Retrospective assessment of post traumatic amnesia (PTA) following a traumatic brain injury is sometimes necessary when it wasn’t measured prospectively at the time of injury—something that can happen for a variety of reasons. For example, a patient might arrive at the hospital already out of PTA, or they may have been treated at a facility that doesn’t routinely administer a prospective PTA measure, such as the Westmead PTA Scale or similar assessments. This is especially common in smaller hospitals, country centres, or emergency situations where documentation can be limited. Alternatively, the neuropsychologist may be working with someone years after their injury, with no available records or detailed contemporary assessment.
Why Retrospective Assessment is Used #
- Lack of real-time data: If the PTA wasn’t measured prospectively, clinicians must estimate duration retrospectively, often for diagnosis, severity classification, or medico-legal purposes.
- Historical cases: Many older cases pre-dated the routine use of prospective PTA measurement, so retrospective methods are the only way to estimate severity.
- Late presentations/referrals: Individuals might present for assessment well after the injury, especially for legal or compensation claims, making retrospective estimation necessary.
Assessment Challenges #
Challenges with Retrospective Assessment #
- Reliability of patient memory: By definition, PTA is a period during which a patient cannot form new memories. Asking someone to recall when their memory returned to normal can be inherently unreliable, as they may have “islands of memory” or patchy recollections.
- Dependence on secondary sources: Clinicians may need to rely on ambulance records, witness statements, ED notes, and family/carer reports. Sometimes these are incomplete or inconsistent.
- Confounding factors: Factors like medications (e.g., anaesthesia or opioids), psychological shock, pain, or intoxication at the time of injury can affect both memory and documentation.
- Subjectivity: The process involves reconstructing a timeline by asking about last clear pre-injury memory and first clear post-injury memory, and then verifying details through available documentation. This is less precise than systematically testing memory and orientation in real-time.
- Short duration in mild TBI: For many cases of mild TBI, the period of PTA can be just minutes to a few hours—by the time the patient presents for care, they may already be oriented, making it difficult to determine duration accurately.
Challenges with Prospective Methods (for comparison) #
- Resource-intensive: Prospective PTA requires repeated, structured assessment (e.g., the Westmead PTA Scale), which can be challenging in busy EDs or for patients who are quickly discharged.
- Missed window: If not initiated soon after injury, the prospective measure won’t capture the full duration of PTA.
Summary #
Retrospective assessment is often a pragmatic necessity but comes with significant limitations regarding accuracy and reliability. Prospective methods are preferred whenever possible, as they yield more objective, standardised data, but are not always feasible in real-world settings. Good clinical practice involves triangulating information from multiple sources and using the best available evidence from records and interviews to form an estimate, keeping in mind its potential for error.
