What Is Parkinson's Disease? — An Orchestra Whose Conductor Is Fading, a First Beat That Comes In Late

"Why Are My Father's Hands Shaking?"

When I went home to my parents' house for the holiday, my seventy-two-year-old father is sitting on the couch watching television. His right hand, resting on his knee, is trembling faintly. As he reaches out to pick up the remote, the tremor subsides. When we go out for a walk, his pace is slower than before and his stride is narrow. My mother says that lately, in his sleep, he shouts and flails his arms. On the way back, one word lingers in my mind. Parkinson's disease.

Parkinson's disease is a condition where cells in the brain that help start and continue movements smoothly gradually decrease, making movements slower and smaller. The changes come from outside movement as well. Sense of smell, sleep, bowels, and mood change, and some of those come years before movement changes (PMID 18353132, PMID 32247370).

Starting from that hand tremor, this article looks at what this disease loses in the brain, what forms it comes in and how it is diagnosed, and how far medication, surgery, and exercise can help.

A Disease That Grows More Common, But Does Not Come to Everyone

Parkinson's disease increases steeply with age. Among 100,000 people, those with this disease numbered 41 in their 40s, 107 in their 50s, 428 in their 60s, 1,087 in their 70s, and 1,903 over the age of 80. This is the figure from an analysis collecting 47 studies published from 1985 to 2010, and in people in their 70s, there were differences depending on the region (PMID 24976103). Other reviews put it at 2 to 3% of those 65 and older, so estimates vary by data source (PMID 28332488), but by any estimate, it is a disease absent in the majority of older adults.

Globally, the number of people with this disease has grown, and that increase is greater than the share explained solely by the population aging. The drop in people dying from other diseases is cited as one reason for this. Whether the number of newly occurring cases itself is increasing is less certain. It is more common in older adults and men (PMID 38245248).

In most patients, the cause is unknown, and the form passed down within families accounts for only 5 to 15% of the total (PMID 31631455). Risk factors like pesticides and protective factors like a lifestyle involving a lot of physical activity are discussed, but because the disease progresses quietly for a long time before diagnosis, it is difficult to distinguish what the cause is (PMID 38245248).

Parkinson's disease increases with age, but it is a disease absent in the majority of older adults.

Shrinking Cells, Clumping Proteins

If you examine the brain of someone who had Parkinson's disease after death, two changes stand out. Nerve cells have vanished from a specific spot deep in the brain, and inside the remaining cells are clumps of misfolded protein (PMID 31631455).

A nerve cell is a basic cell of the brain and nerves that receives electrical signals and passes them on to the next cell. A synapse is the joint where one nerve cell passes a signal to the next nerve cell.

A neurotransmitter is a chemical substance that a nerve cell releases to send signals to other cells, usually crossing from the synapse to the cell on the other side. Dopamine is a neurotransmitter that nerve cells deep in the brain produce and send to a wide area, and it is involved in movement, learning, and drive. The event that leads to a diagnosis of this disease is usually movement among those, but changes in drive and mood can come before movement symptoms (PMID 42208351).

The brainstem is the stem-like part at the very bottom of the brain that connects toward the neck. The substantia nigra is a small cluster of nerve cells in the upper part of the brainstem that makes dopamine and sends it to the basal ganglia deep in the brain.

The basal ganglia are clusters of nerve cells gathered deep inside the cerebrum that form a circuit for starting and selecting movements.

What disappears in Parkinson's disease is the dopamine-producing nerve cells of the substantia nigra. When these cells shrink, the dopamine reaching the basal ganglia drops sharply, and the circuits of the basal ganglia get scrambled so that movement does not work properly (PMID 41904982).

This loss proceeds quietly for a long time. Movement symptoms appear only around the time when about half of the dopamine nerve cells in the substantia nigra have vanished, and it is estimated to take anywhere from 5 to 20 years from when the cells start dwindling to when movement symptoms appear. This value is calculated by working backward from post-mortem studies and imaging studies (PMID 22981298).

What makes up the clumps inside the remaining cells is alpha-synuclein. Alpha-synuclein is a protein inside nerve cells that, in Parkinson's disease, adopts the wrong shape and clumps together with others. The accumulation of these clumped masses inside nerve cells is a hallmark of the disease, along with the loss of substantia nigra cells (PMID 31631455).

