LLS to make diagnoses on the plateau, as it is conducive to rapidly diagnose patients. The CAS diagnostic criteria are more extensive but also increase the complexity of diagnosis. For example, the CAS takes into account the judgement-biasing effect of conventional drugs, while the LLS depends only on the subjective feelings of the participants. The additional symptoms included in the CAS can help medical staff to find more unadaptable people in time and to initiate appropriate treatment to alleviate the further development of symptoms.
The influence of high altitude on organisms involves nearly every organ system. However, the LLS did not include the symptoms of the effects of hypoxia on the respiratory system because scholars considered the primary significance of AMS to be its potential for progression to HACE.[32] However, high-altitude pulmonary edema (HAPE) is also a high-altitude illness with an incidence rate of approximately 0.1%. HAPE that is ignored or unrecognized may pass rapidly through a stage of dyspnoea and progress overnight to severe encephalopathy and coma[32]. According to the survey results, the incidence of chest distress was 40.4%, ranking fourth among symptoms, and the incidence of shortness of breath was 37.2%, ranking fifth among symptoms, both of which are symptoms of the influence of a hypoxic environment on the respiratory system. The cluster analysis results also confirmed this point; shortness of breath and chest distress were relatively independent of the five symptoms on the LLS. Therefore, it is suggested that the two symptoms involved in the CAS should be included in the scoring system in future revisions of the standard. This helps AMS diagnostic instruments identify more potential patients and provide timely medical services to improve the living comfort and mobility of patients. The AMS diagnostic criteria have been continuously improving[20]. To better diagnosis and study AMS, we hope that our research can provide some help for the improvement of AMS scoring criteria.
Although this study had a large sample size, the participants were all young men, preventing generalizations from our sample to women and other age groups. The monitoring index was simple, as it only analysed and compared the main indexes and scores for AMS, but physiological indexes, such as pulse, blood pressure or blood oxygen saturation, were not recorded.