Parkinson's disease is diagnosed clinically. A neurologist looks for slowness of movement (bradykinesia) together with a resting tremor or muscle stiffness, takes a careful history and examines how you move. No single test confirms the diagnosis; MRI, blood tests and a DaT-SPECT scan are used to rule out other causes when the picture is unclear.
How is Parkinson's disease diagnosed?
Parkinson's is diagnosed by a specialist from your symptoms, your medical history and a detailed physical examination. The NHS is explicit: "No tests can conclusively show that you have Parkinson's disease." MedlinePlus says the same, noting that because there is no specific test, diagnosis can be difficult.
The process usually starts with a general physician. The NHS says a GP will discuss your problems and may ask you to do simple mental or physical tasks, such as moving or walking. If Parkinson's is suspected, you are referred to a specialist, usually a neurologist or a geriatrician. The specialist watches you walk, turn, tap your fingers, rise from a chair and write, and checks for stiffness in your limbs.
The Cleveland Clinic describes the diagnosis as mainly clinical, based on medical history, a neurological examination and how symptoms change over time. Tests are ordered to exclude other conditions rather than to prove Parkinson's: blood tests, a brain MRI and, in some cases, a DaTscan. Genetic testing is used only when there is a strong family history. Newer laboratory tests for abnormal proteins are being studied but are not yet widely used.
Because the examination is the test, the experience of the examiner matters. If a diagnosis is uncertain, a second opinion from a neurologist who specialises in movement disorders is reasonable. You can search neurologists near you on HealthFinder.
What does a neurologist look for? The MDS criteria explained
The neurologist first confirms parkinsonism, then decides whether Parkinson's disease is its cause. The International Parkinson and Movement Disorder Society (MDS) criteria, published in 2015, formalise this. A 2017 validation study by Malek and colleagues in Parkinsonism and Related Disorders summarises the structure: the core definition of parkinsonism is bradykinesia with rigidity and/or rest tremor.
Once parkinsonism is present, three groups of features are weighed.
- Supportive criteria (four): a clear response to levodopa, levodopa-induced dyskinesia, rest tremor of a limb, and loss of smell.
- Absolute exclusion criteria: features that rule Parkinson's out, such as unequivocal cerebellar signs, vertical gaze palsy, parkinsonism confined to the legs, exposure to dopamine-blocking drugs, no response to high-dose levodopa, or normal dopamine imaging.
- Red flags: warning signs that point to another condition, such as rapid progression to a wheelchair, early recurrent falls, early severe autonomic failure, symmetric onset or absence of any non-motor symptoms.
The criteria give two levels of certainty. "Clinically established" Parkinson's needs two or more supportive criteria with no red flags; "clinically probable" allows red flags balanced by supportive features. In Malek's cohort of 2,000 recently diagnosed patients, 91.7% met the criteria: 63.1% established and 28.7% probable.
The NHS lists the three main symptoms the specialist is checking: tremor that usually begins in a hand or arm and is worse at rest, slowness of movement that can cause a shuffling walk, and muscle stiffness that makes movement and facial expression difficult.
What are the early signs of Parkinson's?
Early Parkinson's is subtle. The NHS says symptoms "usually develop gradually and are mild at first", and the Cleveland Clinic notes they usually start on one side of the body. The table combines the NHS symptom list with the Parkinson's Foundation's early signs and the caveats each gives.
| Early sign | What it looks like | Other common causes |
|---|---|---|
| Resting tremor | Slight shaking of a finger, thumb, hand or chin when relaxed | Stress, heavy exercise, some medicines |
| Small handwriting | Writing becomes smaller and cramped | Stiff fingers, poor vision |
| Loss of smell | Cannot smell strong foods; the NHS says this can precede other symptoms by years | Colds, sinus problems |
| Acting out dreams | Thrashing or shouting during sleep | Occasional restless sleep is normal |
| Stiffness or reduced arm swing | One arm does not swing when walking; feet feel stuck | Shoulder injury, arthritis |
| Constipation | Straining most days | Low fibre, low fluids, painkillers |
| Soft or low voice | Speech becomes quiet, breathy or hoarse | A chest cold |
| Masked face | Serious or sad expression without the mood | Some medicines |
The Parkinson's Foundation's caveat is sensible: no single sign means Parkinson's, but more than one is a reason to see a doctor.
Which tests rule out other causes of the symptoms?
Tests in Parkinson's are chosen to exclude look-alike conditions, because several other illnesses cause parkinsonism. The NHS lists drug-induced parkinsonism from some antipsychotics, which usually improves once the medicine is stopped; progressive supranuclear palsy, multiple system atrophy and corticobasal degeneration; and cerebrovascular disease, where a series of small strokes damages the brain.
- Brain MRI. The Cleveland Clinic lists MRI among the tests used to rule out other conditions. It can show strokes, hydrocephalus, tumours and some patterns seen in atypical parkinsonism; a normal MRI is the usual finding in Parkinson's itself. See our MRI scan cost guide for Indian prices.
