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Recognition of shift-work disorder in primary care.

Practice recommendations

* To recognize shift-work disorder (SWD), primary care physicians can screen for persistent excessive sleepiness (ES) and insomnia in patients who work night or rotating shifts (SOR: B).

* If SWD is suspected, a differential diagnosis should be generated, as ES and insomnia are commonly associated with other morbidities. Ask patients about symptoms of other common sleep/wake disorders, such as obstructive sleep apnea and periodic limb movement disorder (SOR: B).

* The Epworth Sleepiness Scale is a useful tool for subjectively evaluating ES (SOR: A).

Shift-work disorder (SWD) is experienced by individuals whose work schedule overlaps with the normal sleep period, causing misalignment between the body's endogenous circadian clock and the time at which the worker is able to rest. The International Classification of Sleep Disorders, 2nd edition (ICSD-2) defines SWD as the presence of excessive sleepiness (ES) and/or insomnia for at least 1 month, in association with a shift-work schedule. (1)

This classification results in the shift-work population being separated into 3 distinct groups: those who have no impairment; those who have impairment but do not meet the ICSD-2 criteria for the diagnosis of SWD; and those who have SWD. Individuals in the last 2 groups are less likely to be able to meet the demands of shift work and, therefore, often return to non-shift-work schedules or retire from the workforce. This creates a "healthy worker effect," whereby workers remaining on night- or rotating-shift patterns are the best suited for this type of work. (2,3) However, retirement or changes to shift-work schedules are not an option for many workers, and patients with SWD must be recognized and treated in order to preserve their health and livelihood.

This article aims to characterize the symptoms and risk factors associated with SWD, with a view to assisting primary care physicians in the diagnosis and recognition of this consistently underrecognized sleep/wake disorder. (4)

Symptoms of SWD

Insomnia and ES (drowsiness and a propensity to sleep) are the defining symptoms of SWD and can result in fatigue (weariness and depleted energy), difficulty concentrating, reduced work performance, headache, irritability or depressed mood, and feeling unrefreshed after sleeping. (4,5) The consequences of insomnia and ES may, therefore, also be useful warning signs for SWD, and patients presenting with one or more of these sequelae should be evaluated for risk factors for SWD and asked about their symptoms using the differential diagnosis described below and in the FIGURE.

[FIGURE 1 OMITTED]

Risk factors for SWD

Vulnerability to SWD is dependent on certain predisposing and precipitating factors, including shift characteristics, circadian preference, job satisfaction, and susceptibility to sleep disturbance (see "The characterization and pathology of circadian rhythm sleep disorders" on page S12 of this supplement). The effects of some physiological and lifestyle factors, such as age and gender, on an individual's propensity to develop SWD have not been well quantified to date.

Shift type and pattern

Night-shift workers are reportedly most susceptible to SWD, with an estimated 32.1% of this group experiencing symptoms that meet the minimum diagnostic criteria for SWD compared with 26.1% of rotating-shift workers. (6) A recent study by Waage and others (7) found that 23.3% of oil rig swing-shift workers (2 weeks working 12-hour day/ night shifts followed by 4 weeks off) met ICSD-2 criteria for SWD. The relatively high prevalence of SWD in nightshift workers is thought to be due to exposure to light during rest periods and dark during the hours when the workers are attempting to be most productive. (6) Morning-shift workers are more susceptible to SWD than evening-shift workers, as delaying sleep appears to be more easily achieved than attempting to advance the rest period. (8)

The timing of shifts and changes to the shift schedule have been shown to significantly affect sleep, with individuals on rotating shifts experiencing the greatest detriments to their sleep quality. (8) In one study, workers on rotating shifts experienced significantly more difficulty sleeping than those on a stable shift schedule: 20.4% of rotating-shift workers reported a sleep latency >30 minutes vs 11.5% of fixed- or night-shift workers (P < .001). (8) Furthermore, while rotating-shift workers experienced a similar frequency of disrupted nights' sleep to that of other shift workers, they also reported a significantly higher number of night-time awakenings during each disrupted night's sleep (P < .05). In addition, approximately one-third of rotating-shift workers reported experiencing ES compared with 19% of night-or other shift workers and 12% of daytime workers (P < .001). Therefore, it is probably not surprising that rotating-shift workers were absent from work significantly more often than individuals on fixed day-shift schedules (62.8% vs 38.5%, respectively; P < .001) and had a significantly higher annual frequency of work-related accidents (19.5%) than those on fixed daytime (8.8%) or night-time shifts (9.6%) (P < .001). (8)

