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J Neurol (1991) 238 : 443-446
Journal
of
Neurology
© Springer-Verlag 1991
Tolerance for light and sound of patients
with persistent post-concussional symptoms
6 months after mild head injury
N. Bohnen 1, A. Twijnstra 2, G. Wijnen 1 , and J. Jolles 1
1Department of Neuropsychology and Psychobiology, University of Limburg, P.O. Box 616, NL-6200 MD Maastricht, The Netherlands
2Department of Neurology, University Hospital, Maastricht, The Netherlands
Received November 20, 1990 / Received in revised form April 4, 1991 / Accepted April 9, 1991
Summary.
Patients with post-concussional symptoms
(PCS) about 6 months after a mild head injury (MHI)
were examined for tolerance of light and sound in com-
parison with concussed patients without PCS and non-
concussed healthy controls. MHI patients with PCS were
individually matched with subjects from the two control
groups for the time elapsed from the injury, and for age
and sex. Using a computerized rating technique, we as-
sessed both the maximal and submaximal levels of low-
ered tolerance for light and sound over a wide range of
stimuli. We found that the MHI patients with PCS 6
months after the trauma (n = 11) tolerated significantly
less well stimuli of intensities of 71dB and 5001x than
MHI patients without PCS (n = 11) and non-concussed
controls (n = 11). There were no significant differences
in tolerance for light and sound between MHI patients
without PCS and the non-injured controls. Decreased
tolerance for light and sound may contribute to the per-
sistence of symptoms up to 6 months after a mild head
injury. The psychophysical method provides an objective
measure for the evaluation of the late persistent post-
concussional syndrome.
Key words:
Light - Sound - Tolerance - Post-concus-
sional syndrome
Introduction
Post-concussional symptoms (PCS) occur in many pa-
tients with mild head injury (MHI) [10, 11], and include
headache, dizziness, easy fatigability, insomnia, lowered
tolerance for noise and light, irritability and difficulty
with memory and concentration. Although patients may
recover completely within some weeks, there is a fairly
high proportion of patients who report symptoms after
the first weeks of recovery [13]. Because there is often
litigation when personal injuries are involved, especially
when the complaints persist, the validity of patient's per-
Offprint requests to: N. Bohnen
sistent PCS comes under question. Both organic and
psychological factors have been considered to explain
the occurrence of persistent PCS [10]. Neuropsychologi-
cal investigations to assess cognitive deficits after MHI
have indicated that subtle impairments in the rate of in-
formation processing and in reaction time are initially
present but may disappear within a couple of months [1,
9, 10]. Although repeated neuropsychological testing
has, up to now, not allowed a straightforward interpreta-
tion of whether or nor significant cognitive disability is
present, evidence indicates that a fairly high proportion
of MHI patients (over 20-50%) still complain of behav-
ioural dysfunction up to 3-6 months after injury [1, 9,
12]. The fact that a clear-cut organic or neuropsycholog-
ical dysfunction cannot be found leads to a more psycho-
genic interpretation of the persistent subjective symp-
toms [5, 12].
The objective testing of tolerance for light and sound
has been proposed as a procedure to obtain evidence of
an underlying organic dysfunction. Waddell and Gronwall
[16] demonstrated that MHI patients had a significantly
lower threshold tolerance for light and a slightly decreased
tolerance for sound 1-3 weeks after injury than healthy
controls. In addition, Jonsson et al. [8] found that MHI
patients with persistent symptoms on average 3 months
after the trauma had a decreased tolerance for light and
sound in comparison with both neurotic patients and
normal control subjects.
Unfortunately, there have been no psychophysical
studies that have objectively assessed the tolerance for
light and sound of MHI patients at later post-injury times
or compared MHI patients with and without PCS. The
aim of the present study was therefore, to compare the
maximal and submaximal levels of reduced tolerance for
light and sound stimuli of MHI patients with PCS with
those of matched patients without PCS and healthy non-
concussed controls. We also investigated whether pa-
tients without PCS had a different tolerance for light and
sound from non-concussed controls.
