EWJ Dec 2023 - Journal - Page 53
Understanding MTBI: Incidence,
Classification, Evidence & Implications
by Dr Tracey Ryan-Morgan
Consultant Clinical Neuropsychologist, Talis Consulting Limited
• Loss of Consciousness
Similar measurement difficulties apply to assessing
length of loss of consciousness, particularly in cases
where the individual may have been under the influence of substances immediately prior to injury. In
my clinical experience, patients with MTBI often
grossly over-estimate the amount of time that they lose
consciousness for, if at all. The best sources of corroborative evidence are from witnesses at scene and the
contemporaneous ambulance records. It is possible to
sustain a mild traumatic brain injury without a loss of
consciousness.
How common is MTBI?
It is an established fact that “more than 90% of all
TBI cases are classified as mild, based on a GCS of 1315” (Maas et al, The Lancet, 2022 p.1033). It is important to understand how injuries to the head and
brain are categorized. The following indicators are
commonly referred to in order to classify whether a
head injury constitutes a TBI with the caveat that not
all head injuries result in a brain injury.
How do we classify brain injuries?
• Level of awareness / consciousness (Glasgow
Coma Scale Score: GCS)
GCS comprises three separate measures (Eye, Verbal,
Motor) all of which can be confounded by the presence of substances ingested prior to the injury or by
the administration of medications at scene or on arrival at the ED. Research indicates that GCS on arrival
at A&E is the more reliable prognostic indicator than
GCS at scene (Lesko et al, 2013). Allen et al (2013)
highlight clearly that a GCS of 8 can mean different
outcomes due to the heterogeneity of TBI injuries
(Extra Dural Haematoma vs Diffuse Axonal Injury vs
Sub Dural Haematoma vs Contusion, for example). For that reason, GCS is not considered to be a
particularly robust prognostic indicator.
EXPERT WITNESS JOURNAL
•Post Traumatic Amnesia (PTA)
PTA is notoriously difficult to assess retrospectively as
many patients who receive pre-hospital care can have
orthopaedic injuries for which they are administered
opiate analgesia. This confounds measurement of
PTA (McCarter et al, 2007). Ruff et al (2009) discuss
the difficulties of extrapolating genuine memories
from information the person has been told or has surmised. Unless formally measured using a recognised
measure such as the Westmead PTA scale, subjective
measurement tends to be unreliable. PTA is explored
in more detail below.
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DECEMBER 2023