Transient increases in the risk of headaches requiring emergency department evaluation are triggered by high ambient temperature and, to a lesser degree, by low barometric pressure, according to a study in the March 10 Neurology.
A total of 7,054 patients (75% women) who were seen at the Beth Israel Deaconess Medical Center (BIDMC) in Boston between May 2000 and December 2007 were assessed in the case-crossover study; 2,250 were discharged with a primary diagnosis of migraine, and 4,803 with tension or unspecified headache. Levels of temperature, barometric pressure, humidity, fine particulate matter, black carbon, and nitrogen and sulfur dioxides from the three 24-hour periods before onset were compared using local meteorologic and pollutant monitors.
Kenneth J. Mukamal, MD, Associate Professor of Medicine at BIDMC, and colleagues, reported a moderate correlation for temperature and relative humidity and a weak correlation between temperature and barometric pressure. Pollutant levels somewhat correlated with each other—most significantly, nitrogen dioxide with sulfur dioxide, and fine particulate matter with black carbon.
“In multivariable models, higher mean ambient temperature in the 24 hours preceding hospital presentation increased the acute risk of headache (odds ratio [OR] for a 5°C increment, 1.075),” Dr. Mukamal’s group stated. The rate of discharge diagnoses increased with temperature for migraine (OR, 1.111), other headache (OR, 1.059), and headaches that occurred in cold (OR, 1.809) and warm months (OR, 1.118). No evidence for a nonlinear effect or effects of temperature in the preceding lag period was observed. Positive results were also observed after considering the minimum and maximum temperatures in the preceding 24 hours (OR, 1.068; OR, 1.039, respectively). “After adjusting for temperature on the 24 hours before hospitalization, there was also no effect of change in temperature in the preceding 24 hours, either in colder or warmer months,” the investigators commented.
Acute risk of headache increased with lower barometric pressure, but only in the 48- to 72-hour period before hospitalization (adjusted OR, 0.939 per 5 mm Hg). Increased risk was only seen in nonmigraine cases (OR, 9.23) and was more significant in colder months. Changes in pressure between 24 and 48 hours before hospitalization did not have any effect in warm or cold months. “There was no association of relative humidity at any lag,” the researchers noted.
A trend toward higher risk with a greater ambient concentration of nitrogen dioxide during the 0- to 24-hour period before hospitalization was observed in cold and warm months (OR, 1.053; OR, 1.062, respectively). No associations were found for any other pollutant. “We did not find a clear association of air pollutants with risk, but cannot exclude effects of air pollution of the magnitude previously observed for stroke and other cardiovascular events,” Dr. Mukamal’s group commented.
An estimated 7.5% higher risk for each 5°C increment in temperature was observed. “This magnitude of excess risk … may not be an important factor in the clinical management of individual patients, given the many other potential triggers of migraine,” Dr. Mukamal and colleagues stated. However, because people are continually exposed to this risk, it may be considered greater than exposures that present a higher relative risk to a smaller number of people.
—Laura Sassano