Shift Work Disorder: Clinical Assessment and Treatment Strategies
Richard D. Simon, Jr, MD
Listen to Audio Introduction
Identifying Circadian Rhythm Disturbances
The most important clue that a patient may have a circadian rhythm sleep disorder is an irregular sleep/wake schedule. It is not possible for people to change their circadian rhythm by more than 2–4 hours in any given day.1,2 Thus, if a person’s sleep/wake schedule varies by more than 2–4 hours between days on and off work, this suggests that he or she may have circadian rhythm problems. One of the best ways to identify such problems is to ask, “Do you have difficulty falling asleep at bedtime (insomnia) and difficulty waking up when you need or want to (hypersomnia)?” If the patient says yes, this can indicate a delayed sleep phase syndrome (ie, the person may be a “night owl”). Individuals with this sleep pattern often overuse the snooze button, hitting it repeatedly. This pattern is frequently seen in teenagers. People may also fall asleep very early, say at 8:00 PM (hypersomnia), and wake up long before they want to (eg, 3:00 AM). This sleep pattern reflects an advanced sleep phase syndrome, a pattern frequently seen in the elderly (AV 1).
Taking a Sleep History
The first step in assessing for shift work disorder (SWD) is to take a thorough sleep history. The most important item to ask about is the person’s schedule of work and sleep. Ask the person how his or her sleep/wake schedule differs on work days, days off, and vacation days. (The person’s sleep schedule when on vacation can give particularly helpful clues to the person’s intrinsic sleep/wake schedule.) (AV 2)
Assess the quality of sleep and wakefulness by asking questions such as these:
- Do you sleep all night? Do you feel refreshed in the morning? Or do you have fragmented sleep?
- Do you find it easy to stay alert throughout the day? Or do you find yourself getting fatigued and sleepy?
- Do you snore? Has anyone you live with witnessed any episodes when your breathing appeared to stop and then start again while you were asleep (sleep apnea)?
Restless legs syndrome, characterized by an uncomfortable, creeping, crawling, restless feeling in the legs, can make it very difficult to fall asleep. If the person reports snoring or witnessed episodes of apnea, abnormal nocturnal behaviors (eg, injuring self or others by acting out dreams), or symptoms suggesting narcolepsy, a sleep study is required. It is also important to ask about use of drugs or medications to help with sleep or alertness (eg, caffeine in the daytime, pills or alcohol to promote sleep) and the quality and safety of the sleeping and waking environments. A medical and psychiatric history is necessary to identify conditions that might be contributing to the sleep problems (eg, respiratory problems, pain, depression, anxiety).
The simplest and most important assessment tool for day-to-day clinical use by primary care physicians and general psychiatrists is a sleep diary (AV 3).
Several easy-to-use scales are also commonly used in sleep assessments. The Stanford Sleepiness Scale3 and the Epworth Sleepiness Scale4 measure level of excessive sleepiness. The Epworth Sleepiness Scale asks the person to rate the likelihood of dozing in 8 different situations on a 4-point scale (0 = would never doze to 3 = high chance of dozing), with a score of 10 or greater suggesting the need for further evaluation. The Insomnia Severity Index5 assesses severity of current sleep problems and their effect on daytime functioning. Scales such as these are particularly useful for tracking the effectiveness of an intervention over time.
In some situations, depression or anxiety scales or a general outcome scale such as the Short-Form 36-Item Health Survey, Version 2,6 may be useful.
Actigraphy, which uses a device worn on the wrist to record motion (ie, suggesting the person is awake) is not generally necessary in assessing for SWD, since an accurate history and a sleep diary will usually supply all necessary information. Referral for overnight sleep studies or polysomnography is also not indicated to diagnose SWD, but is indicated if one suspects the patient may have obstructive sleep apnea, parasomnias leading to injurious nocturnal behaviors during sleep, or narcolepsy. If narcolepsy is suspected in a shift worker, it is usually necessary to have the worker discontinue shift work for 2–4 weeks, because shift work itself and the associated circadian misalignment can confuse testing for narcolepsy. Narcolepsy is suggested by a history of excessive sleepiness that often started when the person was a teenager and predates his or her shift work.
Differential Diagnosis and Comorbid Conditions
Conditions that frequently occur in conjunction with SWD include obstructive sleep apnea and restless legs syndrome. Signs suggesting sleep apnea include large neck size, crowded oropharynx, and reports of witnessed apneas. Poor sleep habits of shift workers can also cause them to develop learned insomnia behaviors, referred to as psychophysiologic insomnia. Other comorbid conditions include depressive and/or anxiety disorders and chronic fatigue, which can be difficult to distinguish in a person with chronic circadian dyssynchrony.
The primary goal of treatment for SWD is to reduce the degree of circadian misalignment by fostering better sleep when it is desired and improved alertness and functioning when appropriate. Other goals are to identify and appropriately treat any intrinsic sleep disorders (eg, apnea) and any medical or psychiatric disorders that are present. Nonpharmacologic strategies should be tried before considering use of medications to promote sleep and/or alertness.
Zeitgebers: Strategies for Shifting the Biological Clock
The term zeitgeber (German for “time giver”) describes an external cue that helps synchronize a plant or animal’s internal clock to the earth’s 24-hour light/dark cycle.7 The most powerful zeitgebers in humans are light, supplemental melatonin, dark, and exercise.