The changes do not stay only in the substantia nigra. The autonomic nervous system is the nervous system that regulates organs we cannot move at will, such as the heart, blood vessels, organs, and glands. Various cells in other parts of the brain and throughout the autonomic nervous system are affected together, probably from early in the disease (PMID 28332488). It is not yet fully understood why these specific cells break down first (PMID 42208351).

Comparing it to an orchestra helps make this sequence clear. The band members each know how to play their instruments, but they match when to come in and how loud to play by watching the conductor. If the muscles and the nerves that tell the muscles to move are the band members, the basal ganglia are the podium, and the dopamine coming from the substantia nigra is the beat traced by the conductor's baton. In Parkinson's disease, the band members remain the same, but the conducting becomes blurred. You can still play, but the first beat comes in late, the sound grows softer, and the piece steadily slows down.

The analogy holds true only up to that point. Tremor cannot be explained by this picture alone. Other circuits outside the basal ganglia are also tangled up in tremor, and that principle is not yet fully understood (PMID 36211804). And alpha-synuclein clumps also form in the pathway that smells and the nerves of the gut (PMID 22981298, PMID 32737460). Symptoms coming from those spots have nothing to do with the podium.

Parkinson's disease is a condition where the dopamine nerve cells in the substantia nigra slowly dwindle and alpha-synuclein clumps accumulate inside them, and movement symptoms appear only after those cells have already vanished by about half.

What We See Before the Tremor, the Slowing

There is one symptom that must be present for a diagnosis of Parkinson's disease. It is a slowing of movement. A diagnosis is made when this slowing is accompanied by either a resting tremor or rigidity, and the medical history and examination suggest no other cause (PMID 30704685).

Bradykinesia is a symptom where movements become slow and small, and it becomes difficult even to initiate movement. Diagnosis relies on the presence of this symptom (PMID 28332488).

Resting tremor is a tremor that appears when the limbs are relaxed and at rest. The typical tremor of Parkinson's disease is a resting tremor biased toward one side (PMID 17724978).

Rigidity is a state in which muscles are stiffly set, so that when someone else tries to bend and straighten a limb, resistance is felt throughout the entire movement. It is different from spasticity, which has a similar name. Spasticity is a state in which the reflex of pulling back and contracting when a muscle is stretched becomes excessively large, so that the faster the muscle is stretched, the harder the resistance feels. Rigidity resists regardless of speed.

Postural instability is a weakening of the ability to correct one's posture to avoid falling when the body tilts or is pushed. Along with tremor, rigidity, and bradykinesia, it has long been counted as one of the four representative motor symptoms of Parkinson's disease (PMID 31631455), but the revised diagnostic criteria removed it from the core symptoms (PMID 28150045). Problems with gait, balance, and posture usually become prominent at an advanced stage of the disease (PMID 38036102).

Reading these criteria backward reveals two things. Even if your hands do not shake, if you have slowing and rigidity, it may be Parkinson's disease. Even if your hands shake, if there is no slowing of movement, it does not fit these criteria (PMID 30704685). The combination and appearance of symptoms vary from patient to patient (PMID 40748114).

The center of Parkinson's disease diagnosis is the slowing of movement rather than tremors, and the mere fact that hands shake does not tell you whether it is Parkinson's disease.

Signals That Come Before Movement

Some people experience a loss of sense of smell, acting out dreams during sleep, long-standing constipation, and depression before any movement symptoms appear. Direct evidence has accumulated showing that these four can be in the pre-diagnosis stage (PMID 22508280).

The prodromal stage is a period when changes from the disease have already begun, but movement symptoms strong enough to make a diagnosis have not yet appeared. This period lasts for many years and involves brain areas outside the substantia nigra, neurotransmitters outside dopamine, and nerves outside the brain and spinal cord together (PMID 32247370). Loss of smell and REM sleep behavior disorder can precede movement symptoms by as long as several decades (PMID 38517805, PMID 22981298).

REM sleep is a sleep state where the eyes move rapidly beneath closed eyelids, most of the body's muscles are relaxed and do not move, and people have many vivid dreams. REM sleep behavior disorder is a condition where the muscles that should be relaxed during REM sleep fail to relax, causing a person to act out their dreams with their actual body. What REM sleep is continues in "Sleep Stages and Sleep Cycles — Dives into Deep Water, and a Sleep No Depth Gauge Can Measure".

