Fatigue correlates with sleep disturbances in Parkinson disease

For the 10 million people worldwide living with Parkinson’s disease (PD), fatigue isn’t just tiredness—it’s a daily battle that can overshadow even motor symptoms like tremors or stiffness. Over half of PD patients rank fatigue among their top three most disabling challenges, yet it’s often overlooked by doctors because classic PD rating scales (like the Unified Parkinson’s Disease Rating Scale, UPDRS) don’t measure it. But new research suggests the sleep problems many PD patients face—from trouble staying asleep to acting out dreams—could be making that fatigue worse.

A 2021 study by researchers from Soochow University and Johns Hopkins University, published in the Chinese Medical Journal, used overnight sleep studies (polysomnography, or PSG) to uncover a clear link between sleep disturbances and fatigue in PD. It’s one of the first studies to use objective sleep data—rather than self-reported surveys—to explore this connection.

Why Fatigue and Sleep Matter in Parkinson’s

Fatigue in PD is unique: it’s a persistent, overwhelming exhaustion that doesn’t go away with rest. Studies estimate it affects 33% to 58% of PD patients, depending on how it’s measured. Sleep problems are even more common—up to 98% of PD patients struggle with issues like insomnia, restless legs syndrome, or REM sleep behavior disorder (RBD), a condition where people act out their dreams (e.g., shouting, flailing, or getting out of bed) because their muscles don’t relax during REM sleep (the dreaming stage).

Logically, poor sleep should worsen fatigue—but prior studies lacked the tools to prove it. This new research filled that gap by using PSG, a gold-standard test that tracks brain waves, eye movements, muscle activity, and breathing during sleep.

How We Studied the Link

The team recruited 232 PD patients from a hospital in Suzhou, China, between 2014 and 2018. They split participants into two groups using the Fatigue Severity Scale (FSS):

Mild fatigue: FSS score <4 (152 patients)
Severe fatigue: FSS score ≥4 (80 patients)

All patients underwent overnight PSG to measure:

Sleep stages (e.g., REM vs. non-REM sleep)
REM sleep behavior disorder (RBD)
Muscle activity during REM sleep (called “REM sleep without atonia,” or RWA)
Sleep efficiency (how much time spent asleep vs. in bed)

The researchers also collected data on:

Motor symptoms (UPDRS, Hoehn and Yahr stage)
Depression (Hamilton Rating Scale for Depression)
Anxiety (Hamilton Anxiety Rating Scale)
Daytime sleepiness (Epworth Sleepiness Scale)
Medication doses (levodopa equivalent daily dose, or LEDD)

Patients with severe anxiety, atypical Parkinsonism, or medications that affect sleep (e.g., antidepressants, beta-blockers) were excluded to ensure results were reliable.

What We Found

The results were clear: severe fatigue was strongly linked to both worse clinical outcomes and more disrupted sleep.

Clinical Correlates of Severe Fatigue

Patients with severe fatigue had:

Longer disease duration (5.4 years vs. 3.2 years for mild fatigue)
Worse motor symptoms (higher UPDRS scores)
Higher levodopa doses (more medication to manage symptoms)
More depression and anxiety
More non-motor symptoms like excessive salivation and urinary urgency

These findings align with prior research showing fatigue in PD is often tied to a heavier burden of motor and emotional symptoms.

Sleep Correlates of Severe Fatigue

The most striking results came from the PSG data:

Less REM sleep: Patients with severe fatigue spent just 13% of their sleep in REM (the stage where the brain restores itself) compared to 16% for those with mild fatigue. Less REM sleep is linked to poorer cognitive function and energy levels in healthy people—and this study suggests it’s a key driver of fatigue in PD.
More RBD: 67% of severe fatigue patients had RBD (confirmed by PSG) vs. 51% of mild fatigue patients. They were also 2.3 times more likely to have RBD overall. RBD is a known early sign of PD, but this study is the first to link it directly to fatigue.
Higher muscle activity during REM: Patients with severe fatigue had more “REM sleep without atonia (RWA)” — meaning their chin muscles stayed tense during REM (normal REM sleep should have relaxed muscles). This is a hallmark of RBD and may explain why patients feel exhausted: tense muscles during sleep mean the body doesn’t rest.

