Parkinson’s Disease (PD) is a progressive neurological disorder primarily known for its impact on motor function, including the characteristic rhythmic shaking known as a resting tremor. This tremor occurs when the affected limb is at rest and typically resolves when the person initiates a voluntary movement. The characteristic resting tremor of PD generally ceases or is significantly suppressed when a person is in a state of deep sleep. While the tremor disappears, PD patients often experience other disruptive nocturnal movements, leading to a common misconception that they are “shaking” in their sleep.
The Nature of Parkinsonian Tremor During Sleep
The resting tremor experienced during wakefulness is a hallmark of PD, often described as a “pill-rolling” motion in the hands. This involuntary movement is a result of the loss of dopamine-producing neurons in the substantia nigra region of the brain.
The suppression of this tremor during sleep is a physiological phenomenon linked to the brain’s natural regulation of motor control during different sleep stages. During Non-Rapid Eye Movement (NREM) sleep, the waking tremor is transformed into subclinical muscle contractions that decrease in amplitude as sleep deepens. While a small amount of muscle activity may be detectable, it is typically not noticeable to the patient or a bed partner.
When the brain enters Rapid Eye Movement (REM) sleep, the tremor essentially disappears. REM sleep is normally characterized by muscle atonia, a temporary paralysis mediated by signals from the brainstem that prevent the body from acting out dreams. The brain’s motor control loop appears temporarily re-established, inhibiting the parkinsonian tremor. The tremor may, however, persist or even intensify during the transition period just before falling asleep or immediately upon waking.
Primary Sleep Disorders and Nocturnal Movements in Parkinson’s Disease
While the resting tremor is largely absent during deep sleep, PD is highly associated with several sleep disorders that cause significant, noticeable movement at night. These nocturnal movements are often mistaken for the resting tremor.
One of the most common and disruptive issues is REM Sleep Behavior Disorder (RBD), which can affect up to 70% of people with PD. RBD occurs when the muscle atonia that should naturally happen during REM sleep is lost due to neurodegeneration in the brainstem. This failure of muscle paralysis allows the person to physically act out vivid dreams by shouting, punching, kicking, or thrashing. RBD movements are rapid, coordinated, and purposeful, unlike the rhythmic resting tremor, and can lead to injury for the patient or their bed partner.
Another source of disruptive movement is nocturnal akinesia, which is a form of “off” period where the effects of daytime dopaminergic medication wear off overnight. This hypodopaminergic state leads to rigidity, stiffness, and extreme difficulty changing position or turning over in bed. Up to 65% of PD patients report difficulty turning over, which can cause frequent awakenings and pain. This reduced mobility can also lead to painful cramping, known as dystonia, often in the feet or legs, which is a sustained muscle contraction.
Restless Legs Syndrome (RLS) is also more prevalent in people with PD, affecting approximately 14% of PD patients. RLS is characterized by an irresistible urge to move the legs, usually accompanied by uncomfortable sensations that begin or worsen during periods of rest or inactivity. The need to move the legs to relieve these sensations causes disruptive leg movements, which are distinct from the PD resting tremor.
The Vicious Cycle: Sleep Quality and Daytime Symptoms
The cumulative effect of these nocturnal disturbances is severely fragmented and non-restorative sleep. Up to 80% of PD patients experience frequent awakenings, often spending 30% to 40% of the night awake. This lack of restful sleep establishes a negative cycle that significantly worsens motor and non-motor symptoms during the day.
Poor sleep quality directly exacerbates daytime fatigue and excessive daytime sleepiness, which affects 30% to 50% of PD patients. This sleep deprivation also intensifies motor symptoms like bradykinesia (slowness of movement) and rigidity, and contributes to cognitive issues like poor concentration and “cognitive fog”.
Addressing these sleep issues often involves consulting a neurologist or sleep specialist to identify the specific cause, which may require a formal sleep study. Management strategies can include optimizing the timing of dopaminergic medications, such as using an extended-release formula at bedtime to manage nocturnal akinesia and rigidity. Non-pharmacological approaches, such as improving sleep hygiene by establishing a set sleep schedule and avoiding sedentary activities, are recommended to support better sleep architecture. For RBD, a safe sleeping environment and medications like melatonin or clonazepam are often used to reduce dream enactment behaviors.