Identifying the possible risk factors for high-altitude headache in mountaineers

I read with great interest the recent paper by Burtscher et al. (1) identifying the possible risk factors for high-altitude headache in mountaineers. This prospective field-based study undoubtedly provides an insight into some of the risk factors associated with headache at high altitude. However, although not a direct criticism of the current data, some methodological considerations are worth highlighting for future work in this area.

The International Classification of Headache Disorders, 2nd edition (ICHD-II) diagnostic criteria for high-altitude headache are presented in Table 1 (2). Evidence for these criteria is based solely on high-altitude field-based research (3), to which the confounding variables include, but are not limited to, mode and intensity of exercise, food and fluid availability, temperature fluctuations and sleep disturbances, including apnoea. In fact, all these variables are either independent causative risk factors for cephalalgia or triggering factors for at least migraine. Therefore, it is possible that misdiagnosis of previously defined high-altitude headache may explain contradictory characteristics presented in the current criteria (frontal or frontotemporal; dull or pressing), in contrast to those reported elsewhere (global and throbbing/pulsatile-burst (4)). Thus, the exact characteristics of high-altitude headache still remain to be confirmed through well controlled field or laboratory-based studies.

Table 1.

Diagnostic criteria for high-altitude headache as per the International Classification of Headache Disorders: 2nd edition

10.1.1 High-altitude headache
Diagnostic criteria:
A. Headache with at least two of the following characteristics and fulfilling criteria C and D:
1. bilateral
2. frontal or frontotemporal
3. dull or pressing quality
4. mild or moderate intensity
5. aggravated by exertion, movement, straining, coughing or bending
B. Ascent to altitude above 2500 m
C. Headache develops within 24 hours after ascent
D. Headache resolves within 8 hours after descent

Nonetheless, in the current study (1), high-altitude headache was diagnosed by a categorical scoring system (0 to 4), based on headache severity, during the first morning after ascent to high altitude: the defining criterion was a score greater than zero after ascent to high altitude. Consequently, Burtscher and colleagues (1) attribute a variety of headache types related to migraine susceptibility, hypoxia, fluid intake and exertion to ascent to high altitude. In contrast, I suggest that future researchers should attempt to characterize each headache type independently and not simply label all headaches as high-altitude headache just because their presence was reported above sea level. I realize that it is difficult to obtain a detailed description of each person's headache characteristics, particularly in large field-based studies and considering the lack of valid and reliable tools for describing the phenomenology of headache. However, given recent evidence of hypoxia-triggered migraine (5) and the confounding factors presented above, future researchers may consider reporting headache characteristics in addition to severity to properly diagnose headache attributed to high altitude using the ICHD-II criteria. These minor differences in diagnosis may seem superfluous at first, but correct identification of high-altitude headache (reduced barometric pressure and subsequent hypoxia) and not, for example, dehydration- or sleep-apnoea-induced headache maybe of vital importance, especially in uncontrolled field-based studies or when attempting to group subjects by susceptibility and deduce separate causative pathological mechanisms. Finally, although dehydration and exertion can be manipulated at high altitude, as recommended by Burtscher and colleagues (1), the severity of arterial desaturation could also be markedly reduced by the traditional method of slow ascent/acclimatization (6), which is strongly recommended for avoiding illness at altitude.