Advancing the rest period is reportedly more difficult than delaying sleep and is thought to be responsible for making counterclockwise shift rotation a risk factor for maladaptation to shift-work conditions. (9) Forward-rotating shift patterns have long been considered more beneficial to workers than backward-rotating patterns. (9) A rapidly forward-rotating shift system has been shown to have positive effects on sleep, to reduce ES, and to improve overall perceptions of general well-being compared with a slower backward-rotating shift pattern. (10) However, this study did not elucidate whether the new shift pattern reduced the negative effects of shift work to the level of those experienced by day workers.(10) The forward-rotating system was found to be particularly helpful to older workers, who experienced larger improvements in ES compared with younger workers. (10)

Shift timing in relation to"zeitgebers"

Bright light is the strongest "zeitgeber"--a cue responsible for the entrainment (synchronization) of the circadian clock. The body's natural circadian rhythms, and therefore the likelihood of developing ES and/or insomnia, will persist as long as shift workers continue to expose themselves to light at times that are inappropriate for re-entrainment (for example, exposure to light in the morning in night-shift workers). (11,12) One study found that workers who ensured that they slept in a darkened bedroom, wore dark glasses when commuting home, and avoided bright light on their days off were least affected by a night-shift schedule.(13) There is some evidence that shift workers respond to relative changes in light intensity over a 24-hour period rather than absolute light intensity, and bright light on the commute home in the morning from a night shift is enough to prevent re-entrainment of the circadian clock toward night working. (13) Interestingly, any degree of re-entrainment to the new rhythm is sufficient to confer significant benefits. Patients who either completely or partially re-entrained their circadian phase with respect to their night shift through the use of a fixed dark daytime sleep episode, sunglasses, melatonin, and bright light at night experienced substantial benefits in ES, performance, and mood (see "Managing the patient with shift-work disorder" on page S24 of this supplement).

Job satisfaction

Poor job satisfaction is associated with higher levels of ES in shift workers (14,15) and may therefore predispose an individual to SWD. Workers on rapidly rotating shifts who had poor job satisfaction did not have shorter sleep times but were sleepier at work compared with their satisfied colleagues (P < .001) and had poorer quality of sleep. (14) In a 3-year study, workers on a backward-rotating shift schedule who had poor job satisfaction had a higher likelihood of experiencing ES than individuals who were satisfied with their work (P = .026). (15) In addition, ES significantly increased in dissatisfied workers (P < .05) over the duration of the study compared with workers who were content with their jobs. (15)

Individual physiological and lifestyle factors

AGE. There is some disagreement in the literature as to the degree to which age affects adjustment to shift-work conditions, but the weight of current evidence suggests that advancing age is a risk factor for developing an intolerance to shift work. (2,3,16-19) Older individuals (ages 53-59 years) appear to adapt better initially to acute sleep deprivation than younger individuals (ages 19-29 years); however, older individuals show a reduced capacity for circadian adaptation when exposed to a series of night shifts. (17) Thus, although younger individuals are initially sleepier in response to a new shift pattern, they are capable of rapidly adapting to these changes. After 3 consecutive night shifts, younger workers were less sleepy than older workers (17); therefore, older workers are more likely to experience impairment while working night shifts even if they do not meet all of the ICSD-2 criteria for a diagnosis of SWD.

GENDER. Shift work may affect men and women differently. In a study of crane operators, women working night shifts or afternoon shifts slept approximately 30 minutes less than their male counterparts, (20) although this is unlikely to translate into an increased propensity to develop SWD in women. However, less sleep in female shift workers may reflect differences in the familial and/or social obligations of the male and female members of this worker population. The tendency for female shift workers to sleep less also emphasizes that extrinsic factors, such as childcare requirements, may have an impact on sleep during a shift-work schedule even in the absence of any innate circadian issues. (20) A more recent study found few gender-related differences in sleepiness and performance in workers on rapidly rotating shifts. (14) More detailed epidemiologic data are needed before any firm conclusions can be drawn on the influence of gender in SWD; currently it does not appear that gender is a risk factor for SWD.