Among the prodromal signals, the one with the greatest weight is REM sleep behavior disorder, which is considered a marker that predicts Parkinson's disease with very high probability (PMID 32247370). It is estimated that people who have only REM sleep behavior disorder without other conditions are at very high risk of developing a disease where nerve cells break down if followed for a long time, and that disease category includes other conditions where alpha-synuclein accumulates. Because there is still no treatment to change or slow its progression, the long prodromal stage is regarded as an opportunity to start treatment early in the future (PMID 37180094). Whether nighttime body movements are this disease is confirmed through clinical examination and tests.

The other signals are in a different situation. Reduced sense of smell and some autonomic symptoms are common enough to already be present in most patients at the time of diagnosis, but apart from REM sleep behavior disorder and certain autonomic markers, no single sign is specific enough to single out the prodromal stage on its own (PMID 22508280). Finding the prodromal stage through an olfactory test requires adding other tests (PMID 23279440). Having constipation, depression, or a reduced sense of smell alone does not make it known whether the condition leads to Parkinson's disease, and that judgment is made through clinical examination and tests.

Although alpha-synuclein clumps have been found in gut nerves even before diagnosis, leading to the view and model that the disease begins in the gut or the olfactory pathway and spreads (PMID 32737460, PMID 37062013), this remains a hypothesis under validation.

Non-movement symptoms persist even after diagnosis and increase as the disease progresses. There are mood changes such as apathy and depression, decline in thinking power and hallucinations, and sleep problems, while sensory problems such as reduced sense of smell and pain are present in almost all patients. Autonomic problems such as blood pressure dropping when standing up, urinary problems, and constipation are also present to some degree in most patients (PMID 18353132). Although these symptoms greatly influence quality of life, they tend to be addressed less in clinical care (PMID 26372623).

As the disease progresses, alpha-synuclein clumps spread throughout the cerebrum (PMID 28150045). Dementia with Lewy bodies is dementia that occurs as clumps formed by the aggregation of a protein called alpha-synuclein develop inside nerve cells. It is a disease of the same branch as Parkinson's disease (PMID 37062013), and is covered in "What Is Dementia? — Snow That Settles Without a Sound, a Branch Beginning to Bend".

Parkinson's disease begins several years ahead of movement symptoms, and reduced sense of smell, REM sleep behavior disorder, constipation, and depression can come first, but except for REM sleep behavior disorder, Parkinson's disease cannot be singled out by any single one of those signals alone.

Diagnosis Happens in the Exam Room

There is no definitive test that confirms Parkinson's disease in a living person. Genetic testing in specific situations is an exception, and its use is limited to a small number of patients (PMID 31625879). Diagnosis is made primarily through a physical examination (PMID 31631455).

The 2013 diagnostic recommendations from the European neurological community note that diagnosis still relies heavily on properly recognizing the clinical features of this disease, with genetic, olfactory, and imaging tests serving as supportive roles to assist the diagnosis (PMID 23279440). When it is uncertain whether alpha-synuclein is the disease protein that is accumulating, a test to remove a tiny piece of skin and stain it for alpha-synuclein is now also available (PMID 40748114).

The tremors most commonly encountered in the clinic are essential tremor and Parkinson's disease tremor (PMID 35180133). Essential tremor is a condition where, without any other disease, tremor occurs mainly while using the hands, such as when stretching the arms forward or holding a cup. It usually affects both sides similarly, and there is often a family history of the same tremor. This distinction is important because the two diseases have different prognoses and treatments (PMID 17724978).

This distinction is not always neat. Some Parkinson's disease patients also have tremors when using their hands, and some essential tremor patients have much more pronounced trembling on one side (PMID 17724978). Distinguishing between the two is especially difficult in the early stages of the disease (PMID 35180133). This is why you cannot judge based solely on the appearance of the tremor at home. When certainty is lacking, imaging tests that illuminate whether dopamine nerve cells have decreased are used to separate the two (PMID 23279440).