We used an objective method of assessing tolerance
for light and sound that not only measures the maximal
level of lowered tolerance, but that can also be used to
444
compare the submaximal levels of lowered tolerance by
applying a graded tolerance scale for each stimulus. Re-
cently, we found that MHI patients 3-6 days after injury
tolerated intense light and sound stimuli both at maximal
and at submaximal levels of reduced tolerance less well
than controls.
Non-uniform criteria for defining MHI have undoub-
tedly contributed to conflicting findings obtained in stud-
ies on the post-concussional syndrome. Clearly defined
eligibility criteria were applied in the present study, i.e.
patients with an uncomplicated MHI, a post-traumatic
amnesia of less than 60 min, a loss of conciousness of less
than 15 min and a Glasglow Coma Score of 15 on admis-
sion and the absence of a focal neurological deficit.
Subjects and methods
Patients were selected for post-concussional behavioural dysfunc-
tion from a larger group of patients who had participated in a com-
prehensive study of MHI patients. The criteria for inclusion in the
study included an elapsed time after the injury of about 6 months,
a period of unconsciousness ranging from some several seconds to
15 min, post-traumatic amnesia for less than 60 min, and an EMV
(Glasgow Coma) score on admission of 15. None of the patients
had evidence of a focal neurological deficit, or of a skull fracture.
Patients were excluded if they had consumed alcohol at the time of
the accident or if they had a history of pre-existing emotional prob-
lems. In addition, patients with hearing and visual problems were
not eligible. Eleven patients with persistent PCS were selected and
individually matched with both a patient without PCS and a non-
concussed control subject for sex, age (SD 5 years) and time
elapsed after injury (SD i-2 months). Normally, younger males
are over-represented in a head-injured population. The applica-
tion of strict eligibility criteria, especially the exclusion of intoxi-
cated subjects, may have reduced the male-to-female sex ratio in
the present study of patients with an uncomplicated MHI. The
non-concussed control subjects were recruited from a pool of heal-
thy volunteers. Data on sex, age and post-injury time for each
group are presented in Table 1. The study was approved by the
ethical council of the University Hospital and all subjects gave
their informed consent.
Table 1. Sex, age (years) and time (months) elapsed after injury.
Group I, MHI patients with persistent post-concussional symp-
toms: group It, MHI patients without symptoms; group III, non-
concussed healthy subjects
Group I Group II Group Ill
No. Sex Age Time No. Sex Age Time No. Sex Age
1 F
24 6.0
l F 22 5.0 1 F
22
2 M 34 6.5 2 M 36 6.5 2 M 29
3 M 24 6.0 3 M 24 7.0 3 M 26
4 F 23 6.0 4 F 25 5.0 4 F 22
5 F 47 6.5 5 F 42 8.5 5 F 47
6 F 18 6.0 6 F 18 6.0 6 F 18
7 M 44 6.0 7 M 39 6.0 7 M 43
8 M 27 5.0 8 M 22 6.0 8 M 30
9 F 20 7.0 9 F 16 5.5 9 F 19
10 M 35 6.5 10 M 36 6.0 10 M 38
I1 F 51 7.0 11 F 49 6.5 11 F 54
Mean 31.5 6.2 29.9 6.2 31.6
(SD) 11.4 0.6 10.9 1.0 12.1
Post-concussional symptoms
A checklist of PCS was completed, which included items such as
headache, dizziness and irritability. As these symptoms may also
occur in healthy individuals [5], the symptoms were scored for the
absolute or relatively increased appearance after the injury in com-
parison with the pre-traumatic condition. All patients with PCS
complained of three or more symptoms. The frequency of the re-
ported symptoms in the symptomatic patient group (n = 1 l) was as
follows: headache (n = 7), nausea (n = 1), fatigue (11 = 9), dizzi-
ness (n- 6), forgetfullness (n= 7), problems with concentration
(n = 8), intolerant to light (n = 5), intolerant to noise (n = 7), and
blurred vision (n = 2).
