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

J Neurol Neurosurg Psychiatry. 2012 Nov;83(11):1048-55

Königs M, de Kieviet JF, Oosterlaan J

CONTEXT: 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.
OBJECTIVES: 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.
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.
RESULTS: 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 (Q(1) =3.85; p<0.05)
but not in the chronic phase (Q(1) =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).
CONCLUSIONS: PTA duration is a valuable predictor of intelligence impairment
following TBI. Results support the routine assessment of PTA duration in clinical
settings.

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