Movement symptoms resembling Parkinson's disease can also be caused by other degenerative diseases or certain psychiatric medications, and imaging tests are used to separate these causes as well (PMID 23279440). Diagnoses also change over time. A not-insignificant percentage of patients had their antemortem Parkinson's disease diagnoses unconfirmed at autopsy, and revised diagnostic criteria were introduced to improve this accuracy (PMID 28150045).

Parkinson's disease is diagnosed through physical examination, and tests help separate it from mimicking conditions like essential tremor.

Medicines That Fill the Gap in Dopamine

More than 50 years have passed since levodopa was first used. Although various drugs have emerged since then, levodopa remains the most effective medication for movement symptoms and works across all stages of the disease (PMID 36342310).

Levodopa is a class of medication that supplies raw material entering the brain to turn into dopamine, filling the shortage of dopamine. Dopamine agonists are a class of medication that attach directly to the receptors that receive dopamine, mimicking its signals. Comparing this to an orchestra, it is like calling out the tempo of a fading conductor from the outside.

A review published in 2018 by the International Parkinson and Movement Disorder Society (MDS), gathering the highest-grade trials, judged both of these classes to be clinically useful in the early stages (PMID 29570866). The evidence that both classes help with movement symptoms at all stages of the disease is strong, and drugs that prevent the breakdown of dopamine are also used (PMID 24756517). Most movement symptoms are managed to an acceptable level by these dopamine medications (PMID 36342310).

Benefits come with limits and side effects. Some people find that tremors respond less to dopamine drugs than other symptoms do (PMID 36211804). Nausea, psychiatric symptoms such as hallucinations, and behaviors where urges cannot be controlled are cited as side effects, and impulse control problems are usually managed by the prescribing physician reducing or stopping dopamine medications, particularly dopamine agonists (PMID 24756517). Furthermore, these drugs ease symptoms but cannot change the underlying process in which nerve cells dwindle (PMID 31631455, PMID 24756517).

For several years after treatment begins, a period where the medication works evenly continues, commonly called the honeymoon period. After using levodopa for two or three years, responses to the medication begin to waver (PMID 36342310).

Motor fluctuations are when times of moving well after taking medication and times when the drug wears off and the body stiffens again alternate within a day. The time the medication works grows shorter, and the degree to which it helps becomes unreliable (PMID 32761324). Recognizing and managing these fluctuations early helps quality of life greatly (PMID 36342310). Dyskinesia refers to unintended body movements that occur on their own, and in Parkinson's disease, it mainly appears after using levodopa for a long time. It usually appears after years of treatment, but rarely is seen after just days or months (PMID 29503325).

Comparing this to an orchestra, the tempo becomes clear and then blurs depending on the drug's effect, and sometimes notes not on the score creep in. These motor complications are related to dopamine-replacing medications entering the brain intermittently (PMID 23948989). To manage them, the physician must periodically readjust the timing and combination of medications (PMID 36342310), and there are also several drugs that ease fluctuations and reduce dyskinesia (PMID 29570866).

When and with which drug to start depends on the severity of symptoms and age. If symptoms are mild, tremors are the most prominent, or the patient is under 60, treatment may begin with a different drug first to avoid motor complications caused by levodopa (PMID 24756517), whereas for younger patients for whom continuing work and activities is important, levodopa is started early (PMID 23948989). That choice is determined by the prescribing physician tailored to each individual patient (PMID 29570866).

Decisions to reduce or stop Parkinson's disease medications are made by the prescribing physician. Stopping these drugs abruptly or cutting them back drastically can cause a dangerous complication—though rare—involving high fever, severe rigidity, and lowered consciousness. Among patients who developed this complication, deaths of up to 4% have been reported, and about one-third suffered permanent aftereffects. Recognizing and managing it early improves the prognosis, and this complication must always be kept in mind when a person with Parkinson's disease experiences a sudden and severe worsening of symptoms (PMID 18712508). Other dangerous complications have also been reported in cases where patients drastically increased their medication on their own (PMID 35811538).

Levodopa has been the most effective Parkinson's disease medication for over 50 years, but after a few years, it is common for its effects to become erratic or for unintended movements to arise, and it does not halt the progression of the disease itself.

The Road After Medication, Deep Brain Stimulation

There are people whose bodies lock up and loosen multiple times a day no matter how well their medications are adjusted, and whose involuntary movements are distressing. For such patients, deep brain stimulation has become a well-established treatment (PMID 31512617).

