Ultrasound reveals sickle-cell stroke risk.

Ultrasound reveals sickle-cell stroke risk

A new ultrasound method may help identify children and teenagers with sickle cell anemia who run a high risk of stroke, alerting physicians in time to begin preventive treatment.

Sickle cell anemia is a genetic disorder in which the normally round, puffy red blood cells contain defective oxygen-carrying molecules and sometimes become rigid and crescent-shaped. The disease causes frequent painful episodes when the distorted red blood cells block blood flow through tiny capillaries.

But an even greater threat lurks for sickle-celled children and teens if the arteries carrying blood to the brain become narrowed with a buildup of scar tissue. Researchers don't know what triggers the deposits, but they do know that these youngsters risk suffering a stroke -- which can cause potentially lethal brain damage -- when their abnormal red cells pile up in the already narrowed arteries, reducing the blood flow to the brain.

Physicians caring for sickle cell patients have had no way to tell which individuals possessed this added vulnerability until after signs of blood-flow restriction appeared. By that time, irreversible brain damage may already have occurred. Strokes can cause mental retardation, paralysis, coma and even death.

Scientists at the Medical College of Georgia in Augusta have now developed an ultrasound method, called transcranial Doppler, that uses sound waves to gauge the speed of blood flow to the brain. Neurologist Robert J. Adams and his colleagues reasoned that blood would travel at a higher velocity in narrowed arteries than in healthy ones, providing an early warning of impending stroke.

Their preliminary findings suggest the technique holds promise as a screening tool, Adams reported last week at the American Heart Association's annual science writers forum in Savannah, Ga. His team studied 250 children and teens with sickle cell anemia, using transcranial Dopper imaging to identify 40 individuals with higher-than-normal blood velocities (more than 160 centimeters per second). Six patients in that high-risk group suffered strokes within months of the ultrasound test, while only one stroke occurred among the 210 children with normal blood velocities, Adams says, suggesting that blood velocity can indeed foreshadow vessel occlusion.

The team then focused on seven of the youngsters who showed no discernible symptoms of stroke but whose ultrasound tests had indicated abnormally high blood velocities. Adams says such children may experience slight reductions in blood flow to the brain, which could lead to subtle brain damage that goes undetected during clinical examination. Using a magnetic resonance imaging device to visualize damaged tissue, the researchers discovered abnormal brain areas in three of the seven, whereas a group of 17 other youngsters who had normal ultrasound test values showed no brain injuries in the same type of images. Only further research will tell whether the three with brain abnormalities had suffered a "silent stroke," Adams says.

"This test may predict [sickle cell] patients at risk for stroke," says neurologist Steven G. Pavlakis at the Cornell University Medical College in New York City. If additional evidence confirms its predictive power, physicians might reduce these children's stroke threat by giving them blood transfusions every three to four weeks, he adds. Such transfusions would help prevent stroke by substituting normal blood cells for the sickling cells, Pavlakis says.

It's unclear whether the ultrasound method can uncover stroke jeopardy in a wider population, says John R. Marler at the National Institute of Neurological Disorders and Stroke in Bethesda, Md. Adams says he believes the technique holds promise for detecting stroke risk in the general population, but agrees that additional studies must establish its range of usefulness.