Download Mild TBI causes a long-lasting elevation of the

Mild TBI causes a long-lasting
elevation of the transcranial
magnetic stimulation (TMS) motor
threshold
Jussi Tallus 1, Pantelis Lioumis2, Heikki Hämäläinen3,
Seppo Kähkönen2, Olli Tenovuo*1
1Department of Neurology, University of Turku,
Finland, 2Biomag Laboratory, Finland, 3Department of
Psychology, University of Turku, Finland
* presenting author
Introduction
• Mild traumatic brain injury (mTBI) is often
associated with long lasting symptoms that
may be caused partly by diffuse damage to
cerebral white matter tracts
• There is a major clinical need to develop
reliable methodology to assess whether
prolonged symptoms after mTBI have an
organic basis
Introduction
• Cortical excitability can be evaluated by
recording electromyographic (EMG)
responses elicited by single pulse TMS and
measuring the minimum intensity (motor
threshold; MT) that can evoke motor evoked
potentials (MEPs).
• MT provides a relatively easy measure of
corticospinal tract integrity.
Objectives
To evaluate whether corticospinal tract
integrity measured with TMS elicited MT
measurement is altered in subjects with
chronic symptoms after mTBI
Material and methods
• Nineteen mTBI patients, 11 with persistent
symptoms and 8 recovered
• The subjects had suffered a mTBI (GCS 13 – 15)
on the average five years earlier
• All subjects had normal MRIs in visual inspection
• Nobody used CNS affecting medications
• Nine healthy controls
Material and methods
• Navigated TMS, stimulation on the left primary
motor cortex
• MEPs recorded from the right m. abductor
pollicis brevis by EMG
• MT is defined as the lowest stimulation intensity
at which 5 out of 10 pulses evoke 50 µV MEP or
greater
Results
• The average MT was 43.0 % (SD ± 0.8) of
maximum stimulator output in the control
group.
• Both patient groups had statistically significantly
higher MTs, 52.5 % (SD ± 3.1) in the symptomatic
and 54.6 % (SD ± 3.4) in the recovered group.
Results
p = 0.012
p = 0.011
Conclusions
• MT may be a useful measure in evaluating brain
damage caused by mTBI.
• This study shows that MT elevation can last until
at least several years after the injury, and that it
is not necessarily related to subjective
complaints.
Conclusions
• The similar results of the symptomatic and
recovered groups imply that simple MT by itself
is not sufficient as a measure of injury severity
or outcome, but it can be useful in combination
with other methods.
• It is noteworthy that also fully recovered mTBI
subjects show an abnormal MT, which suggests a
persistent injury also in these subjects