Post-traumatic amnesia

Abstract

Of patients hospitalised for traumatic brain injury (TBI), most pass through a state of altered consciousness known as “post-traumatic amnesia” (PTA). Despite the lack of a consistent definition, PTA is widely used as a construct in neurosurgical practice to guide decision-making and prognosis. Accurate PTA assessment is important, because over-evaluation leads to excess social, financial and opportunity costs, whilst under-evaluation risks patient welfare. Whilst anterograde memory is certainly disrupted in PTA, PTA in fact involves a far more extensive memory disturbance. More instructively, the complete “post-TBI syndrome” also comprises an extensive cognitive deficit which includes a confusional state, as well as a behavioural disturbance characterised by acute agitation. Recently, impairments in attention and executive functioning have also been emphasised; indeed, some consider these the primary disturbance with PTA. Although all of these features were fully described (or implied) by the earliest pioneers, most current PTA scores do not assess the complete “post-TBI syndrome”. Currently, the Westmead PTA scale (WPTAS) directs most in-hospital TBI management throughout Australasia: however, in addition to general defects, specific limitations have been identified in the levels of evidence for WPTAS validity. We review the literature regarding PTA and, in particular, the continued role of the WPTAS in directing neurosurgical practice.

Introduction

Traumatic brain injury (TBI) is a significant worldwide health issue, with an incidence of between 107–149 per 100,000 throughout Australia.1, 2 Peak TBI incidence occurs predominantly in males between 16–24 years old, and mostly results from motor vehicle accidents, assaults, falls, and sporting accidents. Alcohol is frequently involved.³ Whilst the majority (80%) of TBI are mild, moderate-to-severe injuries form the focus of neurosurgical care.

Recovery from TBI can be described in three progressive phases: (1) loss of consciousness (coma), (2) altered consciousness (designated “post-traumatic amnesia” [PTA]), and (3) rehabilitation with normal consciousness (where physical, cognitive and behavioural functioning potentially return to premorbid levels, notwithstanding any permanent deficits).⁴ In hospitals, numerous psychometric scoring systems have been developed to asses PTA (Table 1), however in the sporting arena, where the terms “concussion and post-concussive syndrome” are often preferred, separate scoring systems have been developed instead.⁵ PTA duration appears to correlate with TBI severity6, 7, and of patients hospitalised for TBI at least 70% experience PTA through to the rehabilitation referral stages.8, 9

Despite the lack of a consistent definition, PTA duration is nevertheless widely used as a construct in neurosurgical practice to guide decision-making and prognostic assessment. PTA is used as a tool for determining (1) decision-making competence for patients, (2) the degree of patient supervision necessary, (3) referral for rehabilitation, (4) timing of leave, and (5) discharge planning.10, 11, 12, 13 PTA duration is also used to prognosticate (1) cognitive abilities following TBI, (2) length of hospital stay, (3) risk of early and late epilepsy, and (4) likely functional outcome on discharge.14, 15, 16

Given the above, an accurate assessment of PTA and its duration is important. Over-estimation can lead to excess social, financial and opportunity costs, especially in regional hospitals which service wide geographical regions. Social costs include in-patient stays in an unfamiliar location away from family and friends. Economic costs include both public and personal expenses, such as family relocation, sometimes for prolonged periods of time. Opportunity costs derive from the prevention of treatment of others through unnecessary bed occupancy. Given the central place of PTA in TBI management, accurate definition, measurement and criteria for PTA emergence should be paramount. The scoring system adopted must have a firm evidence-base, broad application across disciplines, and be simple to use.