BASICS
DESCRIPTION
- The human system fundamentally relies on a natural circadian rhythm coordinated by the suprachiasmatic nucleus (SCN), an endogenous clock or pacemaker of the hypothalamus, which is responsible for linking the nervous system to the endocrine system (1).
- A shift in work schedule can desynchronize this circadian pacemaker with peripheral cells.
- The major environmental factor that can disrupt or reset the circadian rhythm is light at night (LAN) (1).
- Shift work disorder (SWD), also classified as circadian rhythm sleep disorder, shift work is a sleep disorder caused by a misalignment between the internal circadian rhythm and the required sleep-wake schedule resulting from erratic or nighttime shift work (2).
- Diagnostic criteria for SWD requires that all criteria for circadian rhythm disorders be met in addition to specific SWD criteria (see below).
- Criteria for circadian rhythm disorder:
- A persistent/recurrent sleep disruption due to either an alteration in the circadian (24-hour) timekeeping system or due to a misalignment between endogenous circadian rhythm and exogenous factors that affect sleep
- A complaint of insomnia/excessive daytime sleepiness or both
- An impairment in occupational, educational, or social functioning
- Insomnia or excessive sleepiness temporarily associated with a recurring work schedule that overlaps with the usual time for sleep
- Symptoms associated with shift work schedule are present for at least 1 month
- Sleep log or actigraphy monitoring (with sleep diaries) for at least 7 days demonstrates disturbed sleep (insomnia) and circadian and sleep time misalignment
- Sleep disturbance is not due to another current sleep disorder, substance use disorder, or medication use.
EPIDEMIOLOGY
Prevalence
- Shift workers include those who work night shifts, evening shifts, or rotating shifts, and comprise approximately 15 " 25% of the workforce in the United States (2).
- SWD has been estimated to affect 10 " 23% of the presently 22 million American shift workers, with a prevalence estimate of approximately 2 " 5% of the general population (14.1% night shift workers and 8.1% of rotating shift workers) (3).
PATHOPHYSIOLOGY
- Circadian rhythms are evident in multiple biologic functions, including body temperature, hormone levels, blood pressure, metabolism, cellular regeneration, sleep/wake cycles, and DNA transcription and translation (2).
- Transcription factors involved in circadian rhythm generation collectively referred to as the "molecular clock, " control production of the many proteins that are expressed within a period of approximately 24 hours. This molecular clock is self-sustaining but requires resetting daily or it may become out of sync with environmental cues also called "zeitgebers " (2).
- The most powerful zeitgeber, or timekeeper, is light. Light transmitted from the retinohypothalamic tract of the eye to the SCN of the hypothalamus upregulates the production of the "clock gene " (PER) (2).
- Periods of darkness cause the SCN to induce the release of melatonin from the pineal gland, which can also help to reset the molecular clock (2).
- A dysynchrony between the endogenous molecular clock and external cues (most notably light/dark cycles) is responsible for the development of circadian rhythm disorders and can have a severe impact on both physical and mental health (2).
RISK FACTORS
- Shift work, including night shifts, early morning shifts, or rotating shifts
- Younger age and "eveningness " (a.k.a. "night owls " rather than "morning larks " ) may provide some protection from the development of SWD (2).
Genetics
No genetic predisposition has been described.
GENERAL PREVENTION
- Limit rotating shifts.
- Use of bright light during shifts
- Scheduling brief, strategic 10- to 20-minute naps during shifts, if suitable
COMMONLY ASSOCIATED CONDITIONS
- Shift workers in general have impaired immediate free recall, decreased processing speed, and selective attention, impairments that may worsen with longer duration of shift work (2).
- Shift workers also have been shown to have a much higher risk of vehicular accidents, job-related injuries, absenteeism, and quality control errors (2).
- SWD has been associated with GI disease, specifically peptic ulcer disease, cardiovascular disease (CVD), infertility, mood disorders, and pregnancy complications (2).
- There is also evidence for possible increased risk of breast and prostate cancer. As such, the International Agency for Research on Cancer (IARC) has classified shift work that involves a circadian disruption as a probable carcinogen (1).
DIAGNOSIS
This is primarily a clinical diagnosis. However, there are some useful diagnostic aids.
HISTORY
- A careful history is critical to assess sleep disturbance including difficulty falling asleep, staying asleep, or nonrestorative sleep.
- Special attention should be paid to the following (4)[C]:
- Sleep/wake habits
- Degree of alertness or sleepiness
- Sleep environment
- Light exposure before, during, and after the shift
- Job-related factors: length of shift, number of consecutive shifts, commute after shift.
