Post Traumatic Amnesia


It never ceases to amaze me how poorly understood this crucial concept is when it is fundamental to diagnosing a cerebral injury. Not only by solicitors, who can be excused as non-medical people, but by some medical experts who must carry out this assessment properly to be able to confirm or deny its presence.

The reason that post traumatic amnesia (PTA) is so important in legal cases is because it is the gateway to proving that a cerrebral injury was sustained. PTA is widely accepted as the single most reliable indicator of both presence and severity of head injury.

Scans such as CT, MRI, SPET and SPECT often don’t identify any injury because the damage is too microscopic to be seen. Simple scales of assessment such as the Glasgow Coma scale used in hospitals are far too crude to be of any use and it should be noted that a maximum Glasgow Coma score of 15/15 does not rule out brain injury. A patient can have a maximum score of 15 yet still be in dense post traumatic amnesia.

Post traumatic amnesia is defined as the amount of time to restoration of clear and uninterrupted memory. It is characterised, not by unconsciousness, nor by a total lack of memory for the event, although some Neurologists mistakenly believe this to be the case.

It is characterised by “islands” or “snapshots” of memory interspersed with often longer periods where no memories are laid down at all. Consequently a person in post traumatic amnesia may appear and be referred to in the hospital notes as “alert and orientated” and will be perfectly capable of responding to simple questions. For this reason the average hospital A&E doctor will see a patient behaving normally and assume that nothing is wrong, when often the patient is in post traumatic amnesia.

Another reason why head injury is missed at hospital is because often the effects do not become apparent for up to 72 hours. This is because when the axons in the brain are stretched as a result of acceleration/deceleration forces, it takes some time (up to 72 hours) for a cascade of events to take place that leads to brain cell damage.

A study conducted by the American Army on the subject of undiagnosed head injury concluded that 52% of all head injuries are not diagnosed, so perhaps we should not be surprised that often there is no evidence of head injury in the contemporaneous records.

With post traumatic amnesia it is the patient’s lack of memory for key events, taken together with events that they do remember that helps to identify the post traumatic amnesia.

The islands or snapshots of memory associated with PTA have been demonstrated to last for many years rendering retrospective assessments of PTA entirely valid. It is possible to corroborate a patient’s account of PTA by taking evidence from a witness who was also present at the scene who will probably hold memories for the “key” events that the Claimant has lost.

The difficulty for Claimant solicitors is that Defendants experts rarely perform thorough PTA assessments, if at all. If one is performed it is likely to be rushed and incomplete. Some Neurologists instructed by the defence spend far less than an hour with the Claimant in total which will prevent them from performing a sufficiently detailed assessment of PTA.  An assessment of PTA is a time consuming process to perform properly because the consultant will need to go through the events frame by frame, if absence of memory for key events is not to be missed. It is important to assess the duration of PTA accurately because it’s length determines the severity of the initial cerebral insult. PTA of at least 30 minutes but under one hour represents a mild head injury, over one hour but less than 24 hours represents a moderate head injury, over 24 hours but less than one week represents a severe head injury, over one week but less than one month represents a very severe head injury and PTA over one month represent an extremely severe head injury.

There is actually a pretty poor correlation between initial injury severity and outcome (0.3). This means that someone may make a good recovery from a severe head injury but someone who has only sustained a mild head injury may be badly affected. There is no hard and fast rule, although previous head injuries will render a person more vulnerable to subsequent cerebral injury.

By performing a quick and substandard assessment for PTA the bad clinician will often miss its presence which will enable him or her to conclude that a head injury has not been sustained and avoid investigating the head injury further. Often where a head injury has been sustained the Claimant will present with a fairly typical pattern of cognitive and behavioural deficits as well as head aches and persistent fatigue.

All of these symptoms must be investigated and teased out by the clinician but if his history taking fails to find any evidence of PTA he will usually stop there, fail to investigate further and conclude that no head injury has been sustained. In my experience of specialising in subtle brain injury cases it is rare for a head injury expert instructed by the Defence to identify any clinically significant PTA. They usually deny its presence because that enables them to say that a head injury has not been sustained.