Procedure for rating the magnitude of tolerance
Light and sound stimuli of five different intensities were presented
using an IBM-XT personal computer. The computer contained a
parallel interface and controlled both a tone generator (calibrated
for 1000 Hz) with varying amplitude and a 50 W tungsten-halogen
lamp. The tone generator was connected to a pair of ATH-910 ear-
phones (Audiotechnica) with noise-reducing caps. A 50 W incan-
descent lamp was placed on a round tube. The glass-covered aper-
ture (10cm in diameter) was surronnded by a black ring and the
tube was mounted on a mobile and adjustable stand, so as to adjust
the height to the individual patient. The intensities were calibrated
at 1 m distance of the lamp in a room with a background illumina-
tion of 300 Ix.
Five intensities of sound and light were chosen on the empirical
basis that they could be distinguished clearly by the human ear
and eye (57, 71, 81, 89 and 95 dB for sound and 440,500,600, 1000
and 15001x for light). Each of the five intensities was randomly
presented 8 times; there were separate sessions for the two types of
stimuli. Thus, a subject received a total of 40 sound stimuli and 40
light stimuli. Each stimulus was presented for 4 s and was followed
by a constant interval. The rise-fall time of the physical stimulus
was greater than 10 ms. The interval was kept constant in order to
achieve a relative constancy in individual habituation processes
(for sound 6s and for light 12s; see also [3, 15]). During this inter-
val, the subject was asked to evaluate the preceding stimulus on a
7-point rating scale, ranging from totally tolerant/bearable (score:
sO), via very mildly (sl), mildly (s2), moderately (s3), moderately
to severely (s4), severely (s5), to totally unbearable/reduced toler-
ance (s6). The response was given by pressing a button on a 7-
point keyboard. After the session, the median tolerance value per
subject was calculated for each intensity level. These median val-
ues were used for statistical analysis.
Sound
The background levels of noise in the examination room ranged
from 46 to 51 dB. Before putting on the earphones, the subject re-
ceived the following instructions: "You will hear a series of sounds
of varying intensity through your headphones. Each sound will be
presented for 4 s. After the tone has finished, please press the but-
ton on the 7-point keyboard that corresponds to the degree of to-
lerance you have experienced. The left button means that you can
tolerate the sound stimulus; the one of the extreme right means
that you find the sound unbearable. The buttons in-between corre-
spond to a decreasing scale of tolerance from left to right. A new
stimulus will be presented automatically after 6s. Forty stimuli of
mixed intensity will be given at random 2"
Light
The average background illumination in the examination room
was about 3001x. The room had dimmed windows. Each subject
was seated so as to look into the centre of the light source at 1 m
distance from their eyes. The subjects received the following in-
structions: "Look into the centre of the lamp. The lamp will shine
for 4s. You will then have 12s to press a button on the 7-point
keyboard that corresponds to the degree of tolerance you have ex-
perienced. The left button means that you can tolerate the light
stimulus; the one on the extreme right means that you find the
light unbearable. The buttons in-between correspond to a decreas-
ing scale of tolerance from left to right. Each new stimulus will be
presented automatically after 12 s. Forty stimuli of different inten-
sity will be given at random."
Statistical analysis
We first assessed whether there was an overall difference between
the three groups for all the five intensities of light and sound. Be-
cause of the ordinal level of the rating scale, the ranks over all ob-
servations per intensity were calculated [4] and were analysed by
multivariate analysis of variance (SAS) [14]. Then separate analy-
ses per intensity were carried out using Duncan's multiple range
test as a post hoc test to evaluate between-group differences for
significant overall effects. A probability level of less than 0.05 de-
fined a significant difference.
Results
Multivariate analysis of variance yielded a significant
overall effect for tolerance for both sound (Wilk's lamb-
da: F(5.25) = 2.75, P< 0.05) and light (Wilk's lambda:
F(5.25) = 4.10, P<0.001). Post hoc testing indicated
that the MHI patients with PCS tolerated the 71, 81, 89
and 95 dB, and the 500, 600, 1000 and 1500 lx levels sig-
nificantly less well than the patients without PCS and the
non-concussed controls (see also Fig. 1). The patients
without PCS did not have a significantly different toler-
ance from that of the non-injured healthy controls for
any of the intensities, except for a decreased tolerance to
the 600 lx light stimulus.
