Parkinson’s Disease (PD) is a progressive neurodegenerative disorder recognized primarily by its motor symptoms, such as tremor, rigidity, and slowed movement. However, the disease also affects numerous non-motor functions, often causing significant changes in daily life. Among these non-motor symptoms, sleep disturbances are extremely common and can manifest as difficulty sleeping at night or, conversely, an overwhelming urge to sleep during the day. Therefore, experiencing excessive sleepiness is a frequent, though often challenging, reality for many individuals living with PD.
Excessive Daytime Sleepiness is Common
The symptom of excessive daytime sleepiness (EDS) affects a large portion of the PD population, with studies showing a pooled prevalence of around 33% to 35% across various cohorts. In some clinical settings, the reported rates can be higher, reaching 50% or more, indicating this is a widespread concern. EDS is defined by an irrepressible need for sleep or inappropriate lapses into drowsiness. This is not simply feeling tired, but a profound inability to maintain wakefulness, often leading to involuntary sleep episodes.
The severity of daytime sleepiness tends to increase as the disease progresses and with longer disease duration. This symptom significantly compromises safety, particularly regarding activities like driving, and diminishes overall quality of life.
Intrinsic Disease Mechanisms Causing Sleepiness
The neurodegeneration in PD affects brain regions that regulate the sleep-wake cycle. The disease process causes damage to specific wake-promoting neuronal systems. A primary mechanism involves the loss of orexin-producing neurons located in the hypothalamus.
Orexin is a neuropeptide that regulates wakefulness and arousal. The loss of these neurons directly impairs the brain’s ability to maintain alertness, mimicking symptoms of narcolepsy. This damage contributes to EDS independently of medication effects.
Nighttime sleep quality is often fragmented due to the disease, including motor symptoms and REM Sleep Behavior Disorder (RBD). Poor quality sleep overnight compounds this neurological deficit, resulting in greater daytime sleepiness.
Medication Side Effects That Induce Sleepiness
Medications used to manage the motor symptoms of PD frequently contribute to excessive daytime sleepiness. Dopamine Agonists (DAs) are particularly notorious for causing this side effect. These drugs stimulate dopamine receptors, which can extend to sleep regulation centers, leading to sudden, irresistible sleep episodes called “sleep attacks.”
Sleep attacks can occur with little warning. While DAs are the most commonly implicated, this is considered a class effect. Other dopaminergic medications, including Levodopa, can also contribute to somnolence, especially when taken at higher doses or in combination with other sedating drugs.
Managing Excessive Sleepiness
Managing EDS begins with a review of current medications. Adjusting or discontinuing sedating drugs, particularly Dopamine Agonists, is often the first step. Any medication contributing to sleepiness should be reviewed by the neurologist.
Optimizing nighttime sleep is a primary focus, requiring attention to sleep hygiene, such as maintaining a proper sleep environment. Consistent sleep and wake times are helpful, as is treating nocturnal motor symptoms like tremor or urinary frequency that disrupt sleep continuity. Short naps can be incorporated into the daytime routine to mitigate sleepiness, but excessive or prolonged napping should be avoided.
Pharmacological interventions may be considered if behavioral adjustments are insufficient. Wake-promoting agents, such as modafinil or armodafinil, can be prescribed to improve alertness. These medications should only be used under medical supervision with careful dose titration.