Understanding posttraumatic nightmares: An empirical and conceptual review

Abstract

Posttraumatic nightmares (PTNMs) are a highly prevalent and distressing symptom of posttraumatic stress disorder (PTSD), yet have been subject to limited phenomenological investigation. As a result, the parameters of the symptom required to meet diagnostic criterion for PTSD are unclear and their relationship with normal dreams following trauma is not known. A categorical distinction between PTNMs and normal dreams has been assumed, explicitly within dreaming theories and perhaps implicitly within the PTSD field, but lacks empirical support. This paper reviews the current understanding of PTNMs and normal dreams following trauma within the PTSD and dreaming fields respectively. It is argued that models of PTSD can readily account for repetitive PTNMs that accurately replay the traumatic event, but not those that are symbolic of the traumatic event. On the other hand, theories of dreaming that propose a psychologically adaptive function of dreams can account for both replay and symbolic nightmares that evolve over time, but not those that are stuck in repetition. It is concluded that there is no adequate explanation for the range of dreams following trauma including the PTNM of PTSD that is both symbolic and repetitive. Three alternate explanatory models are proposed that draw on existing knowledge within both the PTSD and dreaming fields to explain the full range of nightmares following trauma.

Introduction

Repetitive and distressing trauma-related dreams are recognised as a core symptom of posttraumatic stress disorder (PTSD) in DSM IV (Criterion B2: “Recurrent distressing dreams of the event”) and ICD 10 (“Persistent remembering of the stressor in recurring dreams”). They have been referred to as a hallmark of PTSD (Hartmann, 1998, Wilmer, 1996). The significance of trauma-related dreams in PTSD is supported by their high prevalence and impact on the sufferer. Six-month prevalence rates in treatment seeking populations of 61% (Kilpatrick et al., 1997) and 67% (Schreuder, Kleijn, & Rooijmans, 2000), and point prevalence rates in a community sample of 25%, second only amongst the re-experiencing symptoms of PTSD to daytime intrusions at 33% (Ohayan & Shapiro, 2000) have been reported. Trauma-related dreams are not only very distressing in their own right (Coalson, 1995), but are associated with frequent nocturnal awakenings (Germain and Nielsen, 2003, Woodward et al., 2000). Beyond the general adverse effect of poor sleep on daytime functioning, Mellman and colleagues (Mellman, 1997, Mellman et al., 2004) have proposed that disrupted sleep in PTSD may prevent the normal and potentially adaptive memory-processing function of REM sleep and thereby have a role in the development and maintenance of the disorder. The importance of increasing our understanding of the trauma-related dreams of PTSD has been highlighted in several recent review articles (Harvey and Jones, 2003, Pillar et al., 2000, Wittman et al., 2007). However the phenomenology of trauma-related dreams remains little understood, with Wittman et al. (2007) concluding that there is “alarmingly little reliable information characterising the phenomenology of the disturbing dream in PTSD”. At the most basic level, there is no apparent consensus on the parameters of the symptom. How distressing, and how trauma-related, do the dreams need to be, to meet criterion?

Of particular importance, from both a theoretical and clinical perspective, is the question of the relationship between the recurrent distressing dreams of PTSD and normal dreams following exposure to a traumatic event. Among the majority of people exposed to a traumatic event who do not develop PTSD, the occurrence of trauma-related dreams is also common in the early aftermath of trauma (Lavie, 2001). Are they a categorically distinct phenomena (for example, a normal dream rather than an intrusive symptom of PTSD) or do they differ only qualitatively along a continuum of dream types? To date these types of dream have been studied independently within the fields of PTSD and dreaming respectively. With different foci of enquiry and research methodologies, little is known about the relationship between them.

Within the PTSD field, these fundamental questions about the nature of posttraumatic nightmares in PTSD are important for a number of reasons. First, more clearly defined parameters of this core symptom of PTSD would help clinicians to distinguish them from normal trauma dreams that are associated with recovery, and thereby improve consistency in assessment and diagnostic practices. Secondly, in a research setting greater specificity about the phenomenon under investigation would improve the methodological rigour of research into the symptom and allow comparisons between studies. Thirdly, if a range of trauma-related dreams that differ in important phenomenological ways can be reliably differentiated, future research may lead to the capacity to predict the course of trauma-related dreams at assessment and recommend optimal intervention tailored to the dream type.

As a first step towards a better understanding of trauma-related dreams in PTSD and their relationship with normal dreams following trauma, this paper will a) summarise the empirical evidence reported in both PTSD and dreaming fields regarding the phenomenology of posttraumatic dreams, b) describe the theoretical understanding of those dreams in both fields, c) consider the extent to which the respective theories can account for the observed phenomena, and d) identify any gaps between observed phenomenology and theoretical explanations. Following this review, and in an attempt to address gaps identified, three alternative models of posttraumatic dreams derived from knowledge across the fields of PTSD and dreaming will be proposed.