The Nightmare Disorder Index: development and initial validation in a sample of nurses (2024)

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Abstract

Keywords: nightmares, psychometrics, nurses, insomnia, health, psychosocial

Introduction

Nightmare disorder, characterized by dysphoric, recurring, well-remembered dreams which result in awakening and are associated with daytime impairment, occurs in 2%–5% of the general population [1, 2] and approximately 30% of psychiatric outpatients [3]. Nightmare disorder can present alone, but is frequently associated with comorbid sleep and/or psychological disorders including insomnia [4], posttraumatic stress disorder (PTSD), depression and anxiety [5, 6]. Nightmare disorder is also associated with increased risk for self-harm, self-directed violence, and completed suicide [7–9]. Despite the severity of nightmare disorder and its sequelae, nightmare disorder is rarely assessed or diagnosed [10], underreported to medical providers, and thus likely undertreated [11, 12].

The lack of a brief, validated assessment tool to assess nightmare disorder according to the Diagnostic and Statistical Manual of Mental Disorders – 5th edition (DSM-5) [13] is one current problem that limits the examination of the occurrence and correlates of nightmares and nightmare disorder. Most studies of nightmares rely on a single questionnaire item about nightmares drawn from questionnaires assessing other constructs (e.g. PTSD). Structured clinical interview [14] is the gold standard for assessing nightmare disorder, but interviews are not always feasible in research settings and rarely do they include this disorder. Therefore, self-report retrospective questionnaires are currently the most common method for assessing nightmares [15]. Although retrospective questionnaires could be subject to recall bias and therefore sacrifice some diagnostic accuracy, they offer several important benefits that are commensurate or superior to other methods (e.g. structured clinical interview, sleep diary). First, retrospective questionnaires are brief, affordable, and easily distributed. Second, retrospective questionnaires can be used to assess relatively longer time periods than may be feasible by prospective measures (e.g. sleep diary) without increasing participant burden. Finally, retrospective questionnaires are able to distinguish nightmare frequency from nightmare distress, which is important given evidence that distress may be the more salient factor in predicting negative outcomes [10, 16].

No validated self-report measure thoroughly assesses nightmare disorder as defined by the DSM-5 [13]. We surveyed the literature to collect the most commonly used validated measures of nightmares, which are presented in Table 1. Unfortunately, extant measures use inconsistent definitions of nightmares and nightmare disorder, which makes comparison across studies difficult [17]. As seen in Table 1, a large majority of the previously created nightmare measures fail to directly asses the chronicity (i.e. the length of time the individual has experienced nightmares) and the ability of the individual to recall the nightmare (a diagnostic criterion for nightmare disorder). Further, none of the nightmare measures identified assessed for all DSM-5 criteria of nightmare disorder (i.e. frequency, intensity, chronicity, recall, sleep disruption, daytime impact) of DSM-5 nightmare disorder.

Nurses may be at increased risk for nightmare disorder due to factors including irregular shift schedules, high stress work environment, and high exposure to trauma, yet little is known about the rate and associated psychosocial factors in this population. Nurses serve as the front line of patient care and thus are by nature frequently exposed to traumatic events (e.g. witnessing serious injury and death) and vicarious traumas [18]. Approximately 5% of the population reports nightmares and the rate of nightmares increase drastically in populations who have experienced a traumatic event (e.g. up to 50% of trauma-exposed adults [19]; approximately 24% of nurses) [20]. In one study, [21] 35% of nurses (N = 332) reported nightmares related to their work experiences on a single-item self-report item, which queried the presence of nightmares related to the job description or environment. Nurses reported triggers associated with nightmares included performing end of life care, feeling overextended, caring for combative individuals, and visualizing open wounds or bleeding [21]. Unfortunately, nightmares in the nurse population are discussed in the literature almost exclusively in the context of PTSD, despite the fact that nightmares are commonly reported among individuals without PTSD. Indeed, one study of N = 173 pediatric acute care nurses found 49% of nurses reported nightmares associated with their work, though only 21% of the sample reported significant PTSD symptoms (91% of whom reported nightmares) [22]. Nightmares are associated with increased suicide risk above the effects of depression and PTSD [7, 8], and frequently persist even after successful treatment for PTSD [23]. Although the two aforementioned studies [21, 22] established an estimate of the rate of nightmares in nurses using a single item measure, to our knowledge, there is no existing estimate of the rate of nurses who meet full criteria for nightmare disorder.

