The 2018 Lake Louise Acute Mountain Sickness Score

Acute mountain sickness (AMS) is the most common form of acute altitude illness and typically occurs in unacclimatized persons ascending to altitudes >2500 m, although it can develop at lower altitudes in highly susceptible individuals. Established risk factors include rate of ascent, altitude reached, and individual predisposition. With 25 years of use in hundreds of publications, the Lake Louise AMS score has provided a robust and practical tool for researchers to diagnose and to score the severity of AMS. Recent opinion (Milledge, 2014) and research (MacInnis et al., 2013; Hall et al., 2014) have suggested that updating the Lake Louise AMS score is in order. This article outlines the brief historical background, reviews diagnostic criteria, describes modifications to the score, and offers suggested experimental procedures that may improve the use of the score in future studies.

At the 1991 International Hypoxia Symposium, the participants executed a consensus process chaired by Peter Hackett and Oswald Oelz (Hackett et al., 1992; supplementary reprint of original article is available online at www.liebertpub.com/ham) to define and quantify the various altitude illnesses. Subsequently at the 1993 conference, all delegates were given the opportunity to have input into the preparation of the document. The score for AMS consisted of the five symptoms (headache, gastrointestinal upset, fatigue/weakness, dizziness/light-headedness, and sleep disturbance), rated on a scale of severity from 0 to 3. The double-worded terms were to facilitate understanding as well as translation into many languages (Roach et al., 1993; supplementary reprint of original article is available online at www.liebertpub.com/ham). A total score ≥3, in the presence of a headache, was considered diagnostic for AMS.

This effort is the result of online discussions and meetings at the International Society of Mountain Medicine World Congress in Bolzano, Italy, in May 2014 and at the International Hypoxia Symposium in Lake Louise, Canada, in February 2015. Members of the consensus committee are those who have participated in the online or in-person discussions and are listed in alphabetical order in the box.

Although use of the scoring system has helped standardize the diagnosis and severity of AMS across research studies, debate has persisted since its inception regarding whether sleep should be included in the diagnostic criteria. Recently this discussion has intensified. Two independent reports in 2013 provided empirical evidence that sleep disturbance is discordant from other symptoms of AMS (MacInnis et al., 2013; Hall et al., 2014). Hall et al. (2014) used network analysis of data from 292 research volunteers exposed to altitudes from 3650 to 5200 m to demonstrate that sleep disturbance correlated poorly with other symptoms of AMS. Importantly, sleep disturbance was absent in 40% of cases with severe headache, long considered a hallmark of AMS. MacInnis et al. (2013) applied factor analysis to Lake Louise AMS scores of 491 Nepalese pilgrims at 4390 m and revealed that sleep had only a weak relationship with the other four symptoms in the score. Milledge also expressed doubt as to whether sleep disturbance was a symptom of AMS, or rather an effect of hypoxia per se, based on his own experience with AMS studies (Milledge, 2014). Another problem recognized over time is that many studies of AMS have used only daytime exposures, making the sleep component irrelevant. Without a score for sleep in these studies, comparison with overnight studies is difficult. Based on these concerns, the consensus committee recommends that the sleep component be removed from the Lake Louise AMS score.

AMS is defined as a Lake Louise AMS score total of three or more points from the four rated symptoms, including at least one point from headache in the setting of a recent ascent or gain in altitude (Roach et al., 2011; West, 2011) (Table 1). Some authors have suggested a higher cutoff for diagnosing AMS (Maggiorini et al., 1998; Bärtsch et al., 2004), but the consensus committee believes that by eliminating the sleep question, more people with true AMS will be identified at the threshold of three points, including headache. Sufficient research is lacking to divide the score into severity rankings. For those who wish to do so, we suggest mild AMS as 3–5 points, moderate AMS as 6–9 points, and severe AMS as 10–12 points. Although symptoms can develop within 6 hours of gain in altitude, we recommend assessing AMS score only after 6 hours, to avoid confusing AMS with confounding symptoms from travel or responses to acute hypoxia (e.g., vagal responses). If investigators wish to assess the impact of AMS symptoms on overall function at high altitude, the “AMS Clinical Functional Score” is available (Table 1).

AMS must not be confused with high-altitude cerebral edema (HACE). AMS alone exhibits no neurological findings, and is self-limited. In contrast, HACE, which usually comes on between 24 and 72 hours after a gain in altitude, is characterized by change in mental status and/or ataxia, occurs usually in a person with AMS or high-altitude pulmonary edema, and is a medical emergency (Hackett and Roach, 2004; Willmann et al., 2014).

This Lake Louise AMS score is for use by investigators studying AMS. It is not intended for use by clinicians, professional outdoor guides, and laypersons to diagnose or manage AMS. After a recent gain in altitude or induction of hypoxia, and an exposure of at least 6 hours duration, the AMS score is used as follows:

Further research should focus on the following areas: (1) best methods for Lake Louise AMS score administration; that is, is investigator-led scoring different/better than volunteer-completed scores? (2) the impact of experimental design, the testing environment, and expectations of research volunteers (i.e., nocebo) (Benedetti et al., 2014) on reliability of Lake Louise AMS score; (3) the clinical and functional impact(s) of AMS score severity; (4) best practices for use of the Lake Louise AMS score and clinical functional score by nonexpert clinicians, mountain guides, and laypersons (Roach et al., 1993; supplementary reprint of original article is available online at www.liebertpub.com/ham; Meier et al., 2017); (5) the impact of disturbed sleep on overall well-being at high altitude, independent of AMS; and (6) the pathophysiology of typical AMS vs. presentation without headache (Roach et al., 2011; West, 2011). In addition, we strongly encourage researchers to publish all individual scores for all volunteers and all symptoms. This will allow other researchers to directly compare patterns of illness, to compile meta-analyses, and to examine the raw data for ideas and observations that will further refine the consensus definition and scoring of AMS.