Deep brain stimulation is a surgery in which thin electrodes are placed deep inside the brain and a device implanted in the body continuously sends weak electrical stimulation to relieve movement symptoms. The factors that best predict the benefits of surgery are whether the stiffness responds well to levodopa, normal thinking capacity, and a younger age (PMID 18267284).

A 2022 guideline published by the European Academy of Neurology (EAN) and the MDS European Section graded the evidence separately for each stimulation target. For advanced patients whose fluctuations are not well controlled by oral medication, stimulation of the subthalamic nucleus—the most studied target—improves movement symptoms and quality of life better than current drug therapy alone, so it should be offered to eligible patients, and stimulation of another target (the globus pallidus) may also be offered. It was considered that stimulation could be offered even to patients at an early stage who develop fluctuations early, whereas it was not recommended for early-stage patients without fluctuations. The guideline's conclusion is that the evidence for invasive treatments as a whole is mixed and has been tested only in specific patient populations (PMID 35791767).

This surgery is also not offered as a treatment that cures the disease or stops its progression, which is noted as an essential point to inform patients considering the surgery (PMID 31512617). The most common side effect is slurred speech, and as the disease progresses, axial symptoms such as balance and gait become less responsive to stimulation (PMID 35798568).

Deep brain stimulation improves symptoms and quality of life for some patients with fluctuations that cannot be controlled by medication, but it does not halt the progression of the disease.

What Exercise Does

In a 2024 analysis gathering 154 randomized trials, movement symptoms were compared by pooling 60 of those trials (2,721 people) and quality of life by pooling 48 trials (3,029 people). Most exercises improved movement symptoms and quality of life compared to a non-exercising control group (PMID 38588457). The evidence for these benefits has accumulated, and the certainty of that confidence was moderate or lower.

The magnitudes are also available. Dance lowered the movement symptoms score by about 10 points (10.18 points), and gait and balance training lowered it by about 7.5 points (7.50 points). In this scoring system, a reduction of more than 2.5 points is considered a difference that patients can feel, and both results were evaluated with moderate certainty. The authors concluded that because there is little evidence showing differences between types of exercise, exactly which exercise it is may be secondary, which also aligns with the possibility that Parkinson's-tailored programs are most effective for specific movement symptoms. They also noted that larger, better-designed studies are needed to increase certainty (PMID 38588457).

The limitations are also in the same analysis. Most participants were people with mild to moderate stages and without major cognitive impairment, and the number of participants per trial was small, averaging 51. The most frequently reported adverse events were falls and pain, and while it is very uncertain whether exercise alters the risk of adverse events, the exercises in the trials were described as relatively safe (PMID 38588457).

Physical therapy is a treatment that builds the ability to move and transfer the body—such as sitting, standing, walking, and balancing—through exercise and training, and sometimes uses physical modalities like heat and electricity for pain or movement. A 2018 review by the MDS judged physical therapy to be clinically useful as an add-on treatment after medication has been optimized (PMID 29570866). Guidelines recommend receiving physical therapy consistently from an early stage, and various symptoms, including falls, can improve (PMID 40185529).

Although there is an expectation that exercise can slow the progression of the disease itself, it has not yet been confirmed. A 2024 review reported that the evidence to date supports exercise as a treatment with the potential to alter the disease course, and suggested prescribing exercise alongside medication from an early stage (PMID 38418216). Other reviews also viewed that exercise could alter the course, but noted that research is limited because exercise methods and measurements vary (PMID 40185529) and more studies are needed to confirm it (PMID 29027544).

Evidence on the preventive side comes from observation. An association where people who move their bodies a lot develop Parkinson's disease less often has been reported, and a 2016 review considered that the only intervention justifiable right now as primary prevention is encouraging physical activity. This was because of the reason that it would also be beneficial in preventing various chronic diseases (PMID 27751556). However, because the disease progresses for a long time before diagnosis, there is a high risk in these associations that cause and effect may appear reversed (PMID 27503097).

Evidence has accumulated through randomized trials that exercise improves movement symptoms and quality of life in Parkinson's disease, but whether it slows disease progression has not yet been proven.