One potential consequence of the lack of a screening questionnaire for nightmare disorder is that little is known about the rate of nightmares and associated psychosocial and sleep factors, especially among nurses. Thus, the aims of the current study were twofold. The primary aim was to report on the development and preliminary validation of the Nightmare Disorder Index (NDI), a brief self-report screening questionnaire for DSM-5 nightmare disorder. The secondary aim was to describe the rate and compare the psychosocial functioning and sleep parameters of nurses with (1) no nightmares, (2) subthreshold nightmare disorder symptoms, and (3) probable nightmare disorder.

Methods

Results

Psychometrics of Nightmare Disorder Index

The NDI total score mean was 4.14 (SD = 2.41) for those with subthreshold nightmare disorder symptoms and 9.24 (SD = 2.62) for those who met full criteria for nightmare disorder based on the NDI. The mean was not calculated for individuals who endorsed no nightmares, as their total score is zero. In the current study, the NDI had good internal consistency (α = 0.80). Inter-item and item-total correlations are shown in Figure 1. Inter-item correlations ranged from r = 0.28 to 0.71, with an average inter-item correlation of r = 0.50. The item-total correlation with the total NDI was highest for the nightmare frequency question (r = 0.85) and lowest for the nightmare impairment question (r = 0.55).

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Figure 1.

Inter-item, item-total, convergent, and discriminant correlations between Nightmare Disorder Index facets and other nightmare and non-nightmare measures. Note: TST, total sleep time; NM, nightmare; NDI, Nightmare Disorder Index; PCL-5, Posttraumatic Stress Disorder Checklist; PSQI, Pittsburgh Sleep Quality Index; rCSM, reduced Composite Scale of Morningness.

See Also

Nightmare Disorder: Symptoms, Causes, Treatment, and Prevention

Correlations to establish convergent validity are shown in Figure 1. In general, the NDI total score had medium to large correlations with averaged 14-day diary (r = 0.37–0.41) and single-item (r = 0.32–0.45) measures of nightmares, demonstrating acceptable convergent validity. The highest correlation for the total NDI score was between the NDI total score and the nightmare item from the PSQI, and the lowest correlation was with the nightmare item from the PCL-5. The correlation between the NDI frequency component and average nightmare frequency on the sleep diary was moderate, as was the correlation between the NDI distress component and nightmare severity on the diary. Correlations to establish discriminant validity are shown in Figure 1. In general, the NDI had small correlations (all rs < ±0.15) with measures of constructs which were not expected to be related to nightmare disorder (i.e. actigraphy-derived total sleep time, mean alcoholic drinks, and chronotype), demonstrating good discriminant validity. The NDI had moderate correlations (rs = 0.22–0.33) with constructs which were expected to be somewhat related with nightmare disorder yet not entirely overlapping (i.e. posttraumatic stress, depression, anxiety, perceived stress).

Results from the principal axis factoring analysis provided evidence for a unitary factor structure after examining each of the factor retention methods listed above. The single factor which was retained, which we named “NDI,” had an eigenvalue of 2.31 and reproduced 33.72% of the variance in the items. Pattern coefficients for all items were in the moderate to high range indicating all items were strongly associated with the extracted factor. See Table 3 for factor structure of the NDI.

Table 3.

