SHIFT WORK DISORDER - myCME.com

Shift Work Disorder and Jet Lag Zee and Goldstein 397IntroductionHumans have an endogenous circadian rhythmslightly longer than 24 h. The International Classificationof Sleep Disorders describes nine circadianrhythm disorders defined by a persistent or recurrentpattern of sleep disturbance resulting from eitheralterations of the circadian timekeeping system ormisalignment between the endogenous circadianrhythm and exogenous factors that affect the timingand duration of sleep [1]. Shift work disorder andjet lag are two circadian rhythm disorders that occurdue to the alteration of the external environmentrelative to the internal circadian timing system[2].Shift work disorderAs of 1991, 20% of the United States workforce participatedin some type of shift work [3]. Of these, morethan 30% of night workers and 25% of rotating shiftworkers meet criteria for shift work sleep disorder[3]. In Europe, only 24% of the workforce keeps conventionalworking hours, and 18.8% have a workschedule that involves night shift work [4]. Shift workdisorder is characterized by both insomnia and excessivesleepiness associated with the work period occurringduring the usual time for sleep [1]. The diagnosisrequires that symptoms are of at least 1 month’s durationand circadian misalignment must be demonstratedwith a sleep diary or actigraphy [1]. Insomnia andexcessive sleepiness are thought to be primarily dueto a misalignment between the scheduled sleep/wakecycle and the circadian propensity for sleep and alertness.Typically, the patient is attempting to sleep whenthe circadian signal for alertness is high and working ata time when the circadian alertness levels are low [1].In addition to circadian factors, sleep is often shortenedin shift workers because of problems with the environmentfor sleep and because domestic and socialresponsibilities encroach on the worker’s nonconventionalsleep time [2]. Therefore, sleep loss, in additionto circadian misalignment, contributes to decreasedalertness during night work [5]. Sleepiness in shiftworkers can be profound: one third of night workersadmit to nodding off once a week during work, andone half report falling asleep while commuting [6].In addition to sleepiness, circadian misalignments inperformance have also contributed to serious accidents,including the incidents at Three Mile Islandand Chernobyl and the Exxon Valdez disaster [5]. Shiftworkers with shift work disorder are at higher risk forcardiovascular disease, ulcers, depression, and absenteeismthan shift workers without shift work disorder[5]. Because of both public safety concerns and consequencesto the patient, treatment of shift work disorderis imperative.Jet lag disorderJet lag disorder is defined as symptoms of insomniaand/or excessive daytime sleepiness resulting fromtravel across at least two time zones [1]. It is also associatedwith compromised daytime function, generalmalaise, or somatic complaints (eg, gastrointestinalsymptoms) occurring within 1 to 2 days of travel [1].Unlike travel fatigue, jet lag symptoms do not resolvewith an adequate sleep period upon arrival and mayoccur even when unfavorable air travel conditions(cramped space, etc.) are minimized [7]. Because theintrinsic clock cannot adjust to the change in timezones as rapidly as we can traverse them with jet travel,there is a resultant discord between the timing of sleepas generated by the endogenous circadian rhythm andthe sleep/wake times necessary in the new time zone[8••]. Eastward travel often results in sleep-onset insomniaas the endogenous circadian rhythm (as setby the location of origin) is not conducive to sleepat the new, earlier time at the destination; the circadianrhythm must advance. In westward travel, difficultiesin remaining asleep are a more prominentproblem, as the circadian alerting signal occurs duringthe desired sleep period at the new destination; the circadianrhythm must delay [7]. In either case, sleepinessresults from both circadian misalignment andtruncated sleep duration. In jet travel, it has beendemonstrated that the endogenous circadian rhythmresets approximately 92 min later each day after aflight westward and approximately 57 min earliereach day after a flight eastward. Therefore it is moredifficult to align the intrinsic rhythm with the externalclock in eastward travel [9]. Alignment may occur inthe opposite direction (referred to as antidromic reentrainment)when traveling across more than eighttime zones [10]. In addition to the direction of travel