Importantly, all these links remained statistically significant even after adjusting for age, sex, disease severity, and other sleep problems like sleep apnea.

What This Means for PD Patients

The study’s findings have two big takeaways:

1. Fatigue in PD isn’t “just tiredness”—it’s a subtype linked to sleep and biology

The authors suggest fatigue could be a “special subtype” of PD because it’s tied to specific sleep changes (less REM, more RBD) and biological markers. Prior research has linked both fatigue and RBD to α-synuclein oligomers—toxic protein clumps found in the brains of PD patients—in cerebrospinal fluid (CSF). These oligomers are the most harmful form of α-synuclein (the protein that builds up in Lewy bodies, a hallmark of PD) and may be released from dying neurons. Higher levels of these oligomers are linked to faster disease progression—meaning fatigue and RBD could be early signs of more aggressive PD.

2. Sleep problems drive fatigue (and vice versa)

The study supports a “feedback loop” between fatigue, sleep, and PD symptoms:

Poor sleep (e.g., RBD, less REM) worsens fatigue.
Fatigue increases stress and depression, which further disrupt sleep.
Both fatigue and sleep problems worsen motor symptoms (like bradykinesia, or slow movement), making daily life harder.

Breaking this cycle could be key to improving quality of life for PD patients. For example, treating RBD (with medications like clonazepam or melatonin) might reduce fatigue, and managing fatigue (with exercise or cognitive behavioral therapy) could improve sleep.

Limitations to Consider

Like all research, this study has limits:

Small, single-center sample: The 232 patients were from one hospital in China, so results may not apply to all PD patients (e.g., those with severe disease or different genetic backgrounds).
Self-reported fatigue: The FSS is a useful tool, but it relies on patients’ subjective experiences. Future studies could use more objective measures (e.g., activity trackers) to confirm fatigue levels.
Mild-to-moderate PD: Most patients were in the early to middle stages of PD. Results may not extend to those with severe disease, who often have more complex sleep problems.

Final Thoughts

For PD patients and caregivers, this study is a wake-up call: fatigue isn’t a “minor” symptom—it’s a critical part of the disease linked to sleep and biology. If you or a loved one has PD and struggles with fatigue, ask your doctor about:

A polysomnography (PSG) to check for RBD or other sleep issues
Screening for depression and anxiety (which worsen both fatigue and sleep)
Adjusting medications (e.g., levodopa doses) to reduce fatigue

For researchers, the study highlights the need to prioritize fatigue in PD research. Fatigue is one of the most disabling symptoms for patients, but it’s often ignored in clinical trials. More studies on treatments (e.g., sleep therapy, medications targeting α-synuclein) could help millions of PD patients regain their energy.

As the study’s authors conclude: “Fatigue is an easily neglected symptom, but our work shows it’s linked to critical changes in sleep. More research should focus on this debilitating issue to improve outcomes for PD patients.”

References

Friedman JH, Brown RG, Comella C, et al. Fatigue in Parkinson’s disease: a review. Mov Disord 2007;22:297–308. doi: 10.1002/mds.21240
Nomura T, Inoue Y, Takigawa H, et al. Comparison of REM sleep behaviour disorder variables between patients with progressive supranuclear palsy and those with Parkinson’s disease. Parkinsonism Relat Disord 2012;18:394–396. doi: 10.1016/j.parkreldis.2011.10.018
Sobreira-Neto MA, Pena-Pereira MA, Sobreira EST, et al. High frequency of sleep disorders in Parkinson’s disease and its relationship with quality of life. Eur Neurol 2017;78:330–337. doi: 10.1159/000481939
Zuo LJ, Yu SY, Wang F, et al. Parkinson’s disease with fatigue: clinical characteristics and potential mechanisms relevant to α-synuclein oligomer. J Clin Neurol 2016;12:172–180. doi: 10.3988/jcn.2016.12.2.172
Hu Y, Yu SY, Zuo LJ, et al. Parkinson disease with REM sleep behavior disorder: Features, α-synuclein, and inflammation. Neurology 2015;84:888–894. doi: 10.1212/WNL.0000000000001308
Cao XY, Zhang JR, Shen Y, et al. Fatigue correlates with sleep disturbances in Parkinson disease. Chin Med J 2021;134:668–674. doi: 10.1097/CM9.0000000000001303

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