What Is Not Yet Here, and Treatments That Slow Progression

Over the past 20 years, several high-quality trials have tried to slow progression, but failures have piled up as treatments that showed promise in experimental models failed to translate into human success (PMID 35296034). A 2018 review by the MDS concluded that there were no clinically useful interventions to stop or slow the disease's progression (PMID 29570866), and a 2025 review similarly noted that there are still no clear progression-modifying interventions (PMID 40748114).

Methods to block or reverse the buildup of alpha-synuclein, as well as methods using stem cells or growth factors to revive lost nerve cells, are being studied (PMID 40868817). All of these are still in the research phase. By the time movement symptoms appear, about half of the dopamine nerve cells in the substantia nigra have already vanished (PMID 22981298), and finding markers to spot the prodromal phase so that new treatments can be started earlier is considered a major challenge in this field (PMID 28332488).

Even so, much can be done. Lifestyle changes, medications, and surgery can improve symptoms and quality of life (PMID 40748114), and levodopa remains effective across the entire course of the disease (PMID 36342310).

Treatments that slow progression are not yet proven, but treatments that ease symptoms and raise quality of life span the entire course of the disease.

Again, My Father's Right Hand

Let us return to the father at the beginning. His right hand trembles when he rests, his walk has slowed and his step narrowed, and he flails his arms in his sleep. Trembling in one hand at rest is a classic feature of Parkinson's disease tremors (PMID 17724978), but a tremor alone cannot determine what the condition is. Diagnosis requires a slowness of movement, and confirming that relies on a physical examination (PMID 30704685).

The examination goes hand in hand with separating conditions that look similar, such as essential tremor, and if confusion remains, imaging tests that illuminate dopamine nerve cells are helpful (PMID 23279440). The behaviors in sleep may be REM sleep behavior disorder. European diagnostic guidelines recommend checking for REM sleep behavior disorder, thinking ability, and severe depression together during the initial evaluation of someone suspected of having Parkinson's disease (PMID 23279440).

If diagnosed with Parkinson's disease, levodopa-class medications can be expected to manage most movement symptoms, and fluctuations in drug efficacy may arrive a few years later (PMID 36342310). For some people, tremors respond less than other symptoms do (PMID 36211804). The decision to reduce or change medication is made by the prescribing doctor, and stopping abruptly can be rare but dangerous (PMID 18712508). If fluctuations are not managed by medication, deep brain stimulation may come up as a topic, but that is also a treatment for select patients chosen by weighing their response to medication, thinking ability, and age (PMID 18267284, PMID 35791767).

Physical therapy is recommended from an early stage (PMID 40185529), and there is evidence that exercise improves movement symptoms and quality of life. Most of that evidence has come from patients in mild or moderate stages, and whether progression can be slowed by exercise has not yet been confirmed (PMID 38588457, PMID 29027544). Which tests to receive and which treatments to choose are matters to be decided together with a doctor in the clinic.

Where to Look Further

Trials seeking treatments to slow progression are still ongoing, and what to learn from past failures is the question in this field (PMID 35296034). Whether exercise changes the course of the disease and how accurately people in the prodromal phase can be identified are also still open questions (PMID 29027544, PMID 32247370).

Dopamine and synapses continue in "How Do Nerve Cells Send Signals? — A Burning Fuse, a Gap Crossed by Ferry", and the locations of the brainstem and cerebrum in "The Map of the Brain — Neighborhoods with Their Own Jobs, a City Joined by Roads". Spasticity, which is easy to confuse with rigidity, can be seen in "One Word, "Spasticity" — Reading the Upper Motor Neuron Syndrome Apart".

Why exercise and training are structured that way continues in "Why Therapy Is Designed That Way — An Introduction to Motor Learning Principles", and why a single prodromal sign like an olfactory test is not enough in "What a Test Actually Tells You — An Introduction to Sensitivity, Specificity, and Pretest Probability". Other diseases of the brain and nerves continue in "Headache and Migraine — A Bell That Rings Easily, a Threshold That Falls as Attacks Grow Frequent", "What Is Epilepsy? — Windows Lit One by One, Lights That Flash All at Once", and "Numbness and Peripheral Neuropathy — The Long Supply Line That Runs Short at the Farthest Village, the Sock That Climbs From the Toes".

