Network analysis reveals distinct clinical syndromes underlying acute mountain sickness

TL;DR

This study uses a data-driven approach to analyze symptoms of acute mountain sickness, revealing that AMS comprises at least two distinct syndromes rather than a single disease entity.

Contribution

It introduces a novel, unbiased method to explore AMS symptomatology, challenging the traditional view of AMS as a single syndrome by identifying distinct symptom patterns.

Findings

Sleep disturbance and fatigue often occur together, but not always with headache.

Severe headache can occur without sleep disturbance in AMS.

Symptoms of AMS form at least two distinct syndromes, not a single disease process.

Abstract

Acute mountain sickness (AMS) is a common problem among visitors at high altitude, and may progress to life-threatening pulmonary and cerebral oedema in a minority of cases. International consensus defines AMS as a constellation of subjective, non-specific symptoms. Specifically, headache, sleep disturbance, fatigue and dizziness are given equal diagnostic weighting. Different pathophysiological mechanisms are now thought to underlie headache and sleep disturbance during acute exposure to high altitude. Hence, these symptoms may not belong together as a single syndrome. Using a novel visual analogue scale (VAS), we sought to undertake a systematic exploration of the symptomatology of AMS using an unbiased, data-driven approach originally designed for analysis of gene expression. Symptom scores were collected from 293 subjects during 1110 subject-days at altitudes between 3650m and 5200m on Apex expeditions to Bolivia and Kilimanjaro. Three distinct patterns of symptoms were consistently identified. Although fatigue is a ubiquitous finding, sleep disturbance and headache are each commonly reported without the other. The commonest pattern of symptoms was sleep disturbance and fatigue, with little or no headache. In subjects reporting severe headache, 40% did not report sleep disturbance. Sleep disturbance correlates poorly with other symptoms of AMS (Pearson r = 0.31 vs headache). These results challenge the accepted paradigm that AMS is a single disease process and describe at least two distinct syndromes following acute ascent to high altitude. This approach to analysing symptom patterns has potential utility in other clinical syndromes.