Pattern/structure coefficients and extracted communalities for the Nightmare Disorder Index

Item	Factor 1: NDI	h2
1. Frequency	0.62	0.38
2. Awakenings	0.42	0.18
3. Distress	0.75	0.57
4. Impairment	0.53	0.28
5. Duration	0.53	0.28

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Discussion

These findings provide preliminary evidence that the NDI is a brief, reliable, and valid assessment of nightmare disorder, particularly among nurses. The rate of nightmare disorder (7.4%) in the current sample was higher than previous studies of the general population (2%–5%) [1, 2], and much lower than rates previously reported by psychiatric outpatients (30%) [3]. The frequency of nightmare disorders in nurses is expected to be a little higher than the general population, given their stressful working environment, but much lower than an outpatient psychiatric population, given psychiatric symptoms were not a requirement for inclusion in the study. The current study found rates of subclinical or higher nightmare symptoms (51.3%) to be greater than the 35% previously reported by nurses who completed a single-item self-report measure that is likely less sensitive than the NDI [21]. Single item measures, which are common in the nightmare literature, risk misrepresenting the severity and prevalence of nightmare disorder. Additionally, these single items each examine only a single dimension of the nightmare experience (e.g. frequency or distress), which could in part explain why correlations with the NDI, which assesses each of the DSM-5 criterion (i.e. frequency, intensity, chronicity, recall, sleep disruption, daytime impact) for nightmare disorder, were lower than anticipated. In contrast to existing single item measures, the NDI is likely more sensitive and specific for specifically assessing nightmare disorder symptoms, though this will need to be confirmed in follow up studies. The supply of trained nurses is scarce, so a reliable, valid, sensitive and specific nightmare screening measure should be helpful in identifying nurses who might benefit from a brief nightmare specific treatment [55], which in turn might reduce psychotherapy stigma, high turnover, and burnout.

Nightmares (subclinical and probable diagnosis) were associated with significant psychosocial burden across nurses and occurred at a greater frequency in nurses working rotating or night shifts. The severity of nightmare symptoms was related to the severity of the psychosocial burden, such that nurses who had probable nightmare disorder based on the NDI had significantly greater symptoms of depression, anxiety, perceived stress, and PTSD symptoms compared to nurses with subthreshold or no nightmares. Further, a similar pattern was shown for the negative emotionality dimension of personality which may be a contributing factor to this finding. The rate of nightmares and associated psychosocial factors of this population is particularly troublesome given the integral role nurses play in the health care system and warrants further exploration and treatment of nightmares in this population.

Despite a general paucity of research on nightmare disorder in nurse populations, these findings replicate previous research investigating the heightened risk of other mental health symptoms in various domains of functioning for nurses. A sample of pediatric intensive care nurses displayed heightened rates of PTSD (21%), nightmares (49%), anxiety symptoms (16%), depression symptoms (10%), and overall burnout (68%), with approximately 82% of the nurses reporting at least one significantly distressing psychological symptom [22]. Similarly, nurses in acute or critical care experienced elevated rates of PTSD (24%) [20]. One previous study demonstrated approximately 14% of general practice nurses displayed significant PTSD symptoms [20], which is similar to the rate of 11% found in the current study. Although clinically significant PTSD symptoms were significantly higher among those with probable nightmare disorder compared to those with subthreshold or no nightmares, PTSD does not appear to be the sole driver of nightmare disorder reporting in this sample; only a third of those with probable nightmare disorder reported significant PTSD symptoms. The results of this study are consistent with previous research which demonstrates nurses carry a significant psychosocial burden. Given the finding that these psychosocial symptoms increase with the severity of nightmare disorder symptoms, this indicates a need for further research on the detection and treatment of nightmares, particularly for nurses.

Additionally, this study indicated nurses who engage in overnight or rotating shift work experience more severe nightmare symptoms than do those who only work the day shift. This finding is also consistent with previous research that suggests shift workers experience higher rates of parasomnias including nightmares [56]. One hypothesis to explain this relationship between shift work and nightmares is the significant increase in REM sleep during the daytime sleep for shift workers [57]. It is possible that the increase in REM sleep pressure and frequency of interruptions in REM sleep for nurses engaging in regular shift work in turn increases the propensity to experience nightmares [58]. Although examining sleep architecture was outside the scope of the current study, this is an important future direction when considering the mechanisms of increased parasomnias among nurses.

