Shift Work Sleep Disorder

What is shift work sleep disorder (SWSD)?
SWSD is classified as one of the circadian rhythm disorders (CRDs) and occurs in people who work shifts (particularly night shifts). It is caused by continued change to the person's sleep-wake schedule. Most people demonstrate a remarkable ability to adjust to this repeated mismatching; however, individuals who experience persistent, severe symptoms are diagnosed as having SWSD. SWSD is characterised by disrupted or shortened duration of sleep and an inability to remain alert when required. Consequently, one of the main symptoms is Excessive Sleepiness (ES), and this adversely affects the person's ability to perform the work required.

What are the symptoms of SWSD?
All patients with a CRD may complain of insomnia at certain times when they should be asleep, and ES at other times. This disrupted sleep-wake pattern can impair the patient's functioning at work and in social situations. As a consequence, CRDs can cause the person distress. SWSD is no different: falling asleep at work or whilst driving can be extremely distressing, as well as potentially dangerous, and it may be this event that provokes the person to consult their doctor.

Sleep disruption in patients with SWSD is shown by shorter sleep duration and more frequent disturbances in sleep. In other words, patients will often have less sleep and what sleep they do get is less restorative or refreshing. In particular, when studied during their normal sleep hours, many patients with SWSD show a reduction in certain stages of sleep. The Multiple Sleep Latency Test (MSLT), a test used to evaluate a patient's sleepiness, shows a high degree of sleepiness during times when the patients are required to remain awake. This sleepiness is undoubtedly caused by the demands imposed by shift work: when studied following a period of adjustment to a normal sleep-wake schedule, these same individuals were shown to have normal night-time sleep and normal levels of daytime sleepiness and alertness.

No matter how long the patient has been working shifts, the 24 hour body timing system never completely adjusts to night work. Most night workers sleep during their nights off and workers who do this must adapt to a large shift in their sleep-wake schedule every week.

What is the impact of SWSD at work?
Sleep loss and disrupted sleep can lead to reduced performance, including increased variability in performance, slowed physical and mental reaction time, increased errors, decreased awareness, impaired memory and reduced motivation.

One of the inevitable consequences of SWSD is a person’s potential increase in industrial or other work-related accidents. Night-shift workers (in general) already have reduced night-time alertness and performance and an increased accident rate compared with those on a day shift. Industrial accidents occurring at night are common, with infamous examples being those at Chernobyl, Three Mile Island and Bhopal. An individual with SWSD would be even more at risk of a work related accident or of an accident while driving.

What is the impact of SWSD on social and family life?
Dysfunction in occupational, family, and social roles is often observed in people who have difficulty coping with shift work and this may be the case for patients diagnosed with SWSD. Patients may also be irritable owing to the lack of sleep or to the conflict between the demands for sleep and the demands for social activities. Time that would otherwise be spent with friends and engaging in social activities is often spent sleeping and adjusting to the next shift.

What causes SWSD?
SWSD is caused by continued change to the person's sleep-wake schedule. Most people demonstrate a remarkable ability to adjust to this repeated mismatching; however, individuals who experience persistent, severe symptoms are diagnosed as having SWSD.

How is SWSD diagnosed?
SWSD is usually diagnosed by means of an interview and a sleep study may also be useful. During the interview, the doctor will review the patient's sleep behaviours and experiences. This is known as the patient's 'sleep history'. A patient will usually consult their GP following an episode of ES, possibly during which he or she fell asleep at work or when driving.

The severity of SWSD can be evaluated using a sleep study. Ideally, the sleep study should be performed during the 'shifted' sleep period and the individual should be monitored in the work environment. A 24-hour recording over the first and last of the series of rotating shifts should be performed. In addition, the patient should be monitored during usual daytime wakefulness for a comparison.

How is SWSD treated
The best treatment for SWSD is a reduction in the number of changes to the patient's sleep-wake pattern. Patients are advised to negotiate changes in their shift or working patterns or even completely stop working shifts. Alternatively, SWSD patients may benefit from regularly scheduled naps during the day before the shift. Some patients may even be able to take naps during the shift. What sleep the patient is able to get should be of good quality and in order to ensure this, advice concerning sleep hygiene is often given.

Excessive sleepiness in SWSD
As described previously, ES is the primary symptom of SWSD and this impairs patients' performance at work, restricts or damages family and social lives, and damages general health. Owing to the need to perform at work and work in shifts, it is often not possible to implement simple solutions such as alteration of imposed sleep-wake schedules or nap taking.

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