At an individual level, there were seven MHI patients
with PCS who demonstrated a severely to totally reduced
level of tolerance (tolerance scores of 5-6) to 95 dB com-
pared with one patient without PCS and none of the
non-concussed control subjects. Five patients with PCS
compared with one patient without PCS and none of the
non-concussed control subjects showed severely to to-
tally reduced tolerance to 1500 Ix.
445
Discussion
There has been much debate over the years as to whether
minor head injuries result in significant and persistent
cerebral damage, and if present, whether it is demon-
strable by objective methods. Experimental studies and
human autopsy data have shown that even MHIs may
lead to anatomical abnormalities [2]. However, other
patients may recover quickly and be without symptoms
after a MHI. Although it has been reported that persis-
tent behavioural dysfunction after a MHI is not explicitly
associated with cognitive disability [9, 12], Ewing et al.
[6] provided evidence that persisting cognitive effects
may still be present after a MHI, but only emerge under
the effects of stress.
Jonsson et al. [8] found that MHI patients with persis-
tent PCS at an average of 3 months after injury had a sig-
nificantly lower ability to endure intense sound and light
stimuli than control subjects. The present results indi-
cate that tolerance for light and sound is significantly
decreased in MHI patients with persistent symptoms
6 months after injury compared with the tolerance of
matched patients without PCS and non-concussed con-
trols. With respect to sub-maximal levels of tolerance to
less intense stimuli, MHI patients with PCS were signifi-
cantly less tolerant to low sound (71 dB) and light inten-
sities (500 lx) compared with patients from the two con-
trol groups. This means that, for example, the shining of
a lamp or the noise of a lively conversation could disturb
a MHI patient who has persistent symptoms. Although
patients without PCS did not differ significantly from the
healthy control subjects in their tolerance for light and
sound, there was a very slight tendency to a decreased
tolerance for light.
Waddell and Gronwall [16] found in their study that
all MH! patients with decreased tolerance for sound and
light had evidence of reduced functions of information
processing. Additionally, Jonsson et al. [8] reported that
symptomatic patients had a lowered tolerance for light
and sound stimuli after a MHI than had symptomatic
non-concussed neurotic patients. These findings may
provide evidence for the hypothesis that there is an or-
ganic basis for this type of hyperaesthesia. Nevertheless,
further studies are needed to establish this hypothesis.
Tolerance to light Tolerance to sound
0
6[
[, Patients with PCS
]
, Patients with PCS
5~-r"l Patients without PCS T
I 5
[] Patients without PeS
iI.
Healthy subjects _ / I
4
g g
2 2
'0
0
440 500 600 1000 1500 57 71 81 89 95
Lux Decibel
Fig. 1. Mean levels of tolerance of
the patient and control groups per
intensity (means + SEM are
presented). The 7-point rating
scale ranged from totally tolerant/
bearable (score:s0), via very
mildly (sl), mildly (s2), moder-
ately (s3), moderately to severely
(s4), severely (s5), to totally
unbearable/reduced tolerance (s6)
446
It is possible that the post-traumatic changes in toler-
ance for light and sound are a manifestation of a lack of
inhibitory control by orbital frontal cortex areas over
sensory information processed by posterior brain areas
and subcortical centres [7, 17]. The changes in the visual
and acoustic system following MHI may persist together
with subjective symptoms.
It can be concluded that MHI patients with PCS may
already be disturbed by sound or light intensities com-
mon to daily life up to 6 months after injury, whereas pa-
tients without PCS can normally tolerate more intense
stimuli of sound and light. The present study provides an
objective measure for the assessment of persistent PCS
in uncomplicated MHI patients with no pre-morbid ab-
normalities.
Acknowledgements. The authors thank Marlies Adriaans and Lies-
beth Bloemers for excellent technical assistance.
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