How long blood transfusions are needed to optimize stroke reduction and minimize transfusion-related problems in children with sickle cell disease is the focus of a new, federally funded study of 100 children at 20 sites across North America.
"We know that regular blood transfusions decrease these children's stroke risk by 90 percent," said Dr. Robert J. Adams, neurologist at the Medical College of Georgia and principal investigator on the $11 million study funded by the National Heart, Lung and Blood Institute. "Now we need to determine the optimal amount of time these children need transfusions."
Participants in the Optimizing Primary Stroke Prevention in Children with Sickle Cell Anemia, or STOP II, study have been receiving monthly transfusions for several years and many have moved into a low-risk category based on regular blood flow studies of their brains.
Half of these children will continue to receive transfusions over the next two to four years; the remainder will no longer get transfusions but will be monitored closely with transcranial Doppler, which uses ultrasound to measure blood flow in the brain.
"Finding the optimal amount of time transfusions are needed to reduce stroke risk is a very logical next step," said Dr. Virgil C. McKie, chief of the MCG Section of Pediatric Hematology/Oncology, director of the pediatric sickle cell clinic at the MCG Children's Medical Center and co-investigator on the STOP II study.
Transfusions benefit these children in several ways, but not without costs, including a potentially harmful buildup of iron that is common after two to three years of monthly transfusions and an immune response that eventually can hinder finding suitable blood donors, Dr. McKie said.
The original $12.1 million STOP study, which identified the 90 percent reduction in stroke risk, began in early 1995 and followed 130 at-risk children with sickle cell disease ages 2-16 at 14 sites in the United States and Canada; half the children received transfusions and the remainder received standard care.
Federal health officials halted the original STOP study 16 months early, in September 1997, because of the obvious benefit of transfusions to children at high risk. And the NHLBI issued a physician advisory recommending regular transcranial Doppler studies in children ages 2-16 with sickle cell disease and consideration of transfusions in children found to be at risk.
As researchers followed the vascular disease progression in these children, they found that most of those receiving transfusions not only were stroke-free but actually began to have normal transcranial Doppler studies.
Categorizations of blood flow rates include a normal rate of 170 centimeters or less per second and 170-199 centimeters per second, which is conditional and prompts close observation with repeated transcranial Doppler studies. Children with rates of 200 or greater are considered at high risk and clearly benefit from transfusions, Dr. Adams said. The increased speeds reflect a narrowing of the blood vessel and potential stroke site. Magnetic resonance angiography was later added to provide images of suspect areas.
Researchers are not certain why the risk decreased in some children. It could be a number of factors including the growing size of the child and his blood vessels; possibly a childhood infection triggered the original problem. It's been observed that the stroke risk naturally tends to decline in early adulthood, he said.
"Transcranial Doppler is sensitive enough that many of the patients determined at risk had disease that was still at an early stage and reversible," Dr. Adams said. "But if we take those patients who already had severe lesions on magnetic resonance angiography, those kids were unlikely to drop into the normal range with transfusion."
What isn't known conclusively is why some children move from high-risk to low- or conditional-risk and if the improvement holds up after transfusions are stopped. "Does a low-risk transcranial Doppler after 30 months of transfusion mean the same thing as a child who was never at risk?" Dr. Adams said.
He hopes to answer those questions with the new study. "We will be taking children off transfusion whose Dopplers have improved and whose magnetic resonance angiograms look reasonably normal," Dr. Adams said. "These are the kids who we think have been caught as they entered into this risk domain, but they have not been allowed to stay there long enough to really damage their vessels. If we can demonstrate that a substantial number of these patients do not go back up in stroke risk, then we can reduce the toxicity and costs of transfusion and still get stroke prevention.
"Our eventual goal and hope is that with early and frequent transcranial Doppler studies and other testing coupled with targeted, relatively short-term intervention, the severe vessel damage that leads to stroke, resulting disability and even death in some cases, can be prevented in children," Dr. Adams said.
About 1 in 10 children with sickle cell disease are at risk for stroke; the peak risk period is the formative years when developing brains experience a peak demand for blood and oxygen, Dr. Adams said.
Blood transfusions have been used for years to avoid a second stroke in children with sickle cell disease and for sickle cell patients of all ages who experiences pain crises, low hemoglobin counts and other manifestations of the disease.
Drs. Adams and McKie, published a paper in the New England Journal of Medicine in 1992 that identified the painless transcranial Doppler as the first non-invasive method for identifying these children before their first stroke.