PARENTS who assault their children usually claim the injuries happened by accident. Sometimes doctors can't say for sure what really happened. But researchers in Pittsburgh may now be on the way to identifying a biochemical signature that can help distinguish between brain injuries caused by accidents and those resulting from violent abuse.
The team, led by Patrick Kochanek of the University of Pittsburgh School of Medicine, is analysing cerebrospinal fluid from children and adults. The researchers are comparing fluid drained from patients with severe head trauma to relieve a build-up of pressure with fluid from patients given spinal taps for other reasons.
Some of the children studied had been injured by adults who admitted abusing them. Preliminary evidence suggests that victims of abuse usually have a "whole host of biochemical derangements in the brain", says Kochanek. His team has studied a range of biochemicals, including amino acids, immune system signalling molecules called cytokines, and quinolinic acid, produced by immune cells that slowly infiltrate the brain after an injury.
"With any metabolite that we look at, seven times out of 10 we see really high levels in victims of child abuse," says Kochanek. "I think it really is a reflection of how severely these infants are injured."
High levels of quinolinic acid may be the closest thing so far to a "marker" of child abuse, says Kochanek. Adults who assault children usually don't take them straight to hospital-instead, they show up later with a story about how the child was injured in a fall, or some other "accident". Because quinolinic acid accumulates slowly in the brain, its presence may reveal whether a parent is lying about the timing of the injury. High levels might also indicate prior injuries, signalling a history of abuse.
Kochanek and his colleagues could find no trace of quinolinic acid in cerebrospinal fluid taken from 39 adults with head injuries who went to hospital within 24 hours of being injured. But in a study to be published early next year in the Journal of Critical Care Medicine, conducted with Melvyn Heyes of the National Institute of Mental Health near Washington DC, they say that two out of 17 children with head injuries had high levels of quinolinic acid. Both children had been abused. A third abused child in the sample did not have elevated levels of quinolinic acid. Kochanek is now expanding the study. "We need to study more patients to determine if this preliminary finding holds up or not," he says.
The team has also found that the cerebrospinal fluid of babies who have been shaken violently contains particularly high levels of the amino acid glutamate-which causes further damage to neurons in injured brains. Randall Alexander, former vice-chair of the US Advisory Board on Child Abuse and Neglect and a paediatrician at the Morehouse School of Medicine in Atlanta, says that this is further evidence that victims of shaken baby syndrome can suffer more widespread damage than those who receive blows to the head.
Kochanek warns that levels of a single biochemical are unlikely ever to give a definitive diagnosis of whether or not a child has been abused. But analysed together with other evidence, such as X-rays, he believes biochemistry could become an important tool for doctors investigating suspicions of abuse.
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