Silent strokes, which have no immediate symptoms but could cause long-term cognitive and learning deficits, occur in a significant number of severely anaemic children, especially those with sickle cell disease, according to research.
One-quarter to one-third of children with sickle cell disease have evidence of silent strokes in their brains, according to Michael M. Dowling, M.D., Ph.D., lead author of the study and assistant professor of paediatrics and neurology at the University of Texas Southwestern Medical Centre in Dallas.
"These are five- to 10-year-old children who have brains that look like the brains of 80-year-olds," Dowling said. "These strokes are called 'silent' because they don't cause you to be weak on one side or have any obvious neurologic symptoms. But they can lead to poor academic performance and severe cognitive impairments."
Sickle cell disease
Sickle cell disease is a blood disorder characterised by low levels of haemoglobin, the iron-containing component of red blood cells that carries oxygen.
Low haemoglobin causes anaemia. In sickle cell disease, the blood cells are misshapen (sickle-shaped) and may form clots or block blood vessels. About 10% of children with sickle cell disease suffer a stroke. Blood transfusions can reduce the high risk of repeat strokes.
Dowling and colleagues hypothesised that silent strokes occur during severe anaemia and may be detectable by MRI. They used MRI on the brains of 52 hospitalised children, two- to 19-years-old at Children's Medical Centre Dallas with haemoglobin concentrations dropping below 5.5 g/dL.
They compared severely anaemic children with sickle cell disease to a group of children without sickle cell disease who had haemoglobin levels below 5.5 g/dL.
They identified silent strokes in about 20% of the children with sickle cell disease who were experiencing acute anaemia. They also saw evidence of silent strokes, though not as often, in severely anaemic children who didn't have sickle cell disease.
The many reasons, besides sickle cell disease, why children could have anaemia include trauma, surgery, iron deficiency or cancer such as leukaemia.
"These are brain injuries that go unnoticed by doctors, unless the children have testing with a special MRI," he said. "We looked at every child who went to the hospital for a 30-month period and identified about 400 children who came in with haemoglobin below 5.5 g/dL. That represented about 12% of the admissions for sickle cell disease and about 1% of the total admissions to Children's Medical Centre."
The findings suggest that children with or without sickle cell disease who have acute anaemia could be suffering undetected brain damage. The researchers suggest that all children with severe anaemia need careful examination for silent strokes.
Improved recognition and timely transfusion to increase blood haemoglobin levels could prevent permanent brain damage in children with silent strokes, according to the study.
Future studies should look at larger groups of children for longer periods to better understand the impact of acute anaemia on children, Dowling said. (EurekAlert/ February 2011)