Internal Body Clock Dictates Stroke Onset and Type

IWATE, Japan, Aug. 17 -- Ischemic strokes are more likely to occur in the morning and hemorrhagic strokes in the early evening, according to investigators here.

In an analysis of 12,957 patients who had a cerebral infarction, an intracerebral hemorrhage, or a subarachnoid hemorrhage, researchers found two peaks for onset. One occurred from 6 a.m. to 8 a.m., and the other from 6 p.m. to 8 p.m., with a significant dip during sleep, according to a study published online in the Journal of Neurology, Neurosurgery, and Psychiatry.

The peak in the morning was for cerebral infarction, and the peak in the early evening was for hemorrhagic strokes, said Shinichi Omama, M.D., of Iwate Medical University here, and colleagues.

In an analysis of first-ever stroke diagnosed by brain scan in the Iwate Stroke Registry from 1991 through 1996, the researchers found varying bimodal circadian variations for the three main types of stroke, but in the waking state only.

Subarachnoid hemorrhage was the least common type of event, at 18 per 100,000 of the population per year, while cerebral infarction was the most common with 89 per 100,000 of the population, according to data from the Iwate registry, they reported.

Intracerebral hemorrhage and subarachnoid hemorrhage showed bimodal circadian variations with a lower peak in the morning (6 a.m. to 8 a.m.) and a higher peak in the early evening (6 p.m. to 8 p.m.), whereas cerebral infarction had a single morning peak in all situations at onset.

However, further analysis found that cerebral infarction also had a bimodal pattern with a higher peak in the morning, a small dip around noon, a lower peak in the early evening, and a nadir during the night (P

The results showing similar patterns for intracerebral hemorrhage and subarachnoid hemorrhage indicate similar triggers for these two types. However, other factors are required to explain the difference in the morning and afternoon peaks between ischemic stroke and the two types of hemorrhagic stroke, the investigators said.

Previous studies have pointed to increases in the levels of hematocrit, platelet aggregation, and hypercoagulability in the morning. These factors, the researchers said, promote ischemic events and prevent hemorrhagic events.

Sleep, which lowers blood pressure, cuts the risk of hemorrhagic stroke, but low blood pressure is a risk factor for cerebral infarction, the investigators wrote.

The triggers for stroke onset seem to consist of two types, Dr. Omama said. These are blood pressure, which is common to both ischemic and hemorrhagic stroke and shows a bimodal pattern, and hemostatic functions, which promote ischemic stroke and prevent hemorrhagic stroke in the morning.

In fact, Dr.Omama said, the finding of a bimodal circadian onset of stroke while awake seems useful for further investigation of the triggers for stroke onset.