- Medications as well as over-the-counter (OTC) stimulants such as caffeine and energy drinks
- Impact on social and domestic responsibilities (including drowsy driving)
- It is also essential to evaluate for symptoms of other sleep disorders, which often coexist and can exacerbate SWD such as the following:
- Snoring (obstructive sleep apnea [OSA])
- Sudden sleep attacks and leg symptoms (restless legs syndrome [RLS])
- Falling asleep at inappropriate times, drop attacks, and daytime fatigue (narcolepsy)
PHYSICAL EXAM
Evaluate for depression, GI, CV, and potential cancer risk as well as signs of OSA such as obesity, a large neck, and a tight oropharynx (4)[C].
DIFFERENTIAL DIAGNOSIS
- Other primary sleep disorders: OSA, RLS, narcolepsy, and psychophysiologic insomnia.
- Other circadian rhythm sleep disorder such as delayed sleep phase disorder or jet lag syndrome. Distinguishing among these is challenging even for sleep specialists.
DIAGNOSTIC TESTS & INTERPRETATION
Given possible increased risk for CVD and cancer among shift workers, consider appropriate screenings.
Initial Tests (lab, imaging)
Fasting lipid panel, fasting glucose, age-appropriate cancer screenings
Diagnostic Procedures/Other
- Evaluation of a sleep/wake diary that records the patient 's sleep/wake habits including amount of sleep, naps during the waking hours, and mood (1 to 2 weeks) (4)[C].
- Consider actigraphy (a mechanical device, often worn on the arm/leg, to measure movement): serves as a gross measure of time and amount of activity and rest (4)[C]
- Polysomnography, a measure of sleep duration and quality is not typically used to diagnose SWD but may be helpful in ruling out other sleep/wake disorders such as sleep apnea and narcolepsy (2)[C].
- Several diagnostic tools are available including the Multiple Sleep Latency Test (MSLT), the Morningness-Eveningness Questionnaire (MEQ), and the Epworth Sleepiness Scale (ESS) to help determine circadian misalignment (2)[C].
Test Interpretation
Typically, sleep diaries and actigraph data reveal the following:
- Increased sleep latency
- Decreased total sleep time
- Frequent awakenings
- Notably, most people revert to nocturnal sleeping on their days off, meaning that every workweek, they start fresh in their attempt to shift their circadian rhythms to align with work schedules.
TREATMENT
- The only therapeutic modality deemed as "standard " by the American Academy of Sleep Medicine is planned (or prescribed) sleep schedules (5)[C].
- Other commonly used treatment strategies include optimizing sleep hygiene, bright light, melatonin, caffeine and other stimulants as well as hypnotics and other medication sleep aids (discussed below).
GENERAL MEASURES
- Sleep hygiene: An important first step in approaching the treatment of sleep disorders is to educate the patient on proper sleep hygiene including minimizing exposure to bright light before and during scheduled sleep periods (maintain a dark sleeping space, wear dark sunglasses following work shift, wearing eye mask to sleep), maintaining a quiet sleep environment (wearing ear plugs to sleep, disconnecting phone, doorbell), retraining core body temperature to shifted sleep/wake schedule (maintain cool sleeping quarters), and avoiding use of stimulants during second half of work shift (2)[C].
- Sleep time: Educate on need of protected time for sleep prior to and following work shifts with strategic use of naps when possible (4)[C].
- Address work/social/domestic factors: Treat psychosocial stress, depression, encourage healthy eating habits, limit substance use, increase exercise to at least 30 minutes 5 times per week (not within 2 to 4 hours of bedtime) (4)[C].
- Work-related interventions: If possible, reduce number of consecutive shifts (<4) or reduce shift duration (<12 hours), allow adequate time between shifts (>11 hours), and move heavy workload outside circadian nadir (04:00 to 07:00) (4)[C].
- Bright light: Several studies have demonstrated that timed bright light and darkness can promote adaptation to night work (6)[C].
- Bright light therapy with conventional light/light boxes (10,000 lux preferable, but >1,000 lux will help) should be given 30 min/day during the night/early morning shift prior to the nadir of the core body temperature rhythm (6)[C].
MEDICATION
- Melatonin may help shift circadian rhythms and can increase the quality and duration of sleep as well as increase alertness during the work shift.
- Ramelteon (Rozerem), a melatonin receptor agonist, is not FDA-approved for the treatment of SWD but may be helpful in improving daytime sleep (2)[C].
- Antidepressants: Doxepin (tricyclic) and trazodone are FDA-approved for the treatment of insomnia. Given at low doses, doxepin and trazodone can improve sleep without residual daytime impairment (2)[C].
- Intermediate-acting hypnotics zolpidem (Ambien) or eszopiclone (Lunesta) may be used (see below) but can cause postsleep sedation (2)[C].
