About post-traumatic amnesia

What post-traumatic amnesia is, how it relates to injury severity and indications for testing.

People who sustain a traumatic brain injury (TBI) may experience a temporary clinical state known as post-traumatic amnesia (PTA).

PTA represents a stage of recovery during which impairments affect a person’s orientation, day-to-day memory and behaviour. PTA can last for a few minutes to many weeks or months.

Why we test for PTA

PTA has implications for patient care, rehabilitation, clinical assessment, and interactions with family and carers.

Identifying when a person is experiencing PTA helps to:

• optimise post-concussion and head injury assessment and management
• guide readiness and suitability for certain assessments (e.g. neuropsychological testing), interventions and rehabilitation
• determine injury severity and the prognosis for recovery
• protect vulnerable people in areas such as medical consent, financial management, reputation/relationships and other legal matters
• ensure patient safety, e.g. people with PTA are at greater risk of behavioural disturbance and/or absconding, and therefore may require increased supervision and cognitive monitoring
• inform research.

PTA duration, injury severity and prognosis

The duration of PTA correlates with TBI severity, i.e. longer durations of PTA are associated with more severe cognitive impairment. This increases the likelihood of long-term impacts on daily life and cognitive recovery (Ponsford et al. 2023).

Use a range of clinical markers when assessing TBI severity and estimating prognosis, including:

• duration of PTA
• duration of unconsciousness
• neuroimaging findings
• mechanism of injury
• Glasgow Coma Scale (GCS) scores
• general clinical progress
• presence of confounding conditions or factors.

The following table offers a general guide for classifying TBI severity (Khan et al. 2003). It is based on the duration of PTA measured using the Westmead PTA Scale for moderate and severe TBI and the Abbreviated Westmead PTA Scale (A-WPTAS) for mild TBI. The severity threshold values are cut-offs based on established clinical practice in Australasia. While more recent research has suggested alternative values, no clear consensus has been established (Vile et al. 2022).

In some jurisdictions, eligibility for services and insurance schemes is based on PTA duration and injury severity. Clinical expertise is often required when classifying TBI severity, as there are multiple factors that influence long-term outcomes.

More about the Westmead PTA Scale and A-WPTAS

Clinical indications for PTA testing

People in PTA may experience a range of symptoms that can affect physical, cognitive and behavioural functioning. Not all signs and symptoms need to be present – even a single attribute can indicate the possibility of PTA.

Start PTA testing when any of the following are present in people with acute head trauma and/or suspected TBI:

• Loss or altered level of consciousness, as indicated by a Glasgow Coma Scale score of less than 15 (consult ambulance records as well as accident and emergency notes).
• Reported loss of consciousness at the scene, e.g. by a witness or from the patient.
• Evidence of brain injury on a cerebral CT scan or MRI.
• The patient seems vague or disorientated, or is having difficulty remembering things that they are told.
• Nausea, vomiting, headache, dizziness, sensitivity to lights and sounds, visual changes or fatigue (symptoms of concussion).
• Indications of head involvement (e.g. fracture, bruising, laceration) and where there are gaps in the patient’s memory.
• Alcohol or drug intoxication causing clouding of consciousness when brain injury cannot be excluded.

Interpret results from PTA testing cautiously and appropriately.

Consider alternative diagnoses that can influence testing performance, such as:

• prior brain injury or other pre-existing conditions that may impact cognitive function, e.g. learning difficulties, intellectual disability or dementia
• pharmaceutical side effects, e.g. anaesthesia, sedation and analgesia
• drug, alcohol or other substance intoxication
• concurrent acute clinical issues, e.g. simultaneous acquired brain injury, surgical intervention, delirium, psychiatric illness.

References