How Strokes Develop
Originally, it was thought that strokes in SCD children were caused by the sickle-shaped red blood cells clumping up and blocking smaller blood vessels leading to the brain. However, research has shown that larger arteries going to the brain are the primary site of strokes in SCD patients. Because the sickled red blood cells are rigid, they tend to clump up along the walls of these larger arteries, damaging vessel walls and exposing tissue that gathers more sickle cells and further narrows the vessels.
Recurrent Strokes in Sickle Cell Disease Children
Children who have suffered a stroke in the past have a high risk of having another stroke. SCD children have a 67 percent risk of recurrence with strokes recurring up to nine months apart.
The cause of such a high rate of recurrence is believed to be a rise in white blood cell count accompanied by a drop in hemoglobin (the protein in red blood cells that carries oxygen) after the first stroke.
“Silent” Strokes in Sickle Cell Disease Children
Recurrent overt strokes are not the only problem for SCD children. So-called “silent” strokes can also cause significant morbidity. Strokes are usually diagnosed by observing motor deficits, but silent strokes occur without obvious outward symptoms like movement difficulties. They can be detected only through brain imaging devices such as MRIs. It’s estimated that 17 percent of SCD children under the age of 14 have silent strokes and the rate increases to 23 percent by the age of 18, with the size and number of lesions increasing.
Silent strokes often occur in frontal areas of the brain, the area responsible for executive abilities (mostly having to do with academic achievement and memory). These strokes can impair intellectual ability, academic ability, attention, visual-spatial skills, language, and long-term memory. Early detection through screening and brain imaging is of the utmost importance, since imaging can help prevent recurrences.
Predictors of stroke in Sickle Cell Disease children
By far, the strongest predictor of stroke in children with SCD is a previous stroke. In predicting the risk of stroke in SCD children without a previous event, studies have revealed signs or symptoms that often occur before a stroke. These may include:
- A history of seizures
- A previous transient ischemic attack (TIA) or “mini-stroke”
- New or increased frequency of pain syndromes such as acute chest syndrome (ACS)
- Nervous system infections
- Increased blood pressure
- Decreased hemoglobin level
- An abnormal result on an image of cerebral arteries called a transcranial doppler (TCD) ultrasonograph
- Increased white blood cell count
- Increased cerebral blood flow pressure
- A history of snoring and/or confirmation of sleep apnea (a condition in which breathing stops briefly during sleep)
If your sickle cell child has any of these conditions, please discuss them and the possibility of stroke with your physician.
Remember: For children with a high risk of stroke, or a history of stroke, blood transfusions can help prevent occurrence or recurrence.