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Nightmare Frequency in Patients with Primary Insomnia
International Journal of Dream Research Volume 2, No. 2 (2009) 85
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Nightmares are dened as disturbing mental experiences
that generally occur during REM sleep and that often result in
awakening (ICSD-2, American Academy of Sleep Medicine,
2005). Nightmares are very common; up to 80 % of adults
reported that they had occasionally experienced night-
mares (Englehart & Hale, 1990; Schredl, Morlock & Bozzer,
1996). Representative studies indicate that about 5% of the
general population has a current problem with nightmares
(Bixler et al., 1979; Cirignotta et al., 1983, Stepansky et al.,
1998). The etiology of nightmare is modeled by a disposi-
tion-stress model. Research indicates that genetic factors,
(Hublin et al., 1999), as well as current stressors, (Schredl,
2003; Schredl et al., 2008), are related to nightmare frequen-
cy. Since stressors, for example negative live events, are
also of importance in the etiology of primary insomnia (e.g.,
Harvey, 2002), it seems logical to hypothesize that these pa-
tients should experience nightmares more often than per-
sons without insomnia. Where as the relationship between
insomnia symptoms like frequency of nocturnal awakenings
and nightmares have been shown in a large number of stud-
ies (e.g., Charney et al., 1977; Krakow et al., 1995; Ohayon,
Morselli & Guilleminault, 1997; Schredl, 2003), Ohayon et
al. (1997) stated that the prevalence of primary insomnia
were lower in the patients having nightmares compared to
the patients with insomniac complaints and no nightmares.
In this study, the occurrence of nightmares was related to
depression and anxiety disorders; both mental disorders
are often accompanied by sleep disorders. The result of el-
evated nightmare frequency in insomnia patients reported
by Hoffmann et al. (1996) can also be interpreted in that way
because their sample included patients with primary insom-
nia and patients with secondary insomnia due to a mental
disorder. On the other hand, several studies (Schredl, 1991;
Ermann, 1995; Schredl et al., 1998) demonstrated that pa-
tients with primary insomnia reported more negatively toned
dreams in comparison to healthy controls.
The aim of the present study was to compare the nightmare
frequency of patients with primary insomnia (diagnosed in a
sleep clinic in order to rule out other causes for the insomnia
symptoms) with persons without insomnia. The second aim
was to determine whether nightmare frequency was related
to severity of the insomnia complaints.
Method1.
Participants1.1.
Patients. 295 patients (178 women, 117 men) diagnosed for
primary insomnia both by polysomnographic recording of
their night sleep and by psychiatric interviews were included
in the study. Common diagnostic criteria (DSM IV, American
Psychiatric Association, 1996; ICD 10, Deutsches Institut
für Medizinische Dokumentation und Information, 1994;
ICSD-2, American Academy of Sleep Medicine, 2005) were
applied. Patients with diagnosis of mental disorders such
as major depression, dysthymia or anxiety disorder were
excluded. Sleep apnea and periodic leg movements were
ruled out by measuring nasal and oral airow, chest and ab-
domen movements, blood oxygen saturation and anterior
tibialis electromyogram in both legs. The patients mean age
was 45.8 ± 14.9 yrs.
Healthy controls. The sample included 444 persons whose
mean age was 23.5 ± 5.7 years. These 376 women and 68
men were mainly psychology students. The participants
were recruited at the Universities of Mannheim, Heidelberg,
and Landau for a study entitled “Sleep, dreams, and per-
sonality” (Schredl et al., 2003). Participants were paid for
participation.
Research instruments1.2.
The LISST sleep questionnaire (Landecker Inventar zur Er-
fassung von Schlafstörungen; Schürmann et al., 2001) is
comprised of 75 items and was constructed as a screening
instrument to detect different sleep disorders. Sum scores
Nightmare Frequency in Patients with Primary
Insomnia
Michael Schredl
Central Institute of Mental Health, Mannheim, Germany
Coresponding address:
Prof. Dr. Michael Schredl, Sleep laboratory, Central Institute of
Mental Health, PO Box 122120, 68072 Mannheim, Germany.
