Clinical features of headache at altitude: a prospective study.

BACKGROUND: Headache is the most common nervous system complication at altitude; however, there have been few attempts to characterize clinical features of high-altitude headaches (HAH). OBJECTIVE: To measure prospectively the incidence of HAH and to determine its risk factors and characteristics. METHODS: Members of an expedition to Kanchenjunga base camp in Nepal (5,100 m) were prospectively studied. Subjects were interviewed prior to the trip and while trekking recorded headaches experienced at >3,000 m using a structured questionnaire incorporating International Headache Society (IHS) and acute mountain sickness (AMS) criteria. In addition, clinical features of headaches in 19 trekkers in other groups above 3,000 m were recorded using the same questionnaire. RESULTS: Eighty-three percent (50/60) reported at least 1 HAH (median 2, range 0 to 10). Those who developed HAH were younger (p = 0.04); women and persons with headaches in daily life were more likely to report severe headaches (p = 0.03 and p = 0.07). One hundred thirty-eight HAH, experienced by 69 persons, are described. The mean altitude at which headaches occurred was 4,723 m. Twenty-six percent of headaches woke subjects at night or occurred upon awakening. HAH reported by migraineurs were accompanied by more phonophobia (p = 0.008). There were no IHS accompanying symptoms in 44% of headaches or symptoms of AMS in 52% of headaches. CONCLUSIONS: Headaches are a frequent complication of ascent to altitude. Older age appears to offer some protection, whereas headaches were more severe in women and persons with headaches in daily life. There is a wide clinical spectrum, with some suggesting intracranial hypertension. There is a need for evidence-based diagnostic criteria for headaches at altitude.