Medicolegal aspects of complex behaviours arising from the sleep period: A review and guide for the practising sleep physician

Summary

This review is aimed at summarizing the current state of knowledge regarding parasomnias, which have been implicated in medicolegal cases as well as providing guidance to those working within common-law jurisdictions regarding the technical aspects of the law. Sleepwalking and sexsomnia as a defence are being raised more frequently in criminal cases and there has been public debate on their validity. Unfortunately, expert evidence on forensic sleep disorders continues to be heavily opinion-based with the potential for miscarriages of justice seen in recent highly publicized cases. There is an apparent inertia in research into violent sleep disorders. We review the current state of forensic sleep science in the United Kingdom (UK) and abroad and discuss the need to formulate guidelines based on available evidence. We also highlight the pressing necessity for more research in this area as well as the need to reform the law, which is the subject of a recent Criminal Law Commission report in the United Kingdom. In time, this will facilitate the efficient, proportionate, and just disposal of violence arising from sleep, thus benefitting both society and the individual sufferer.

Introduction

“In all of us, even in good men, there is a lawless wild-beast nature, which peers out in sleep.” Plato “The Republic” Book IX, 571d

The implications of an incorrect diagnosis of either a non-rapid eye movement (non-REM) sleep disorder or rapid eye movement (REM) behaviour disorder to explain criminal behaviour are significant. On the one hand, the guilty or potentially dangerous may go free. On the other, an individual, whose only guilt lies in having an easily managed illness, may be incarcerated. There have been great advances in sleep medicine in the last decade – electroencephalography (EEG) monitoring of sleep, sophisticated imaging techniques and the recognition that psychiatric co-morbidities may influence sleep quality, sleep patterns and manifestations of parasomnias. However, whether a criminal act has occurred as a result of a parasomnia or arisen out of sleep is difficult to prove after the event – the circumstances can never be reliably reproduced.

There is an urgent need to critically re-examine legal perspectives on behaviours occurring during sleep which continue to be grounded in assumptions and decisions from the late 19th and early 20th centuries. These legal doctrines are increasingly out of step with our knowledge of the pathophysiology, treatment modalities and differential diagnosis of these disorders.

In this paper, we present a brief summary of legal definitions invoked in forensic acts performed during sleep or as a result of a sleep disorder. We focus particularly on the dearth of evidence to support both medical and legal decisions in this area. We aim not to review the forensic sleep cases in the literature, but rather raise points of discussion highlighting the problems with post-event testing and problems with proving a sleep defence.

Unfortunately, little original research is being done in this area [1]. Certain cases are reported over and over again in the literature and only a few centres in the world are undertaking limited studies in the field. Case reports tend to only expand the possibilities for forensic sleep behaviour, when what is arguably needed is systematic research to define the probabilities.

There is also a need for more research on the prevalence of criminal behaviour in sleep. It is usually preferable to have a parasomnia documented a priori than to seek to establish post-hoc evidence. This issue was identified by Mahowald and colleagues who reported an individual who experienced several incidents of violence allegedly in sleep, including chasing his wife and beating her with a hammer. Exhaustive investigations proved negative and it was felt he was trying to have his behaviour legitimated [2].

Psychiatric diagnoses that are often missed or not considered in the context of disorders of sleep (e.g., dissociation; fugue states) are also discussed and we emphasize an additional criterion for establishing the likelihood of a violent sleep disorder: physical proximity [3].

The first part of this review will focus on forensic sleep disorders, summarizing what is known and areas where evidence is lacking and the second part of this review will focus on the technical and legal aspects of violent parasomnias and behaviours arising out of sleep as examined under a common-law jurisdiction.