Email: Michael.Schredl@zi-mannheim.de
Submitted for publication: February 2009
Accepted for publication: March 2009
Summary. The present study investigated the nightmare frequency of patients with insomnia. Patients reported night-
mares more often, especially when overall dream recall frequency was statistically controlled. Moreover, nightmare fre-
quency was related to the severity of insomnia. It would be interesting to study whether specic techniques for treating
nightmares (for example; imagery rehearsal therapy) are benecial for insomnia patients with nightmares.
Keywords: Nightmare; Insomnia
Nightmare Frequency in Patients with Primary Insomnia
International Journal of Dream Research Volume 2, No. 2 (2009)86
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were computed for self-reported symptoms of insomnia (6
items), nocturnal breathing disorders (4 items), restless legs
syndrome (5 items), daytime tiredness (5 items), sleep qual-
ity (8 items) and disturbances of the sleep/wake rhythm.
The single scales followed a six-point Likert scale format
(1 = never, 2 = rarely, 3 = sometimes, 4 = often, 5 = very
often, 6 = always). The item measuring nightmare frequency
was also of this six-point scale format. Sufcient internal
consistencies as well as accurate discrimination of patients
with sleep disorders (diagnosed in sleep medicine centers
including two polysomnographic procedures) have been
demonstrated (Schürmann et al., 2001). For eliciting dream
recall, a seven-point dream recall frequency scale (coded
from 0 = never, 1 = less than once a month, 2 = about once
a month, 3 = two or three times a month, 4 = about once a
week, 5 = several times a week, and 6 = almost every morn-
ing) was included in the sleep questionnaire. The dream
recall frequency scale has a high retest reliability (r = .85;
Schredl, 2004).
Procedure1.3.
The patients completed the LISST sleep questionnaire prior
to their rst diagnostic interview in the outpatient sleep cen-
ter. Subsequently, they spent two consecutive nights with
standard polysomnographic recordings (EEG, EOG, EMG,
ECG, respiratory parameters, blood oxygen saturation and
anterior tibialis EMG) in the sleep laboratory.
Statistical analyses included ANCOVAs and regression
models in order to control for age and gender (because age
and gender distributions differed between the patient group
and the healthy controls).
Results2.
Nightmare frequency2.1.
The comparison between patients with insomnia and
healthy controls in terms of nightmare frequency is depicted
in Table 1. Although the mean difference is not large, the
statistical analysis (ANCOVA with the factors diagnosis and
gender and the covariate age) yielded a signicant differ-
ence between insomnia patients and controls (F = 7.3, p =
.0070) after controlling for gender (F = 4.5, p = .0341) and
age (F = 2.8, p = .0958). The mean difference is larger for
men (see Table 1) but the interaction term of the ANCOVA
did not reach signicance (F = 2.2, p = .1361). Interestingly,
the statistical analysis showed that the difference between
insomnia patients and healthy controls regarding nightmare
frequency is even more pronounced (F = 17.8, p < .0001) if
dream recall frequency is statistically controlled (added as
second covariate).
Factors related to nightmare frequency2.2.
Nightmare frequency was not related to age, gender and
sleep quality. On the other hand, complaints regarding in-
somnia symptoms, restless legs symptoms, apnea symp-
toms, sleep/wake rhythm disturbances and daytime tired-
ness were positively correlated with nightmare frequency.
As expected, the correlation between nightmare frequency
and dream recall frequency was quite high. The regression
analysis explained 24.5 % of the variance (F = 10.4, p <
.0001) and indicated that insomnia symptoms as well as
apnea symptoms were the factors most closely associated
with nightmare frequency (in addition to dream recall fre-
quency which was introduced as a control variable).
Discussion3.