Probable nightmare disorder, and to a lesser extent subthreshold nightmares, were associated with greater subjective number of awakenings and poorer self-reported sleep quality across the 14 days of sleep diary. These results are overall consistent with self-report of nightmare experiences, in which the dreams cause awakenings often paired with heightened physiological arousal (e.g. racing heart, shallow breathing, sweating). Individuals who report difficulty returning to sleep are more likely to form a memory of the awakening and thus individuals who report nightmares may experience their sleep as more fragmented and less restorative. Although groups differed on number of awakenings, they did not significantly differ on wake after sleep onset on the sleep diary. There are several potential explanations for this. First, the WASO was based on two full weeks of sleep diaries. WASO on nights without nightmares might be low or 0, which could lower the mean WASO overall even if WASO is longer on nights with nightmares. Second, examining individual means across the groups reveals about the amount of WASO one would expect given the number of awakenings. By dividing WASO/number of awakenings (NWAK), we see the average length of awakening for the probable nightmare disorder group is 6.6 min, versus 6.1 min for the subthreshold nightmares group and 7.3 min for the no nightmares group. The differences in WASO are small, thus not statistically significantly different, but the magnitude of differences is unsurprising in the context of the relatively small group differences in NWAK. Third, WASO and NWAK are not necessarily highly related. Individuals with nightmares could wake frequently, but briefly, which would demonstrate high NWAK but low WASO. Alternatively, individuals with insomnia could wake only once or twice in the night but be awake for a longer period of time, which would demonstrate NWAK but higher WASO. It appears that individuals with nightmares in this sample fell more into the former category rather than the latter.

There were no significant differences between groups (i.e. no nightmares, subthreshold nightmare symptoms, probable nightmare disorder) for any actigraphy-derived sleep parameters. Actigraphy tends to have low specificity to detect wakefulness among sleep-disordered populations [59], but it is surprising that differences did not arise given the nature of nightmare awakenings is likely to induce significant movement. It is possible that 14 days of actigraphy was not long enough to detect differences between groups given that someone may experience nightmares once a week or once a month and still qualify for a diagnosis of nightmare disorder. Previous studies similarly have shown that individuals with frequent nightmares report poorer subjective sleep quality, more waking problems, and more severe insomnia symptoms, but no differences in overall PSG sleep architecture [26]. The current study reveals nightmares and probable nightmare disorder primarily impact number of awakenings and perceived quality of sleep. More research is needed using a comprehensive measurement strategy to better understand the impact of nightmares on sleep.

The current study presents with a variety of strengths and fills an important gap in the understanding of nightmare disorder. To date, we are unaware of any studies that estimate the rate of DSM-5 criteria nightmare disorders in nurses. Given the well documented deleterious implications of nightmare disorder (e.g. increased symptoms of depression, anxiety, burnout), this knowledge of nightmare disorder prevalence is important to the mental health of nurses as well as their job satisfaction and performance. Given the integral role nurses play in the health care system, this is beneficial to not only nurses themselves but also to society. Additionally, this study provides the first brief assessment for DSM-5 defined nightmare disorder. As indicated in Table 1, although various nightmare questions exist, they often do not assess important domains of the nightmares (e.g. recall, sleep/wake impact) or are possibly burdensome for the participant/patient to complete (e.g. 30 items). The NDI fills this gap in sleep disorder assessment by providing a psychometrically sound, 5-item assessment for DSM-5 nightmare disorder that can be used as both a continuous measure of nightmare severity and a categorical measure of nightmare disorder.

