Stroke risk increases over a hundredfold in children living with sickle cell disease compared to children who do not have sickle cell disease. Sickle cell is a serious inherited blood disorder where red blood cells, which carry oxygen around the body, develop abnormally. Normal red blood cells are flexible and disc-shaped, but in sickle cell disease, they can become rigid and crescent-shaped. Sickle cells are not only less flexible than healthy red blood cells, but also stickier. This can lead to the blockage of blood cells, resulting in tissue and organ damage and episodes of severe and excruciating pain. The sickle-shaped blood cells are also more fragile and break apart, which leads to fewer red blood cells in one’s body; this is known as anaemia. Sickled red blood cells can block blood flow in vessels in the brain, leading to a ‘silent’ stroke.
The compromised hemoglobin that is characteristic of sickle cell disease presents a serious danger to the brain. Minutes without oxygen can kill brain cells. The tissue called grey matter in the brain and spinal cord are made of cell bodies. The white matter is composed of nerve fibres. Grey matter is composed of neurons, the brain cells that store information. White matter is the network of highways in the brain that neurons use to transmit this information. Studies demonstrate that the body differentiates between grey and white matter, clearly prioritising neurons. This makes sense because keeping neurons alive is critical for survival.
Strokes in the grey matter are immediately catastrophic, while strokes in white matter appear silent because they simply cause informational processing to slow. Though they may not cause major motor defects, the effects of white matter on ‘silent’ strokes can greatly impede important aspects of a patient’s day-to-day life. For example, ‘silent’ strokes can have debilitating effects on executive function, the brain’s ability to execute complex tasks needed for things like maintaining a job, thinking, learning, decision-making, or doing well in school. ‘Silent’ strokes are equally a factor for future strokes.
Similarly, under the stress of low oxygen in SCD, blood flow is diverted to neurons in the grey matter to prevent their death. A study found that oxygen delivery to the white matter was critically sensitive to the hemoglobin level. The more severe the anaemia, the lower the oxygen delivery to the white matter in the brain.
Due to a genetic mutation affecting the hemoglobin, the component of the red blood cells that carries oxygen reduces the amount of oxygen supplied to vital tissues and organs. Blood cells are deformed in a characteristic crescent shape and lodged into the smallest blood vessels, blocking blood flow, and leading to intense pain. On top of these symptoms, patients face a high risk of stroke, and this is the leading cause of death in sickle cell disease. ‘Silent’ strokes are common, occurring in 39% of people living with SCD by 18 years of age.
There are two tests that can be used to identify children at higher risk of having a first stroke. Transcranial doppler ultrasonography (TCD) measures the speed of blood flowing through the arteries in the brain; this test is painless. Children with high blood flow have an increased risk of stroke. Magnetic resonance imaging (MRI) takes images of the brain to see if there are small areas of damage called ‘silent’ strokes. Children with ‘silent’ strokes have an increased risk of clinical stroke.
There are two types of strokes that people living with sickle cell experience. Ischemic stroke: this happens when blood flow to the brain is blocked. This stroke is typically diagnosed in people living with sickle cell, especially children showing symptoms of a brain complication when a test or an MRI is done. Haemorrhagic stroke: this happens when blood vessels burst and bleed in the brain. This stroke is most common among young people between the ages of 20 to 29 and adults. However, both types of strokes can occur at any age.
Treatments that have been considered over the years for preventing ‘silent’ strokes include long-term red blood transfusions, the tablet called hydroxyurea and stem cell transplant, also known as bone marrow transplant.
References: www.cochrane.org; www.sciencedaily.com ; www.stroke.org; www.sciencedaily.com
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source: healthwise.punchng.com
