Research Letter: Retrograde Amnesia and Posttraumatic Amnesia in Service Members and Veterans With Remote History of TBI.

Objective: The recently updated American Congress of Rehabilitation Medicine diagnostic criteria for mild traumatic brain injury (mTBI) removed retrograde amnesia (RA) as a main criterion for mTBI, recommending it be included as a substitute criterion only when posttraumatic amnesia (PTA) cannot be reliably assessed. This study aimed to investigate the evidence base for this recommendation.

Setting: Military treatment facility.

Participants: A total of 752 US military service members/veterans (mean age = 36.1 years, SD = 9.4 years) with a history of TBI prospectively enrolled in the Defense and Veterans Brain Injury Center-Traumatic Brain Injury Center of Excellence 15-Year Longitudinal TBI study who sustained a total of 1015 TBIs with substantiated RA and PTA. Most participants were male (93.6%), not of Hispanic Origin (84.7%), and White (84.5%). Evaluations were conducted on average 7.6 years (SD = 6.9 years) after injury.

Design: Case series.

Main Measures: Presence and duration of RA and PTA; and ratio of PTA and RA (PTA:RA).

Results: There were no TBIs where RA was present but PTA was absent. Within the 1015 TBIs, 896 (88.3%) involved both RA and PTA, 65 (6.4%) involved PTA only, and 54 (5.3%) did not involve RA or PTA. For the 635 TBI events with substantiated recorded minutes of RA and PTA both >0, the mean ratio of PTA:RA was 31:1. In only one instance was the ratio of PTA:RA <1.

Conclusion: There were no TBIs where RA was present without PTA. RA tended to be much shorter than PTA. Findings support the American Congress of Rehabilitation Medicine's decision to remove RA as a main criterion for mTBI.