Department of Histopathology, Manchester Royal Infirmary, UK
Department of Histopathology, Manchester Royal Infirmary, UK and Laboratory Medicine Academic Group, University of Manchester, UK
Correspondence: Ray McMahon, Manchester Royal Infirmary, Oxford Road, Manchester MI3 9WL, UK. E-mail: ray.mcmahon{at}man.ac.uk
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ABSTRACT |
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Aims To ascertain whether brain weight is different in people of a younger age who commit suicide than in those who die accidentally.
Method A retrospective review of post-mortem reports collecting height, weight and brain weight in 100 suicide victims (87 males, mean age 38.5 years) and 100 age/gender-matched controls who died accidentally or of natural causes (87 males, mean age 38.7 years). Comparison by t-test was made of brain weight in isolation as well as brain weight corrected for height, weight and body mass index.
Results These results reveal no significant difference in brain weight in suicide cases compared to the general population (P > 0.05). The brain weight of those who died by hanging was significantly higher than of those who died by overdose.
Conclusions Whatever the significant neuropsychiatric elements are that influence suicidal behaviour, they do not consistently affect brain weight in the population studied.
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INTRODUCTION |
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Following the findings of Salib & Tadros (2000) we thought that it would be valuable to look at brain weight in suicide in a wider age range and also to compare suicide victims with those who died both accidentally and of natural causes. This would allow us to ascertain whether there was a difference in brain weight between those who have suicidal intent and those who do not. Methods of suicide could also be compared to see if these altered brain weight.
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METHOD |
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Comparison of data
Average brain weight in each group was then compared. Body mass index
(BMI), defined as weight (in kg)/height2 (m2) was
calculated and a comparison of the brain weight/BMI was made in the cases and
controls. The ratios of brain weight/weight and brain weight/height were also
compared. Standard deviation (s.d.) and 95% confidence intervals were
calculated for each of these parameters. Mean differences were calculated and
a paired t-test was used to ascertain whether the difference was significant.
This was carried out for the entire casecontrol group but also
separately for the two main modes of suicide, hanging and overdose. Analysis
could not be performed on the other modes as the sample sizes were too small.
Cases of death by accidental excess substance ingestion were also analysed
separately. They were compared with both suicide cases and death by natural
causes to assess whether there was any difference in brain weight depending on
whether death was natural or unnatural, and whether unnatural death was
intentional or accidental. Suicide cases were also compared to the
natural-causes-only (excluding accidental overdose) group and the major
subgroups of the suicide cases were compared to ascertain the effect of the
method of death on brain weight.
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RESULTS |
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Brain weights
Average brain weight in suicide cases was 1449 g (s.d. 161 g) compared with
1423 g (s.d. 161 g) in the control group. Average brain weight in males was
1468 g for suicide victims and 1449 g for the controls. In females, the
average brain weights were 1251 g for suicides and 1322 g for the controls.
BMI was calculated in the standard manner, giving values of 22.24
kg/m2 for cases and 21.74 kg/m2 for controls. Thus, when
brain weight was compared to BMI, the result in suicide victims was 67.37
g/kg/m2 (s.d. 14.1) and 68.1 g/kg/m2 in the control
group (s.d. 15.3). Mean brain weight/body weight was 21.2 (s.d. 4.12) in cases
and 21.8 (s.d. 5.00) in controls. Mean brain weight/height was 813 g/m in
cases (s.d. 76.4) and 805 g/m (s.d. 85.1) in controls. The same calculations
were performed for the male cases and controls only to exclude bias due to the
lower average brain weight in females seen both in this study and in published
data (Knight, 1996). These data
are summarised in Table 3 and
the data for brain weight controlled for BMI are shown in
Figure 1.
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Comparison of suicide victims and control group
Comparing brain weights gave a mean difference of 25.71 g (i.e. on average
the brain weight in suicide victims was 25.71 g heavier) with an s.d. of 193.4
g (P=0.187). Similarly, the differences between the brain weights controlled
for BMI was 0.70 (s.d. 19.9, P=0.727). Brain weight corrected for weight gave
a difference of 0.61 g/kg (s.d. 6.79, P=0.368). Brain weight corrected for
height gave a mean difference of 8.45 g/m (s.d. 109, P=0.441). There were no
significant differences between hangings and overdoses compared with natural
deaths, or related to the chosen method and dying accidentally, or between
suicidal and accidental overdose.
