ALTITUDE AND COMMON MEDICAL CONDITIONS - Medicine for Mountaineering and Other Wilderness Activities - page 374

The important question of whether high altitude aggravates migraine has not received
sufficientattention.ThattheheadacheofAMSandthatofcommonmigrainemaybenearly
indistinguishable presents obvious problems in diagnosis and determination of incidence.
The mechanisms for migraine and the headache of AMS could be similar. To test this hy-
pothesis, sumatriptin, a drug (5HT 1 -receptor agonist) effective for migraine, was evaluated
as therapy for the headache of AMS. The results were mixed, and further study is required.
One population in which migraine is easier to identify at altitude is the high-altitude
native, a population that does not suffer from AMS. When Peruvian high-altitude natives
were compared tolowlanders, 12.4percent ofageneral population at 14,200feet (4300m)
suffered migraine headaches, but only 3.6 percent of a similar population at sea level had
that problem.
In a group of 379 adult men subsequently studied at 14,200 feet (4300 m) by the same
investigators, the incidence of migraine headaches was 32.2 percent and correlated with
increasing age, hemoglobin values, and chronic mountain sickness. For all types of head-
aches the incidence was 54.6 percent, far higher than reported in Peruvian and other popu-
lations living at low altitude. The authors postulated that migraine in this population might
be higher due to the combined effects of hypoxia, polycythemia, and reduced cerebral
blood flow. Since migraine in this population may be related to chronic mountain sickness,
adisorderthatdevelopsoveraperiodofyears,theimplicationsforhigh-altitudesojourners
are unclear.
Whether ascent to high altitude increases the frequency orseverity ofheadaches in low-
landers with migraine is not yet determined, but clearly ascent can trigger migraine in both
those with and those without a prior history of migraine at sea level. In one study, mi-
graine developed repeatedly in susceptible individuals during simulated altitude exposure
between 9000 and 11,000 feet (2750 and 3400 m). For others, although frequency may re-
main stable, the severity may change. Migraine must be included in the differential dia-
gnosis of a severe headache at altitude, even with apparent AMS, particularly when asso-
ciated with visual or other focal neurologic deficits. Whether hypoxic gas breathing at sea
level can identify individuals in whom high altitude may trigger an attack has not been in-
vestigated.
STROKE, TIA, CEREBROVASCULAR DISORDERS, AND ALTITUDE
Whether the incidence or severity of cerebrovascular disease (CVD) and stroke is different
in highaltitude natives than in sea-level populations is unclear. Surveys conducted in rural
areasofSouthAmericaandAsiaoverarangeof5100to14,200feet(1550to4300m)have
suggested a lower incidence of CVD. However, an epidemiological study reported that the
prevalence ratio for CVD at 11,200 feet (3400 m) in Peru was close to the worldwide aver-
age. Discerning the true relationship between altitude and cerebrovascular disease requires