Cognitive outcome following complicated mild Traumatic Brain Injury: A literature review and meta-analysis.

Cognitive outcome for mild TBI with positive brain imaging (complicated MTBI) was compared with that for mild TBI with normal imaging (uncomplicated MTBI) and moderate to severe TBI using meta-analysis. Twenty-three studies utilising objective neurocognitive tests were included in the analysis. At less than 3 months post-injury, complicated MTBI was associated with poorer cognitive outcomes than uncomplicated MTBI but deficits were not comparable to those with moderate-severe TBI. After 3 months post-injury a similar pattern was detected. Beyond 3 months, relative deficits in complicated MTBI to those with uncomplicated MTBI were present in processing speed, memory, executive function and language, though the latter may be due to reduced semantic fluency. The effect size of deficits in these domains was more marked in moderate-severe TBI. The available data supports the use of complicated MTBI as a distinct classification in the prediction of cognitive outcome. The size of cognitive deficit in complicated MTBI was small and unlikely to cause significant disability. However, complicated MTBI is a broad category encompassing individuals who may differ markedly in the nature and extent of intracranial imaging abnormality and further studies are warranted. Limitations of the available studies include small, selected samples, variations in TBI severity classification, absence of validity ('effort') testing, differing imaging methodology and lack of long-term follow up.