While the current study demonstrated many strengths, it is also important to address its shortcomings. One limitation of the current study was the lack of a full-length nightmare measure and a structured clinical interview to compare with the NDI. However, given the participant burden in the parent study, it was not possible to add measures above and beyond those reported here. That said, this is one of the few studies to compare the frequency and severity of nightmares with 14 daily sleep diaries. An additional limitation was that, in the parent study, the NDI was not given to assess the same time period as the 14-day sleep diary completed by participants. Due to this, it is possible the correlations between the NDI and sleep diary outcomes were slightly attenuated, as nightmares do not necessarily present consistently across weeks. It is possible that our relatively small samples size and limited recruitment sites (i.e. two hospitals) provided limited power to detect differences in some measures such as actigraphy outcomes. However, as shown in Table 1, ours is among the largest validity studies of a nightmare assessment tool to date.

Finally, it is important to point out the limitations of the NDI itself as a brief screening measure. Per the DSM-5, nightmare disorder which occurs solely in the context of PTSD does not necessitate an independent diagnosis; thus, the NDI should be used with caution in populations with high risk of PTSD. Beyond this consideration, the NDI is a brief screening measure and should not be used to assign a definitive diagnosis of nightmare disorder. Rather, it should be used to indicate probable nightmare disorder which could be confirmed by clinical interview. This is made especially salient by the overlap (i.e. small to medium correlations) between the NDI and other measures of psychiatric symptoms, particularly depression It is also important to note that the DSM-5 does not indicate the minimum frequency of nightmares necessary in order to assign a nightmare disorder diagnosis in the criteria (although DSM-5 does specify that severity can be classified as mild [less than one episode per week on average], moderate [one or more episodes per week but less than nightly], or severe [episodes nightly]). In the current study, we used a minimum cutoff of 1×/month in order to maximize detection of potential nightmare disorder with this brief screening measure. If researchers prefer to use a higher minimum frequency (e.g. 1×/week) the measure can be used in that manner, although the validation results presented here may not translate. However, given all of the limitations mentioned above, the NDI does appear to be a more valid and reliable measure of probable nightmare disorder than the previous penchant for using single items from other questionnaires, and we hope future epidemiological and treatment studies will transition to the more precise NDI.

To address these limitations, further investigation is warranted. Primarily, additional validation of the NDI in a variety of populations and contexts would continue to strengthen the evidence for its utility in screening nightmare disorder. A study comparing participant responses on the NDI to a clinical interview would provide important information on the validity of this measure and its ability to reliably identify nightmare disorder. Additionally, given that the NDI has only been preliminarily examined in nurses, it is important that future research explore its utility in a variety of populations (e.g. primary care, military, undergraduate students) and in a variety of settings (e.g. outpatient, online) to determine the generalizability of the assessment.

As previously indicated by Nadorff et al. [11], the experience of nightmares is often underreported and seen by patients as untreatable. Their study indicates approximately 62.2% of adults and 88.9% of undergraduate students with clinically significant nightmares reported they have not discussed these nightmares with a healthcare provider. This severe lack in reporting clinically significant symptoms is further exacerbated by a lack of screening for nightmares by healthcare providers. All these factors taken together leads to an underutilization of evidence-based nightmare treatments. Provided the psychosocial consequences of nightmare disorder, this low rate of detection and treatment is both individually and societally significant. Overall, this study continues to emphasize a need for further assessment and treatment of nightmare disorder, particularly in nurses.

Preliminary results indicate the NDI is an efficient and clinically useful screener for nightmare disorder as defined by the DSM-5. Given this, the NDI provides a brief assessment tool for both researchers and clinicians to screen for clinically significant nightmare disorder in their participants and patients. Hopefully, through increased assessment for nightmare disorder, a parallel increase in the utilization of evidence-based treatment for nightmares [55] (e.g. imagery rehearsal therapy or exposure, relaxation, and rescription therapy) will be observed.

Supplementary Material

Acknowledgments

This research supported by National Institute of Allergy and Infectious Diseases grant 1R01AI128359-01. We would like to thank the nurse PIs, the participants, and the research assistants for their help facilitating this study.

Disclosure Statement

Financial disclosure: This research was supported by National Institute of Allergy and Infectious Diseases (grant 1R01AI128359-01).

Non-financial disclosure: None.

References