The results indicate that, as predicted, insomnia patients
report nightmares more often than controls, conrming the
ndings of more negatively toned dreams in these patients
(e.g., Schredl et al., 1998). This difference is even more
pronounced if dream recall frequency was statistically con-
trolled, i.e. the percentage of negatively toned dreams in re-
lation to the total number of recalled dreams is larger in the
patient group. In addition, nightmare frequency was related
to the severity of insomnia symptoms. To carry on this line
of research, it would be interesting to study whether the oc-
currence of current stressors solely explain the heightened
nightmare frequency in insomnia patients. Schredl (2003)
reported that although stress reduced the correlation coef-
cients between sleep quality and nightmare frequency the
correlation coefcient was still signicant. The interaction
between nightmares and insomnia symptoms can be two-
fold. First, the nightmare is, by denition, interrupting sleep
and thus increases insomnia symptoms (nocturnal awak-
enings). Second, fears that nightmares might occur during
the night impairs sleep onset and may lead to light sleep. It
would be interesting to study insomnia patients with night-
mares in the sleep laboratory in order to determine whether
the increased number of insomnia complaints is reected in
altered sleep physiology, i.e. number of brief awakenings or
arousal indices.
The signicant relationship between nightmare frequen-
cy and apnea symptoms is in line with previous research
(Hicks & Bautista, 2003; Schredl, 2008).It should be kept in
mind that sleep apnea as possible co-morbid sleep disor-
der was ruled out in this patient group. Moreover, two stud-
ies (Schredl et al., 2006; Schredl & Schmitt, 2009) clearly
demonstrated that sleep apnea patient do not report night-
mares more often than healthy controls. The hypothesis put
forward by Boerner (1855) that breathing pauses accom-
panied by oxygen desaturations cause nightmares is very
Table 1. Nightmare frequency and dream recall frequency of patients with insomnia and healthy controls (Means ± SD)
Variable Insomnia patients Healthy Controls
Nightmare frequency (Total sample) 2.39 ± 1.36 2.30 ± 1.10
Nightmare frequency (women) 2.41 ± 1.33 2.36 ± 1.10
Nightmare frequency (men) 2.36 ± 1.41 1.94 ± 1.01
Dream recall frequency (Total) 2.99 ± 1.91 4.31 ± 1.21
Nightmare Frequency in Patients with Primary Insomnia
International Journal of Dream Research Volume 2, No. 2 (2009) 87
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unlikely to be valid. So, future research has to investigate
whether breathing pauses, measured by polygraphy (am-
bulatory measurement unit) or polysomnography (sleep
laboratory), occur more often in persons with nightmares;as
a link between dream content and sleep physiology (body-
mind interaction, see Erlacher & Schredl, 2008),or whether
the subjective reporting of apnea symptoms are related to
the nightmares directly, i.e. waking up from a nightmare and
having the impression of gasping for air.
The correlation between nightmare frequency and day-
time tiredness reects the negative effects nightmares exert
on the next day (e.g., Köthe & Piotrowski, 2001). Also war-
ranting further investigation, is why restless legs symptoms,
as well as complaints regarding the sleep/wake rhythm, are
related to nightmare frequency (at least in the correlation
analyses)..
To summarize, nightmare frequency was elevated in in-
somnia patients and related to the severity of insomnia
symptoms within the patient group. From a clinical view-
point, it would be very interesting to study whether imagery
rehearsal therapy (Krakow & Zadra, 2006) which has been
shown to reduce nightmare frequency effectively is also
benecial for insomnia patients with additional nightmare
complaints. The brief intervention can easily t into the stan-
dard cognitive-behavioral therapy for insomnia.
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Variable Correlation coefcient Standardized Regression coef-
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Age -.093 .047
Gender (1 = female, 0 = male) .039 .014
Restless legs symptoms .155 ** .025
Insomnia symptoms .285 *** .250 ***
Apnea symptoms .156 ** .167 **
Sleep/wake rhythm disturbances .190 ** .013
Sleep quality .023 -.167
Daytime tiredness .206 *** .102
Dream recall frequency .428 *** .379 ***
Note. * p < .05, ** p < .01, *** p < .001
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