CIRCADIAN PREFERENCE. It has been suggested that adults can be divided into "morning" or "evening" types (21) and the Morningness-Eveningness Questionnaire (MEQ) can be used to assess into which category an individual falls. (21) Morning-type individuals, or "larks," are most alert early in the day and are thought to be more susceptible to SWD, as they obtain less sleep (on average 86.8 minutes fewer) after a night shift than evening-type workers, or "night owls." (22) However, use of the MEQ is unproven in the evaluation of SWD. (23) Currently, there are no studies regarding whether there is a genetic component to SWD susceptibility (19); however, a number of reports have indicated that a preference for "morningness" or "eveningness" is genetically determined (see "The characterization and pathology of circadian rhythm sleep disorders" on page S12 of this supplement). In addition, an inherent vulnerability to insomnia or sensitivity to sleep loss may also lead to an innate susceptibility to SWD.

LIFESTYLE FACTORS. A number of lifestyle factors and choices can cause ES and insomnia in shift workers. These include the presence of other people in the home who may disrupt the attempted rest period; social obligations during the normal waking day that require the patient to be awake when he or she should be resting; patients attempting to sleep at "normal" times during days off and the weekend, thus lowering the chances of adapting to the shift-work pattern during the week; and deliberately staying awake or being unable to sleep during transitions between shift patterns, leading to sleep deprivation. These factors should be discussed with the patient at presentation, with a view to improving sleep hygiene. Such factors may trigger SWD in patients who are predisposed to developing this sleep/wake disorder; addressing poor sleep habits in patients who do not have SWD may help resolve their sleep problems.

Shift work can prevent individuals from enjoying a healthy lifestyle, with lower levels of physical exercise and higher levels of smoking seen in shift workers compared with non-shift workers. (15,24) Poor diet and lack of exercise as a result of social constraints or coping mechanisms associated with shift work may lead to metabolic imbalance, which can exacerbate symptoms of ES and insomnia. (24)

Habits adopted to cope with shift work may actually exacerbate the problems associated with night- or rotating-work schedules. For example, consumption of caffeinated drinks to enhance wakefulness or napping at inappropriate times may worsen insomnia when trying to rest. (25) Consumption of alcohol to induce sleep may increase ES during the next shifty Alcohol also interacts with certain shift characteristics to increase the risk of developing SWD and was found to be particularly detrimental to workers on a 3-shift rotation, with 51% vs 42% of regular alcohol consumers and nondrinkers experiencing insomnia, respectively. Although alcohol did exacerbate insomnia in the other shift workers studied, the effect was not as pronounced, with 48% of workers on a 2-shift rotation who consumed alcohol experiencing insomnia compared with 46% of their non-drinking counterparts. (24)

Differential diagnosis of SWD in the primary care setting

The American Academy of Sleep Medicine notes that the boundary between a "normal" response and a pathologic response to shift work is not clearly defined and that the validity and reproducibility of diagnostic criteria need testing. (19) To add to the challenges inherent in defining SWD, ES, insomnia, and a number of their sequelae (see "Symptoms of SWD" on page S18 of this article) are also indicative of a variety of disorders other than SWD. For example, ES and/or insomnia are also symptoms of other sleep/wake disorders, sleep deprivation, pre-existing medical conditions (including mood disorders and central nervous system issues such as narcolepsy and brain injury), the use of sedative or stimulant medications, and substance abuse. The discussion of a patient's full medical history should assist in ruling out other potential causes for his or her symptoms, but it is also vital to generate a differential diagnosis to exclude the other potentially causative conditions. (Examples of how mood disorders and other sleep/wake disorders can be differentiated from SWD appear below.)

Mood disorders and sleep/wake disorders often present in the primary care setting and can at first seem indistinguishable. For example, patients with ES as a result of a sleep/wake disorder may superficially appear to have depression, as a lack of energy, poor memory, reduced concentration, and a loss of interest in life are common features of both ES and mood disorders. In such instances, asking the patient about his or her sleep habits and the use of simple depression questionnaires such as the Patient Health Questionnaire-9 (www.patient.co.uk/showdoc/40025272/) are vital to avoid misdiagnosis and prescription of inappropriate medication.