Source Papers

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• "The epidemiology of Parkinson's disease." (2024) — PMID 38245248 — Prevalence is increasing beyond population changes (due to decreased competing causes of death, etc.); the increase in incidence is less certain; it is common in older adults and men; causes are multifactorial; the causality of risk and protective factors is difficult to untangle due to a long prodromal period.
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• "Opportunities and Pitfalls of REM Sleep Behavior Disorder and Olfactory Dysfunction as Early Markers in Parkinson's Disease." (2024) — PMID 38517805 — REM sleep behavior disorder (loss of REM sleep muscle atonia, dream enactment behavior) and hyposmia can precede motor symptoms by decades; opportunities and pitfalls as early markers.
• "Considering REM Sleep Behavior Disorder in the Management of Parkinson's Disease." (2023) — PMID 37180094 — Isolated REM sleep behavior disorder carries a very high risk of developing neurodegenerative disease on long-term follow-up (a prodromal manifestation of alpha-synucleinopathy); there is no disease-modifying treatment.
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• "The brain-first vs. body-first model of Parkinson's disease with comparison to alternative models." (2023) — PMID 37062013 — Parkinson's disease and dementia with Lewy bodies are Lewy body diseases; SOC model: alpha-synuclein starts in one location (enteric nervous system or olfactory system) and spreads in the majority; body-first leads to pre-diagnostic autonomic symptoms and REM sleep behavior disorder (the authors' model).
• "[Parkinson's Disease: Clinical Review and Update]." (2019) — PMID 31625879 — Except for genetic testing in specific situations, there is no method for definitive diagnosis during life; diagnosis relies on clinical findings and is supported by tests.
• "EFNS/MDS-ES/ENS [corrected] recommendations for the diagnosis of Parkinson's disease." (2013) — PMID 23279440 — Diagnosis relies heavily on clinical features, with genetic, olfactory, and imaging tests as adjunctive; recommending screening for cognition, REM sleep behavior disorder, psychotic symptoms, and severe depression at the first evaluation; olfactory screening requires additional tests; dopamine transporter imaging is used when uncertain, such as to differentiate degenerative parkinsonism from essential tremor or when exposed to neuroleptics.
• "Differentiating Parkinson's Disease from Essential Tremor Using Transcranial Sonography: A Systematic Review and Meta-Analysis." (2022) — PMID 35180133 — Essential tremor and Parkinson's disease tremor are the most common tremors in clinical practice, and distinguishing them is difficult, especially in early stages.
• "Pharmacological management of Parkinson's disease motor symptoms: update and recommendations from an expert." (2022) — PMID 36342310 — Levodopa has been the most effective for over 50 years with sustained benefit throughout the disease course; most motor symptoms are managed with dopamine medications; fluctuations begin after 2 to 3 years (after the honeymoon period); periodic medication adjustments are necessary; neuroprotective effects are unproven.
• "International Parkinson and movement disorder society evidence-based medicine review: Update on treatments for the motor symptoms of Parkinson's disease." (2018) — PMID 29570866 — Re-reviewed 143 Level I studies; no clinically useful interventions to stop or slow progression; dopamine agonists, levodopa, and others are useful for initial monotherapy; physical therapy is useful, exercise-based training is possible; various drugs and bilateral deep brain stimulation are useful for fluctuations and dyskinesia; individual patient selection is up to the treating physician.
• "Pharmacological treatment of Parkinson disease: a review." (2014) — PMID 24756517 — Levodopa is the most effective, but other drugs may be started first for mild symptoms, tremor predominance, or age under 60; side effects (nausea, psychosis, impulse control disorders — managed by reducing or stopping dopamine drugs, especially agonists); strong evidence for levodopa and agonists; no treatment alters the degenerative process.
• "Medical Management and Prevention of Motor Complications in Parkinson's Disease." (2020) — PMID 32761324 — Levodopa is the most effective; over time, the duration and reliability of the response decrease (motor fluctuations), along with levodopa-induced dyskinesia.
• "Parkinson's disease: A review." (2018) — PMID 29503325 — Levodopa-induced dyskinesia usually occurs after prolonged treatment, and rarely after days to months.
