Stroke, defined as an acute, clinically apparent neurological event, occurs in 8-11% of children with Hb SS. Most strokes are ischemic events caused by stenosis or occlusion of large cerebral arteries such as the intracranial internal carotids and middle cerebrals. Stroke typically occurs without warning and causes significant long-term neurologic sequelae in at least 50% of cases. Chronic transfusion after a first stroke reduces markedly the high risk of recurrent stroke, but this is a suboptimal approach because it does not prevent the initial neurologic injury.

The use of TCD and chronic transfusions to prevent first stroke is an exciting development. However, a number of important issues continue to limit the implementation of this approach:

1. Standardization of the TCD procedure may be problematic. The published data were generated by TCD studies performed by technicians trained at a single center who used a standardized protocol with identical equipment. Efforts by others to reproducibly measure blood velocity using more advanced and more widely available ultrasonography equipment have shown differences. Thus, unless the procedure is carefully standardized, measurement of blood velocity will not necessarily be comparable to published studies.

2. Chronic transfusions are costly and associated with significant morbidity and some mortality from transfusion-related infections, alloimmunization, and hemosiderosis. As many as 70% of TCD-positive patients may never have a stroke if not transfused. Thus, TCD screening may expose more patients to significant risk than the number that benefit. The duration of chronic transfusion needed for primary stroke prevention is unknown and the subject of an ongoing clinical trial.

Thus, our group feels that it is premature to recommend that all sickle cell anemia patients with sickle cell anemia be routinely screened with TCD. Screening requires that the method be reproducibly established at individual centers according to the protocol established for children with sickle cell disease (details available at http://www.neuro.mcg.edu/cvhp/stop). Once standardized, TCD screening can be offered to families, with disclosure of pros and cons and alternatives to chronic transfusions for children with positive results. This approach will facilitate informed decision-making by families. Chronic transfusions should be discussed with families of children at high risk for stroke, but data are currently insufficient to recommend that all such patients be transfused indefinitely. Finally, we recognize that information about this issue is rapidly evolving, and that approaches to TCD screening will vary among institutions.

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References