- Blood tests. The Cleveland Clinic includes blood tests in the work-up. They screen for thyroid, liver and metabolic problems that can cause slowness or tremor.
- Medication review. Because dopamine-blocking drugs are an absolute exclusion criterion in the MDS framework, the neurologist checks every current and recent medicine, including those for nausea and psychiatric conditions.
- SPECT (DaT) scan. The NHS says a SPECT scan may be used in some cases "to try to rule out other causes of your symptoms". The next section explains when.
A response to levodopa is itself diagnostic information. A 2016 review by Umemura and colleagues in Neurologia medico-chirurgica states that an initial good response to levodopa is a good indicator of a correct diagnosis, and that atypical parkinsonism responds poorly. In the Malek validation cohort, a good levodopa response was recorded in 79.5% of clinically established cases.
What is a DaT-SPECT scan and when is it used?
A DaT-SPECT scan (DaTSCAN, ioflupane I-123) shows whether the dopamine nerve endings in the striatum are intact. A 2024 systematic review by Quintas and colleagues in Movement Disorders Clinical Practice explains that the tracer binds to presynaptic dopamine transporters in the putamen and caudate, so a reduced signal means loss of dopamine terminals, whatever the cause.
The scan is not routine. The review says it is useful when parkinsonism or tremor is clinically inconclusive, especially early, and that follow-up scanning is generally advised for uncertain diagnoses such as suspected essential tremor, drug-induced parkinsonism or vascular parkinsonism. A normal scan points away from Parkinson's and towards essential tremor, dystonic tremor, drug-induced or psychogenic parkinsonism.
Its accuracy has limits. The review reports that DaT-SPECT distinguishes Parkinson's patients from healthy people with roughly 90% sensitivity, but up to 15% of people meeting clinical criteria, particularly those with mainly upper-limb tremor, have normal scans. More importantly, an abnormal scan does not say which degenerative disease is present: the review describes "its limited capacity to distinguish between the different forms of degenerative parkinsonism", including multiple system atrophy and progressive supranuclear palsy. Antidepressants, anticholinergics and opioids can cause false positives.
The review concludes that diagnosis "must still be based on clinical criteria" and cites an estimate that about half of scans ordered by general neurologists add nothing, recommending that movement disorder specialists order them. Before paying for the scan, ask the neurologist whether the result would change management.
Why can a Parkinson's diagnosis take time?
Diagnosis takes time because the disease begins long before it is visible and because early symptoms overlap with other conditions. The NHS says nerve cell loss in the substantia nigra is gradual and symptoms usually begin only once "around 50% of the nerve cell activity" there has been lost. By the time a tremor appears, the process has been under way for years, yet the signs are still mild enough that the NHS warns a GP may not be able to say for certain whether you have the condition.
Even specialist diagnoses get revised. In the Malek cohort, 8.3% of people with a recent diagnosis did not meet the MDS criteria at baseline, and the group judged not to have Parkinson's grew to 18.2% at follow-up about 2.5 years later. The 2024 DaT-SPECT review cites autopsy confirmation rates for clinically diagnosed Parkinson's of 75% to 95%. In the EARLYSTIM surgical trial, reported by Artusi and colleagues in 2020, only 0.8% of carefully selected patients were later re-diagnosed.
So a neurologist may say "probable Parkinson's", start treatment and review the diagnosis over one to two years, watching for a sustained levodopa response and for red flags such as early falls or rapid decline.
In India, delay also happens before the first visit. A 2025 narrative review of Indian community studies by Khurana and Gourie-Devi in Cureus notes that patients often dismiss early, subtle signs such as tremor and rigidity, and that many patients and caregivers remain unaware of early symptoms, which delays medical intervention.
When should you see a neurologist?
See a doctor when you have more than one of the early signs above, or when a single sign such as a resting tremor, one-sided stiffness or a slowing walk persists for weeks without another explanation. The NHS advice is simple: see your GP if you are concerned you may have symptoms of Parkinson's disease; the GP decides whether to refer you to a specialist.
Ask for a neurologist referral directly if:
- a tremor is present at rest and eases when you use the hand
- one arm has stopped swinging when you walk, or your handwriting has shrunk
- a family member says you act out dreams, or you have lost your sense of smell without a cold
- you are taking an antipsychotic or an anti-nausea medicine and have developed slowness or stiffness
Take a list of every medicine you use and, if possible, a short phone video of the tremor or your walk, since symptoms may not show in the clinic.
Go to an emergency department or call 112 the same day if slowness, weakness or a tremor begins suddenly, affects one side with facial drooping or slurred speech, or comes with a severe headache. Sudden onset suggests a stroke, not Parkinson's.
A diagnosis of Parkinson's is distressing, and the NHS recommends support from family and a care team from the start. HealthFinder lists neurologists by city. This guide is general information from the sources listed below, not medical advice; a registered doctor makes decisions with you.