• "Levodopa in the treatment of Parkinson's disease: current status and new developments." (2013) — PMID 23948989 — Levodopa is a dopamine precursor; it is sometimes started early to maintain work and activities in younger patients; motor complications are related to intermittent delivery.
• "The parkinsonism-hyperpyrexia syndrome." (2009) — PMID 18712508 — Rare but can be fatal; often after reduction or cessation of medication; rigidity, high fever, altered consciousness; mortality up to 4%, permanent sequelae in one-third; prognosis improved by early recognition and management; warns against sudden dose reduction (case reports and review).
• "Parkinsonism-Hyperpyrexia Syndrome and Dyskinesia-Hyperpyrexia Syndrome in Parkinson's Disease: Two Cases and Literature Review." (2022) — PMID 35811538 — Cases of dyskinesia-hyperpyrexia syndrome associated with medication abuse (case report and literature review).
• "Deep Brain Stimulation in Parkinson's Disease." (2019) — PMID 31512617 — An established treatment for fluctuations and dyskinesia not controlled by the best medical therapy; patients must be informed that it is not provided as a cure or to halt progression.
• "Deep brain stimulation for Parkinson's disease." (2007) — PMID 18267284 — Predictors of surgical benefit: levodopa responsiveness, normal cognition, young age.
• "European Academy of Neurology/Movement Disorder Society-European Section Guideline on the Treatment of Parkinson's Disease: I. Invasive Therapies." (2022) — PMID 35791767 — 2022 European guidelines: subthalamic nucleus stimulation improves motor function and quality of life in advanced patients whose fluctuations are not controlled by medication, and should be offered to eligible patients; not offered to early patients without fluctuations.
• "Deep brain stimulation for Parkinson's disease." (2022) — PMID 35798568 — The most common side effect is dysarthria; axial trunk symptoms respond less as the disease progresses.
• "Physical exercise for people with Parkinson's disease: a systematic review and network meta-analysis." (2024) — PMID 38588457 — 154 randomized trials involving 7,837 people (mostly mild to moderate, no major cognitive impairment, mean 51 people); most exercises improve motor symptoms and quality of life compared to passive controls; dancing −10.18 (minimal clinically important difference −2.5, moderate certainty); small differences between types; side effects very uncertain, falls and pain most frequent, relatively safe; authors' conclusion: exact type may be secondary, consistent with the possibility that dedicated programs are most effective for specific symptoms, larger studies needed. Movement analyses 60 trials 2,721 people, quality of life 48 trials 3,029 people. Revised version of the 2023 edition of the same analysis (PMID 36602886) — values based on this edition (search May 2021).
• "Physiotherapy and Exercise in Parkinson's Disease." (2025) — PMID 40185529 — Guidelines recommend early and consistent physical therapy referral; falls and other issues can be improved; exercise may alter the course, but studies are limited by heterogeneous interventions and measurements.
• "Long-term effects of exercise and physical therapy in people with Parkinson disease." (2017) — PMID 29027544 — Effects of 4 weeks of gait training and 8 weeks of balance training last 3 to 12 months; disease-modifying effects require further study.
• "Exercise as medicine in Parkinson's disease." (2024) — PMID 38418216 — Medications do not stop progression; reporting that exercise is supported as primary prevention, a potential disease-modifying therapy, and symptomatic treatment, suggesting individualized prescription from an early stage (authors' paradigm shift proposal).
• "The epidemiology of Parkinson's disease: risk factors and prevention." (2016) — PMID 27751556 — Association of physical activity and other factors with lower risk; the only intervention justifiable as primary prevention is encouraging physical activity (which is also beneficial for preventing multiple chronic diseases).
• "Prodromal symptoms of Parkinson's disease: Implications for epidemiological studies of disease etiology." (2016) — PMID 27503097 — Reverse causality is a major concern in many reported associations due to the long prodromal period.
• "The Disease Modification Conundrum in Parkinson's Disease: Failures and Hopes." (2022) — PMID 35296034 — Over the past 20 years, effective disease-modifying therapies in preclinical models have failed to translate into clinical success, leading to accumulated failures; halting progression remains the "Holy Grail".
• "The Search for Disease Modification in Parkinson's Disease-A Review of the Literature." (2025) — PMID 40868817 — Examining approaches like preventing or reversing alpha-synuclein accumulation, oxidative stress and immune modulation, and neuronal regeneration with stem cells and growth factors; difficulty in recruiting prodromal patients.