NASHVILLE—Measuring optic nerve sheath size using noninvasive optic ultrasound may help clinicians identify patients at increased risk of death after acute stroke, according to research presented at the 2015 International Stroke Conference. The diameter of the optic nerve sheath changes with increased intracranial pressure, which may suggest greater stroke severity and result in death.
Deterioration on the neurologic exam is an early indicator of increasing intracranial pressure, but confounding factors (eg, fluctuations in mental status and sedation or paralysis resulting from acute management) limit the exam’s accuracy at detecting this symptom. “Ultrasound on the optic nerve can be used to test [the] brain for swelling, which sometimes occurs after a major stroke,” said Vishnumurthy Shushrutha Hedna, MD, Assistant Professor of Neurology at the University of Florida in Gainesville. “It is thought that when [the] brain swells, pressure gets transmitted towards [the] eyes. This [test] would help doctors treat … stroke with medications that would reduce brain pressures.”
Larger Measurements Among Patients Who Died
At a tertiary care center, Dr. Hedna and colleagues prospectively studied 86 patients with stroke whom they suspected of having elevated intracranial pressure. The investigators performed optic ultrasound on the day of admission and on the following day at each participant’s bedside to measure optic nerve sheath diameter (ONSD). The researchers took a longitudinal and a transverse measurement on each eye of each patient. Data analysis included paired t tests and χ2 to compare measurement means and proportions. In addition, Dr. Hedna’s group conducted regression analysis to assess relationships between ONSD and patient outcome.
Among participants with ischemic stroke, mean ONSD was significantly different between patients who died, compared with patients who survived (0.582 cm vs 0.533 cm). The researchers also found a significant difference in mean ONSD between people with intracerebral hemorrhage who died, compared with people with intracerebral hemorrhage who survived (0.623 cm vs 0.572 cm).
Overall, for every 0.1-cm increase in ONSD, the odds of mortality were 4.239 times higher than the odds of survival among patients with ischemic stroke. For every 0.1-cm increase in ONSD among patients with intracerebral hemorrhage, the odds of mortality were 6.222 times higher than the odds of survival. Most of the deaths occurred within one month of hospitalization. In addition, increased ONSD measurements had a moderately strong correlation with poorer modified Rankin Scale scores at six months.
Test Should Be Administered Quickly
Increased ONSD measurements correlated with poor short-term (ie, in-hospital) and long-term (ie, at six months) mortality. “Optical ultrasound may be used as a screening tool to identify patients at risk of poor outcome from increased intracranial pressure,” said Dr. Hedna. In the future, the technique may enable treating physicians to initiate early therapeutics to improve patient care.
The ultrasound test is likely to be useful in stroke care only when administered soon after stroke injury, said Dr. Hedna. “Brain swelling after stroke usually peaks [at] between three to four days, hence its use in the acute stroke setting.”
The investigators are studying whether differences in ONSD from day one to day two are related to patients’ risk of death or disability. They plan to study whether treating patients for fluid buildup on the brain based on an abnormal neurologic exam plus a bigger nerve sheath affects their outcomes, compared with standard care. The most severely impaired patients “are probably the ones who would get medications to decrease brain edema later in the course of their illness anyway,” said Dr. Hedna. “The ONSD would help the clinician make the decision sooner.”
—Erik Greb
