Dear Editor,
We read with interest the study and we congratulate Algaze et al. (2020) who prospectively assessed the incidence of cognitive impairment with ascending altitude in a large number (103) of trekkers in a relatively standardized way, since low numbers and high variabilities have hampered progress on the issue of cognitive performance (CP) at high altitude in the past. The authors address the important and still underinvestigated topic of reduced CP at altitude considering the practical relevance due to its possible contribution in unexplained accidents. The authors used a slightly modified version of the quick mild cognitive impairment (Qmci) screen, the environmental (eQmci) one (Phillips et al., 2017). They observed a higher incidence (10.7%) at 4300 m compared with 3500 m (3.9%). At 5000 m they observed around the same incidence of cognitive impairment observed at lower altitude (i.e., 3500). Some aspects of the study should, however, be interpreted cautiously. Qmci screen is a modified version of the AB Cognitive Screen 135 (Molloy et al., 2005), where the total score (100) of the original five subtests were reweighted and a subtest added (logical memory). Higher scores (total 70) were attributed to delayed recall, verbal fluency, and logical memory subtests, whereas lower scores (total 30) to orientation, registration, and clock drawing subtests (O'Caoimh et al., 2012). Qmci was developed to distinguish between mild cognitive impairment (MCI) and normal controls, and allows to detect MCI as possible prodrome of dementia, when the amnestic domain is early affected. However, in the setting of high altitude, the acute or chronic exposure to hypobaric hypoxia induces cognitive changes mainly in the domain of attention, executive functions, (working) memory (Malle et al., 2013), and language. Most of these cognitive domains are underestimated with the Qmci and it could result in a lower detection of CI at high altitude. In addition, Algaze et al. used the eQmci removing the clock drawing subtest (given practical concerns of the difficulties to perform it while wearing gloves), and inserted a count backward from 100 by sevens that is a verbal task. The use of such verbal task does not allow to evaluate visuospatial abilities and it is not recommended between two sessions of verbal memory task. An alternative test could have been the Benton Judgment of Line Orientation (although slightly longer). Finally, eQmci has not been validated yet in the population object of the study (even in its original version) and, therefore, caution should be further taken in drawing conclusion.
We think that rather than using a battery that provides a global score with scarce information on a single domain, it would be better to use standardized single tests that assess the specific cognitive domains reported in the literature to be mainly affected with the altitude exposure.
We hope that raising attention to the important topic of CP at altitude will stimulate research and cooperation between neurologists, neuropsychologist, and high-altitude experts to make sojourns at altitude safer and avoid accidents or altitude-related illnesses.
