Sickle cell disease is an inherited disease that is characterized by the presence of an abnormal hemoglobin. Stroke (most commonly ischemic) is a major complication of sickle cell disease, which typically develops when a person is between the ages of 9 and 15 years (20% risk by 20 years of age) but can be observed in adults as well (25% by 45 years of age). Cerebral infarction in sickle cell disease is associated with an occlusive vasculopathy that involves the distal intracranial segments of the cerebral arteries (usually stenosis or occlusion of the intracranial arteries of the circle of Willis, sometimes with a moyamoya disease appearance on arteriography), with documented thrombosis formation in some cases. As recommended by the National Heart, Lung, and Blood Institute and the American Stroke Association, transcranial Doppler ultrasound should be used more widely in children with sickle cell disease to detect elevated blood flow velocity (especially a velocity of 200 cm/s or more) indicative of vessel disease and high risk of future stroke. To decrease the risk of stroke in sickle cell disease, patients should be advised to avoid excesses of unaccustomed physical exertion, hypoxia (as occurs in high altitude or with climbing), exposure to excessive heat, stress, and acute infection. A primary prevention strategy for clinical stroke using chronic blood transfusions to keep the sickle hemoglobin (Hb S) below 30% of total hemoglobin was documented recently (90% risk reduction of stroke) in the Stroke Prevention in Sickle Cell Anemia trial. Other “anti-sickling” treatment strategies (such as hydroxyurea, “antiendothelial” therapy, and prevention of red cell dehydration) and agents such as decitabine and short-chain fatty acids are currently under investigation.

Management of other hematologic diseases (such as polycythemia, thrombotic thrombocytopenic purpura, dysproteinemia, thrombocythemia, and leukemia) and conditions and circumstances that result in a hypercoagulable state (such as cancer, pregnancy, trauma, postoperative period, postpartum period, and disseminated intravascular coagulation), which increases the risk of stroke, are specific to each underlying cause. (A more complete discussion of hematologic disease can be found in Chapters 16 and 17.)