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Prevalence & Comorbidity of Hallucinations
Last edited |
10/21/2008
Based upon the literature review, it appears clearly that the prevalence of reported hallucinations has
rarely been assessed in the general population
Furthermore, the association between hallucinations and their causes namely
organic pathologies and psychoactive substances was never explored in
subjects of the general population.
Consequently, we plan a study:
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to provide data on the prevalence of
hallucinations in the general population of three European countries;
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to
describe their comorbidity with organic diseases, mental disorders and psychoactive
substances use.
The purpose of this study was:
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to provide additional data on the prevalence
of hallucinations in the general population of three
European countries,
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and to study their association with organic
diseases, mental disorders and psychoactive substances use.
Research
The samples are comprised of respondents from three countries:
the United Kingdom, Germany and Italy.
The participation rate was:
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79.6% (4,972 of 6,249 eligible individuals)
in the UK;
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68.1% (4,115 of 6,047 eligible individuals)
in Germany;
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and 89.4% (3,970 of 4,442 eligible
individuals) in Italy.
Overall, 13,057 subjects participates in the studies.
This sample is representative of 158,690,882 inhabitants.
The overall participation rate was 78%.
Results
Aside from psychotic disorders, many other
conditions may trigger hallucinatory phenomena, namely, use of
drugs such as cocaine and opiates, brainstem pathology,
neurological diseases and other mental disorders such as mood
disorders.
Certain hallucinations can be considered normal
phenomena.
This is the case for hypnagogic and hypnopompic
hallucinations: They were unrelated to any of these pathologies
in about half of the cases.
For individuals who are
frightened by their hypnagogic hallucinations, the risk of a
concomitant mental disorder is four times as high and the risk
of narcolepsy is six times as high as in the remaining sample.
To limit problems related to the inquisitive
nature of the questions about private feelings or perceptions,
the questionnaire was quite extensive to ensure a smooth
progression of the investigation in order to avoid an unexpected
termination of the interview and to allow the differentiation
between illusions and hallucinations; and the identification of
mental organic and toxic disorders that may be responsible for
the hallucinatory phenomena.
Factors related to hallucinations
The results of this study show that:
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2% of the
sample reported having frequent daytime hallucinations (visual,
auditory, olfactory, haptic or gustatory hallucinations, or
out-of-body experiences) and
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16.3% infrequent daytime
hallucinations (less than once a week).
Proportions were
comparable across the three countries.
Use of drugs (opiates, cocaine, amphetamines,
etc.) was significantly associated with almost all the types of
hallucinations investigated, with the exception of auditory
hallucinations. Haptic and gustatory hallucinations were
significantly associated with the use of hypnotic medication.
More specifically, gustatory hallucinations were more prevalent
among respondents who took zopiclone. One of the main side
effects of this hypnotic is the impression of a strange or a
metallic taste in the mouth. Haptic hallucinations, instead,
were associated with hypnotics as a whole.
Clearly, hallucinations affected individuals with
a mental disorder more often than those without. About one third
of mentally disordered respondents had experienced infrequent
hallucinations and about 12% reported having them at least on a
weekly basis. Similarly, respondents with an organic disease
were more likely than others to report hallucinations.
The risks factors for hallucinations identified
in this study are similar to those reported in clinical studies.
Accordingly, use of drugs such as cocaine or opiates is a
significant risk factor for virtually all type of
hallucinations, especially for visual and tactile hallucinations
that are frequent in the case of intoxication. Similarly,
auditory hallucinations have been reported relative to alcohol
withdrawal. Psychotic disorders were significantly associated
with auditory, haptic and visual hallucinations, which are the
three most common forms of hallucinations in psychotic patients.
Significance of hypnagogic and hypnopompic
hallucinations
Hypnagogic hallucinations were very frequent
(24.8%) in this sample, but can be considered non-pathological
in most cases (Ohayon et al., 1996).
We frequently found
frightening hypnagogic hallucinations associated with
narcolepsy.
Hypnagogic and hypnopompic hallucinations need to be
differentiated from other types of hallucinations in the sense
that they occur solely in the transitional period from wake to
sleep (hypnagogic) or from sleep to wake (hypnopompic).
Most
individuals who experience these hallucinations know that the
perception is not true. However, if an individual is terrified
by what he perceives, he may attempt to escape the hallucination
and severely injure himself or others.
Furthermore, there are
case reports in the literature of narcolepsy being misdiagnosed
as a psychotic disorder (Douglass et al., 1991; 1993; Shapiro &
Spitz, 1976).
This may occur if an individual complains only of
frightening hypnagogic hallucinations. Moreover, as sudden sleep
episodes occur in the daytime and are often preceded by
hypnagogic hallucinations, distinguishing between the two
diagnoses can be difficult.
The hallucinations of psychotic
individuals occur at any moment of the day, including at sleep
onset.
It is important, therefore, to ensure that hallucinatory
phenomena occur outside of sleep onset periods in order to rule
out narcolepsy.
The presence of hallucinations is not equivalent
to schizophrenia.
Life conditions such as sensory or sleep
deprivation and even stress can trigger these phenomena.
Hallucinations are a symptom of a psychotic disorder only when
individuals firmly believe them to be true despite what the
people around them say.
On a theoretical point of view, someone could ask
whether hypnagogic and hypnopompic hallucinations are true
hallucinatory perceptions.
In our opinion, they are, even if
their frequency relates them more to a dreamy state than to a
pathological condition.
The main difference between hypnagogic,
hypnopompic and visual or auditory hallucinations relies on the
significance the individual gives to the perceptual phenomenon:
following the hallucinatory experience, a subject with
hypnagogic or hypnopompic hallucinations knows, in most of
cases, that the perceived object did not exist.
In psychotic
individuals, the hallucinations become the reality and are
integrated as such: the interpretations about their meaning
reinforce the pathological character of the hallucination.
Significance of olfactory and gustatory
hallucinations
Olfactory and gustatory hallucinations also pose
a problem.
They are rather a strange perception that is often
not associated with a pathological interpretation.
As our
results show, they are frequently associated with the use of
psychoactive substances such as street drugs (cocaine,
amphetamines, opiates, etc.), alcohol and medication.
Therefore,
we can understand these types of hallucinations rather like a
pathological effect on the sensory organ itself.
Although we
have found psychiatric disorders associated with these types of
hallucinations, the first question to ask is how many of these
psychiatric subjects also received a treatment that could
explain the hallucinatory phenomena.
For some drug users,
olfactory and gustatory hallucinations could be rather a dysosmia or a dysgeusia.
Furthermore, haptic, gustatory
hallucinations and out-of-body experiences are difficult to
distinguish from illusions.
In visual and auditory
hallucinations, other individuals may witness the presence or
absence of the hallucinatory phenomenon.
In the other types of
hallucinations, the hallucinatory character relies on the
description and on the interpretation given to this experience.
In conclusion, hallucinations are symptoms
involved in many fields of pathology.
Where mental disorders are
concerned, they are at the root of delusional themes. They can
also be specific to certain types of drugs or neurological
diseases.
This study showed that the prevalence of
hallucinations in the general population is not negligible.
Content of this page is extracted from
Ohayon MM. Prevalence of hallucinations and their pathological
associations in the general population.
Psychiatry Res. 2000 Dec 27;97(2-3):153-64.
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