Primary objective: To explore the heterogeneity of mild traumatic brain injury (mTBI).

Methods and procedures: Hospital-based prospective follow-up study of 125 patients with mTBI sub-divided into 'severity' sub-groups on the basis of GCS scores (GCS of 15 = mild sub-group; GCS of 13-14 = moderate sub-group). Post-traumatic amnesia (PTA) duration (30 minutes used as a cut-off) was also used to define group membership for secondary analyses. The follow-up assessment consisted of a brief neuropsychological battery as well as measures of neurobehavioural functioning, community integration and post-concussive symptomatology. CT scanning was also obtained when clinically relevant.

Main outcomes and results: The two mTBI sub-groups, as defined by GCS scores, did not differ with respect to post-concussive symptomatology, neurobehavioural symptoms, neuropsychological performance or CT scan abnormalities. In contrast, when group membership was redefined on the basis of PTA, the two sub-groups differed significantly with respect to intracranial abnormalities and report of aggressive or disinhibited behaviours at the 6-month mark.

Conclusions: While the notion of heterogeneity in mTBI was not supported when severity was based on GCS scores, there was partial support when PTA duration was used as a measure of severity.