ES is also a symptom of the sleep/wake disorders obstructive sleep apnea (OSA) and restless legs syndrome (RLS), which are commonly reported in shift workers. (26,27) Patients with OSA have poor quality sleep, as they experience repeated full or partial blockages of their airway, resulting in snoring and episodes of choking or gasping during sleep. (28) Recurrent partial or complete obstruction of the upper airway leads to repeated arousals and disturbed sleep, which can cause ES. (29,30) Night-shift work has been shown to aggravate OSA, (31) possibly due to the increased potential for weight gain and metabolic disturbance in this population (24); overweight and metabolic syndrome are risk factors for and comorbidities associated with OSA. (28) It is imperative that patients with suspected OSA are referred to a sleep specialist as well as counseled about appropriate therapies and lifestyle changes. (32)

RLS may develop in shift workers due to low serum iron levels induced by chronic sleep deprivation. (33) Patients with symptoms of RLS should have their serum ferritin levels checked and, if found to be <50 mcg/mL, a trial of oral iron therapy may be of benefit. (34) If serum ferritin is normal or symptoms of RLS persist, patients can be treated with a dopamine agonist such as pramipexole or ropinirole. (34) If therapy with a dopamine agonist is not successful, the patient should be referred to a sleep specialist for further treatment and given guidance regarding sleep hygiene. The FIGURE provides a suggested set of questions that could form the basis of a differential diagnosis of sleep/wake disorders in shift-working individuals presenting with symptoms of ES and/or insomnia.

Further assessment of patients with suspected SWD

Further assessment for SWD is advised if the patient works shifts, has been experiencing symptoms of ES and insomnia for [greater than or equal to] 1 month, and does not have the signs and symptoms of other sleep/wake disorders. Recent practice parameters from the American Academy of Sleep Medicine recommend the use of a sleep diary for [greater than or equal to] 7 days to aid in the diagnosis of SWD and to rule out other sleep/wake disorders. (19, 23) At present, there are no standard sleep diaries, and many clinicians create their own so that patients can capture data on the quantity and quality of their sleep.

The Epworth Sleepiness Scale (ESS) is helpful in measuring ES in the primary care setting. (35) This brief questionnaire, which can take as little as 2 minutes to complete, asks the patient about his or her chances of dozing in 8 sedentary situations, such as when reading a book or sitting in a meeting. A score of [greater than or equal to] 10 out of a possible 24 is indicative of clinically significant ES. (35) However, as the situations described in the ESS are more oriented toward activities of day to day living, they may not be completely appropriate for the measurement of ES in a shift-work situation. Furthermore, the ESS is not validated in night-or rotating-shift workers. Nonetheless, the ESS is useful both as a screen for ES and for follow-up of therapy.

Because the diagnosis of SWD is based on patient history, it does not require confirmation with a sleep study. However, if the patient has symptoms suggestive of OSA or another sleep/wake disorder, then further evaluation, including a sleep study or polysomnogram, is warranted.

Summary

The difference between a "normal" and a pathologic response to shift work is not clearly defined. As a result of this uncertainty, SWD is underrecognized, underdiagnosed, and underrepresented in published clinical studies. The main symptoms of SWD--ES and insomnia--are also characteristic of a number of other conditions, including a variety of sleep/wake disorders. For this reason, exclusion of other potential causes of ES and insomnia is necessary before a firm diagnosis of SWD can be given. Further research is required to establish the physiologic basis of individuals' vulnerability to SWD. Such studies would be helpful in identifying risk factors for SWD and delineating normal and pathologic responses to shift-work conditions.

References

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(34.) Silber MH, Ehrenberg BL, Allen RP, et al. An algorithm for the management of restless legs syndrome. Mayo Clin Proc. 2004;79:916-922.

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Jonathan R. L. Schwartz, MD

University of Oklahoma Health Sciences Center

INTEGRIS Sleep Disorders Center of Oklahoma

Oklahoma City, Oklahoma

Dr Schwartz reports that he serves as a consultant to and on the speakers bureaus of AstraZeneca, Boehringer Ingelheim Pharmaceuticals, Inc., Cephalon, Inc., Pfizer Inc, Sepracor Inc., Takeda Pharmaceuticals North America, Inc, and GlaxoSmithKline.
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Author:Schwartz, Jonathan R.L.
Publication:Journal of Family Practice
Geographic Code:1USA
Date:Jan 1, 2010
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