- Wakefulness-promoting medications are as follows:
- Modafinil and armodafinil are FDA approved for excessive sleepiness in patients with SWD and can reduce daytime sleepiness and improve cognitive performance (2)[C].
- Prophylactic caffeine use (200 mg) immediately prior to work shift and during work shift (4)[C].
First Line
Circadian shift/sleep promoting: Melatonin, 3 mg PO or sublingual, 30 minutes before daytime sleep period. It should be taken only when the patient is home and able to go to bed if the hypnotic effects begin (2)[C].
Second Line
- Wakefulness-promoting:
- Modafinil (Provigil) 100 to 200 mg PO 60 minutes before the shift begins
- Armodafinil (Nuvigil) 150 to 250 mg is long-acting (12 to 16 hours, depending on food intake) and should be used judiciously in SWD as not to impede a patient 's ability to sleep after the shift.
- Sleep promoting:
- Non-benzodiazepine hypnotics
- Zolpidem (Ambien) 5 to 10 mg or eszopiclone (Lunesta) 2 to 3 mg 30 minutes before desired sleep period. Eszopiclone is the only hypnotic approved for use over 35 days.
- Antidepressants: Doxepin (1 to 6 mg) and trazodone (25 to 50 mg), 1 to 2 hours prior to bed (2)[C]
- Benzodiazepines: Estazolam, flurazepam, quazepam, temazepam, and triazolam are FDA-approved for the treatment of insomnia; however, they have high risk of tolerance and withdrawal, and should be used cautiously for short-term treatment of insomnia (2)[C].
- In general, hypnotics may improve daytime sleep; however, they do not appear to improve sleep maintenance, nighttime alertness, and may cause residual sedation during the work hours, potentially worsening SWD symptoms (2)[C].
ISSUES FOR REFERRAL
Refer to a sleep specialist if there is suspicion of other primary sleep disorders; dependence on hypnotics, alcohol, or stimulants
ONGOING CARE
PATIENT EDUCATION
- Health care providers should discuss good sleep hygiene and recommend on how to optimize the sleep environment.
- Shift workers who need to sleep in the daytime must take serious measures to ensure that their sleep environment is cool, dark, and quiet.
- Reserve bedroom for sleeping and intimacy only. Remove all televisions and telephones from bedroom.
- When going to sleep, turn clock away from bed; discourage prolonged reading in bed.
- Blackout shades are usually necessary in order to achieve the proper darkness.
REFERENCES
11 Stevens RG, Hansen J, Costa G, et al. Considerations of circadian impact for defining "shift work " in cancer studies: IARC Working Group Report. Occup Environ Med. 2011;68(2):154 " 162.22 Morrissette DA. Twisting the night away: a review of the neurobiology, genetics, diagnosis, and treatment of shift work disorder. CNS Spectr. 2013;18(Suppl 1):45 " 53.33 Roth T. Appropriate therapeutic selection for patients with shift work disorder. Sleep Med. 2012;13(4):335 " 341.44 Wright KPJr, Bogan RK, Wyatt JK. Shift work and the assessment and management of shift work disorder (SWD). Sleep Med Rev. 2013;17(1):41 " 54.55 American Academy of Sleep Medicine. The International Classification of Sleep Disorders: Diagnostic and Coding Manual. 2nd ed. Westchester, IL: American Academy of Sleep Medicine; 2005.66 Bjorvatn B, Pallesen S. A practical approach to circadian rhythm sleep disorders. Sleep Med Rev. 2009;13(1):47 " 60.
ADDITIONAL READING
- Morgenthaler TI, Lee-Chiong T, Alessi C, et al. Practice parameters for the clinical evaluation and treatment of circadian rhythm sleep disorders. An American Academy of Sleep Medicine report. Sleep. 2007;30(11):1445 " 1459.
- Sack RL, Auckley D, Auger RR, et al. Circadian rhythm sleep disorders: part I, basic principles, shift work and jet lag disorders. An American Academy of Sleep Medicine review. Sleep. 2007;30(11):1460 " 1483.
- Sleep Diary: http://www.helpguide.org/life/pdfs/sleep_diary.pdf.
CODES
ICD10
G47.26 Circadian rhythm sleep disorder, shift work type
ICD9
327.36 Circadian rhythm sleep disorder, shift work type
SNOMED
- 192000006 Work shift change (disorder)
- 3745000 sleep-wake schedule disorder (disorder)
CLINICAL PEARLS
- SWD is associated with shortened and disturbed sleep, fatigue, decreased alertness, cognitive decrements, increased injuries and accidents, reproductive problems, and risks to cardiovascular and gastrointestinal health, and has been classified as a carcinogen given possible association with breast and prostate cancer.
- The most important first diagnostic step in SWD is to obtain and evaluate a sleep diary.