Very bright light has powerful effects,1,2 with individuals being most sensitive to the effects of light approximately 2 hours before or 1–2 hours after their spontaneous wake time. If a pulse of very bright light is given 2–4 hours before a person’s spontaneous wake time (eg, 3:00 AM for someone with a usual wake time of 6:00 AM), the person is likely to wake up 2–4 hours later (ie, to move toward a delayed sleep phase, becoming more of a “night owl”). On the other hand, if you expose the person to very bright light at the spontaneous wake time or in the hour or so after, the person is likely to wake up 2–4 hours earlier (ie, to move toward an advanced sleep phase, becoming more of a “morning lark”).
Melatonin acts in the opposite way.1,2 When administered in the evening, it tends to make the person fall asleep and wake up earlier (ie, to advance the sleep phase). When administered in the morning, it tends to make the person stay up later and wake up later (ie, to delay the sleep phase).
Dark also has powerful effects on sleep phase.1,2 Thus, naps in a darkened environment act in much the same way as melatonin. Greatly limiting exposure to light in the evening will help you go to sleep earlier. Conversely, absence of light in the morning will help you sleep later. Because primarily the shorter wavelengths (eg, blue light) lead to phase shifts, one strategy for exposing the biological clock to dark is to wear dark or blue-blocking sunglasses.
Similar phase response curves have been found for exercise.1,2 Exercising in the early evening tends to phase-advance you and make you more of a morning person. Exercising after midnight generally does the opposite. However, exercise is not often used to adjust sleep phase in humans (AV 4).
Practical Strategies for Sleep Problems Associated With Shift Work
To minimize problems associated with shift work, workers should have as predictable a work schedule as possible. It is also helpful if employers provide sufficient breaks at work, allow shift workers to take a short nap at work, avoid schedules that involve working multiple days in a row, and provide sufficient time off between work days. These strategies are important because the vast majority of shift workers do not fully entrain (ie, their biological clocks never fully synchronize with their required work and sleep schedules). It is also useful to try to limit commuting time and overtime.
Another key strategy is to minimize circadian misalignment between work days and days off, which involves educating and enlisting the support of significant others in the shift worker’s family and immediate social circle. For most shift workers, this means producing a phase delay in their biological clocks (ie, to make them more “night owls”). This is done by changing the person’s environment so that he or she gets as much light as possible during the scheduled “day” and as little light as possible during the scheduled “night” and by minimizing the difference in sleep/wake patterns between work days and days off. Practically, this means having bright light at work, wearing dark glasses during the drive home when one is likely to be exposed to light, and keeping the bedroom, bathroom, and other rooms that will be used at home as dark as possible during the desired sleep period.
Shift workers who achieve complete or even partial entrainment (ie, their biological clocks become realigned with a new sleep/wake schedule) show marked improvements in psychomotor vigilance, memory, reaction time, night work performance, and mood and reductions in fatigue, excessive sleepiness, and mental exhaustion compared with those who do not8,9 (AV 5).
SWD needs to be considered in all patients who have a sleep/wake schedule that differs by more than 2–4 hours on work days compared with days off and who exhibit symptoms of sleepiness at work and difficulty sleeping during the desired sleep time. Asking about snoring and restless legs symptoms can lead to comorbid diagnoses that, if treated, can improve the shift worker’s sleep.
- Pandi-Perumal SR, Smits M, Spence W, et al. Dim Light Melatonin Onset (DLMO): a tool for the analysis of circadian phase in human sleep and chronobiological disorders. Prog Neuropsychopharmacol Biol Psychiatry. 2007;31(1):1–11. doi:10.1016/j.pnpbp.2006.06.020 PubMed
- Buxton OM, L’Hermite-Balériaux M, Turek FW, et al. Daytime naps in darkness phase shift the human circadian rhythms of melatonin and thyrotropin secretion. Am J Physiol Regul Integr Comp Physiol. 2000;278(2):R373–R382.PubMed
- Hoddes E, Zarcone V, Smythe H, et al. Quantification of sleepiness: a new approach. Psychophysiology. 1973;10(4):431–436. doi:10.1111/j.1469-8986.1973.tb00801.x PubMed. http://www.stanford.edu/~dement/sss.html. Accessed September 20, 2010.
- Johns MW. A new method for measuring daytime sleepiness: the Epworth Sleepiness Scale. Sleep. 1991;14(6):540–545. PubMed. http://www.stanford.edu/~dement/epworth.html. Accessed September 20, 2010.
- Morin CM, Espie CA. Insomnia: A Clinical Guide to Assessment and Treatment. New York, NY: Kluwer Academic/Plenum; 2003.
- Ware JE. User’s Manual for the SF-36v2 Health Survey –Second Edition. Lincoln, RI: QualityMetric Health Outcomes Solutions; 2007 (more information available at www.sf-36.org).
- Aschoff J. The phase-angle difference in circadian periodicity. In: Aschoff J, ed. Circadian Clocks. Amsterdam, Holland: North Holland Press; 1965:262–278.
- Crowley SJ, Lee C, Tseng CY, et al. Complete or partial circadian re-entrainment improves performance, alertness, and mood during night-shift work. Sleep. 2004;27(6):1077–1087. PubMed
- Smith MR, Fogg LF, Eastman CI. A compromise circadian phase position for permanent night work improves mood, fatigue, and performance. Sleep. 2009;32(11):1481–1489. PubMed