Comparison of those who committed suicide by hanging and
overdose
However, when hanging victims were compared with those having deliberately
overdosed, the difference in brain weight was 92 g (i.e. the brain in hanging
was 92 g heavier than that in overdose). This was significant with a P value
of 0.006. Controlled for BMI, the difference was 11.4 g/kg/m2
(P<0.001) and the difference controlled for total body weight was 2.51 g/kg
(P=0.004). The difference controlled for height was 29.0 g/m, but this was not
significant. The comparison between hanging and deliberate overdose remained
significant when this sample was confined to the males only. In this instance,
difference in brain weight was 78 g (P=0.047). Controlled for BMI, the
difference was 8.53 g/kg/m2 (P=0.013) and for weight, 2.14 g/kg
(P=0.034). The brain weight to height difference was 33.0 g/m, again not
significant. The results for the subgroups (corrected for BMI) are shown in
Table 3.
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DISCUSSION |
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These results show a slightly different picture to those of Salib & Tadros (2000). However, the parameters of the current study are also slightly different. We have used natural and accidental deaths as controls to ascertain whether those with suicidal intent have different brain weights to those who do not, and these data would suggest that there is no significant difference between these groups. There could be reasons why brain weight in the older population is higher in suicide victims, such as the presence of preclinical dementia in the control group, which would impair the ability to plan and carry out a suicide attempt. There is also a difference in the ages of patients in our group, with only 6% being over 60 years old.
Differences in brain weight between methods of suicide
Because the brain on average weighs 1.4% of the total body weight, we felt
that brain weight looked at in isolation might give misleading results. We
have attempted to avoid any bias by looking at brain weight in relation to
height, weight and BMI. However, there was no significant difference between
the study and control groups. We also compared the results for the different
methods of suicide used. It must be noted that the numbers for drowning (three
people), carbon monoxide poisoning (two people) and train collision (one
person) are very low and no attempt at statistical analysis has been attempted
for these methods. More cases were available for the hanging and overdose
groups and our results suggest that the brain weight in hanging is higher than
that in overdose. If this difference in brain weight had been because of
pre-mortem changes one would expect to see a significant difference for all
modes of suicide. Therefore, we suggest that the observed difference results
from congestion and oedema occurring during the act of hanging itself rather
than a structural difference in the brain before a successful suicide
attempt.
Possible confounding factors
Of course, there is the potential for several confounding factors. In the
elderly population, degenerative brain diseases are more prevalent. In the
younger group, it was difficult to collect a control population who died of
completely natural causes, and even of those who do, the potential effect of
disease on brain weight is unknown, although presumed to be slight. In the
case of unnatural deaths (accidental overdoses and road traffic accidents), we
do not know the effect of mode of death on brain weight. Many brains show a
degree of hypoxic damage, which is probably an agonal event.
Future developments
Salib & Tadros (2000)
recommended establishing a national database of findings following routine
neuropathological examination of autopsy. In the current climate in autopsy
pathology, this will require close cooperation between clinicians and
pathologists to ensure that properly informed consent is obtained from
relatives, notwithstanding the fact that the majority of autopsies in the
context of suicide are performed within the coronial system. However, much
useful information has been and can be gained from detailed structural and
neurochemical studies of brains removed at autopsy from a range of psychiatric
conditions, including those leading to suicide. Although the current study
indicates that there are no differences in brain weight in a younger group of
suicides (compared with the findings of
Salib & Tadros, 2000), this
should not prevent further studies on brains from this group of
individuals.
From our investigations, it would appear that whatever makes a person decide to take their own life does not appear to be related to the weight of the brain.
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Clinical Implications and Limitations |
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LIMITATIONS
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ACKNOWLEDGMENTS |
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Received for publication July 24, 2001. Revision received February 7, 2002. Accepted for publication February 7, 2002.