Post-traumatic amnesia predicts intelligence impairment following traumatic brain injury: a meta-analysis

Worldwide, millions of patients with traumatic brain injury (TBI) suffer from persistent and disabling intelligence impairment. Post-traumatic amnesia (PTA) duration is a promising predictor of intelligence following TBI.

To determine (1) the impact of TBI on intelligence throughout the lifespan and (2) the predictive value of PTA duration for intelligence impairment, using meta-analytic methods.

Electronic databases were searched for peer reviewed articles, published until February 2012. Studies reporting intelligence following TBI and injury severity by PTA duration were included. Meta-analytic methods generated effect sizes for full scale IQ (FSIQ), performance IQ (PIQ) and verbal IQ (VIQ), following mild TBI (PTA duration 1-24 h) and severe TBI (PTA duration >7 days), during the subacute phase of recovery (≤6 months post-injury) and the chronic phase (>6 months post-injury). Meta-regression elucidated the predictive value of PTA duration for intelligence impairment.

Patients with severe TBI exhibited large depressions in FSIQ in the subacute phase of recovery (d = -1.07, 95% CI to 1.52 to -0.62; p<0.001), persisting into the chronic phase (d = -0.78, 95% CI -1.06 to -0.51; p<0.001). PIQ was more severely affected than VIQ in the subacute phase (Q1 =3.85; p<0.05) but not in the chronic phase (Q1 =0.03, p=0.87). Most importantly, longer PTA duration strongly predicted greater depressions of FSIQ and PIQ in the subacute phase (-0.76 ≤ βs ≤ -0.73, Ps<0.01) and FSIQ, PIQ and VIQ in the chronic phase (-0.80 ≤ βs ≤ -0.61, Ps<0.05).

PTA duration is a valuable predictor of intelligence impairment following TBI. Results support the routine assessment of PTA duration in clinical settings.