Sleep dysfunction in PD is multifactorial, and as many as 98% of patients with PD may suffer at some time from nocturnal symptoms that can disturb their sleep (2). Overall prevalence figures range from 25% to 98% (2-4). A community-based study reported 60% of PD patients with sleep problems, compared with 33% of age- and sex-matched healthy controls (4). The NMSQuest study in 123 PD patients across all age groups and 96 age-matched controls, using a validated nonmotor symptom questionnaire in an international multicenter setting, identified high rates for a range of sleep-related disorders (14). Although some complaints such as nocturia (67%) were common in controls, other complaints such as insomnia (41%), intense/vivid dreams (31%), acting out during dreams (33%), restless legs (37%), and daytime sleepiness (28%) were more prevalent in PD and may reflect more fundamental dysfunction of sleep-related mechanisms. In another observational study, Hely et al. (15) evaluated PD patients for a period of 15 to 18 years after being recruited to a
TABLE 1 Causes of Nighttime Sleep Disruption and Daytime Sleepiness in Parkinson's Disease Patients
Urinary difficulties Neuropsychiatric/parasomnias
Fragmentation of sleep (sleep maintenance insomnia)
Akinesia (difficulty in turning)
Periodic limb movements of sleep
Sensory problems (pain, paresthesia)
Nocturia with secondary postural hypotension
REM behavior disorder
Nocturnal off-period-related tremor
Off-period-related pain/paresthesia/muscle cramps Off-period-related incontinence Hallucinations Vivid dreaming
? Off-period-related panic attacks ? REM behavior disorder Akathisia
Alerting effect, nocturnal agitation
Abbreviation: REM, rapid eye movement;?, possible clinical phenomenon. Source: From Ref. 6.
bromocriptine versus levodopa trial. One-third of the original cohort was evaluated, and most had significant nonmotor symptoms including sleep disorders, which were more troublesome and disabling than the motor symptoms or levodopa-induced dyskinesia. A study by Shulman et al. (16) reported that nonmotor symptoms of PD are frequently overlooked, even in movement disorder centers.
Sleep disturbances of PD may be grouped into four broad categories: insomnia, motor, urinary, and neuropsychiatric (Table 1). Daytime somnolence or excessive daytime sleepiness (EDS) is also an important issue. Sleep architecture studies in PD show variable results but, on the whole, common features are reduced total sleep time and sleep efficiency, multiple sleep arousals, and fragmentation of sleep (7,8,17,18). A circadian variation of symptoms has been identified and, as such, patients can be classified into a "morning better," "morning worse", and a nonaffected group (7). EDS is an important aspect of sleep-related morbidity of PD and may be caused by the underlying dopaminergic denervation, dopaminergic medications, or may be due to poor nocturnal sleep (17). In the following section, we will review some key aspects of the pathophysiology of sleep dysfunction in PD and related sleep disorders.
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