Parkinson's disease: an animated, cited guide

This page needs JavaScript for its animations. The outline and key answers are below, and every claim in the full version carries a numbered citation.

Not medical advice. Parkinson's Companion is an educational synthesis of published literature. It does not replace a clinician.

What is in it

What Parkinson's is Parkinsonism versus Parkinson's disease, who it affects, the numbers.
The dopamine pathway Substantia nigra to striatum, the go and brake loops, and what losing dopamine does.
Alpha-synuclein and Lewy bodies From a small synaptic protein to a Lewy body, and how it may spread.
How it spreads: Braak stages Six stages from the brainstem to the cortex, and the body-first debate.
Genes and inheritance LRRK2, GBA1, SNCA and parkin, founder populations, and what a test means.
Before the tremor Dream enactment, smell, constipation and the prodromal criteria.
Stages and symptoms Hoehn and Yahr, motor and non-motor symptoms, and how fast it moves.
Diagnosis and the MDS criteria The clinical criteria as a calculator, DaT scans and synuclein tests.
The differential Essential tremor, drug-induced parkinsonism, MSA, PSP and Lewy body dementia.
Levodopa and carbidopa From the pill to the striatum, step by step.
Levodopa over time Wearing-off, dyskinesia, the narrowing window and what smooths it.
The other medicines Agonists, MAO-B and COMT inhibitors, amantadine and the order of use.
Deep-brain stimulation Targets, the stimulation field, the beta rhythm and what the trials found.
Beyond movement Mood, hallucinations, dementia, sleep and blood pressure.
Risk and protection Pesticides, solvents, head injury, smoking, coffee and exercise.
Living with Parkinson's Exercise, therapy, falls, speech, work, caregiving and the end of life.
Nursing care Medicines on time, drugs to avoid, swallowing, assessment, documentation.
Toward a cure Synuclein antibodies, GLP-1 drugs, LRRK2 and GBA1, cells and genes.
History and people From James Parkinson's 1817 essay to the synuclein test.
Flashcards and mnemonics Flip cards by topic.
Quiz Questions with explanations.
Glossary Every term, searchable.
Sources Every reference behind the guide.

Part 4 · Living, caring, preventing

Risk and protection

Some chemicals, head injuries and family history are linked to a higher chance of Parkinson's; being physically active is linked to a lower one. Each row below is an association from observational studies, not proof of cause. Play the plot to bring the evidence in, then pick any row for the details and the caveats.

Age comes first. The strongest risk factor is age: yearly incidence rises from 0.1 per 100,000 under 40 to 133.9 at 80 and over, and men are affected more often than women. ^120,314 See What Parkinson's is.

Timeline

Dots are odds, hazard or risk ratios; lines are 95% confidence intervals, on a log scale. An arrow means the interval runs off the scale. A line that crosses 1 is compatible with no association. Click a row or use the buttons below.

From association to trial: neuroprotection tests

If a factor really protected the brain, raising or copying it might slow the disease. Randomised trials test that. Pick a test to see the observation that inspired it and what the trial found.

Test

Reveal

Bars are trial results as published. Higher scores mean more symptoms.

Observation	Trial	Result
Higher urate, lower risk (RR 0.43) ³⁷²	SURE-PD3: inosine in 298 people with early Parkinson's	Stopped early for futility; no slowing ³²⁵
Calcium-channel blockers inversely associated ²⁴⁷	STEADY-PD III: isradipine in 336 people for 36 months	No effect on progression (P = 0.85) ²⁹⁷
More activity, lower risk (RR 0.71) ⁹⁸	SPARX: high-intensity treadmill, 128 people, 6 months	Less motor worsening; only the high-intensity arm passed non-futility ³¹⁷
The same	Park-in-Shape: home aerobic cycling, 130 people, 6 months	4.2 points better than stretching, above the 3.5 threshold ³⁵⁸
The same	SPARX3: 80–85% versus 60–65% of maximum heart rate, 370 people	Active, not recruiting; primary completion estimated July 2027 ³⁴¹

What to take from it

Early evidence

Exercise: the one prevention message

A 2016 review concluded that promoting physical activity is the only intervention that currently seems justifiable for primary prevention of Parkinson's. ¹⁹ Exercise trials so far measured motor scores over 6 months; SPARX3 is testing intensity in a phase 3 trial that started on 30 August 2021. ^317,341,358 Exercise in daily life is covered in Living with Parkinson's.

Not advice

Smoking and coffee

The lower rates in smokers and coffee drinkers are associations. A Danish study found that former smokers who found quitting harder were less likely to develop Parkinson's, and the authors read "ease of quitting" as an early sign of the disease, not as proof that tobacco protects. ³⁰⁸ These findings are not advice to smoke or to drink coffee.

Early signs, not causes?

Constipation, anxiety, depression

In a meta-analysis, constipation was linked to later Parkinson's (RR 2.34, 1.55 to 3.53), as were anxiety and depression, but these may be early features of the disease rather than causes. ²⁴⁷ See Before the tremor.

Established

Family history and genes

A first-degree relative with Parkinson's gave OR 3.23 (2.65 to 3.93), and any relative OR 4.45 (3.39 to 5.83), the strongest factors in that meta-analysis. ²⁴⁷ How genes contribute is in Genes and inheritance.

Exam hookSmoking (RR 0.59 ever smokers) and coffee (RR 0.69) are inversely associated with Parkinson's; reverse causation and confounding are possible. Pesticides (paraquat, rotenone), trichloroethylene and head injury are linked to higher risk. Urate-raising inosine and isradipine failed as neuroprotection. ^{130,143,160,297,308,325,350}