Parkinson's disease is a progressive neurodegenerative disorder in which dopamine-producing neurons in the substantia nigra of the midbrain die off and abnormal alpha-synuclein protein accumulates as Lewy bodies. Roughly 1% of adults over 60 and up to 4% of adults over 80 develop the disease, and global cases exceeded 8.5 million in 2019 — more than double the figure from 1990 (GBD 2019).
Parkinson's disease (ICD-10: G20) is a progressive neurodegenerative disorder defined pathologically by the loss of dopaminergic neurons in the pars compacta of the substantia nigra and the accumulation of misfolded alpha-synuclein protein as intracellular Lewy bodies and Lewy neurites. The disease is the second most common neurodegenerative condition after Alzheimer's disease and the most common movement disorder in adults. Motor symptoms become clinically apparent only after roughly 50-70% of nigral dopaminergic neurons have already been lost and striatal dopamine is depleted by more than 60%, which is why the disease is often well advanced at diagnosis. Pathology is not limited to the substantia nigra: alpha-synuclein deposition begins in the olfactory bulb and lower brainstem (Braak stages 1-2), spreads to the midbrain and limbic system (stages 3-4), and reaches the neocortex in advanced disease (stages 5-6), which corresponds to the gradual emergence of cognitive and autonomic features.
The key symptoms of Parkinson's Disease are: Resting tremor at 4-6 Hz, classically a unilateral 'pill-rolling' tremor of the thumb and fingers that disappears with voluntary movement and worsens with stress — present in roughly 70% of patients at diagnosis., Bradykinesia, the cardinal slowing of voluntary movement, observed as small handwriting (micrographia), reduced arm swing on the affected side, shuffling steps, and a masked facial expression with reduced blinking., Rigidity with a 'cogwheel' or 'lead-pipe' quality felt on passive movement of the wrist or elbow, often accompanied by aching shoulder pain that can be misdiagnosed as frozen shoulder for months before tremor appears., Postural instability emerging after several years of disease, producing a stooped posture, festinating gait, and recurrent falls — a major driver of fracture and hospitalization in advanced disease., Gait freezing, in which the feet feel momentarily glued to the floor especially when starting to walk, turning, or passing through a doorway; freezing is a leading cause of falls and loses responsiveness to levodopa over time., Hypophonia and dysarthria, with a soft, monotone, slurred voice that the patient often perceives as normal while listeners struggle to hear — present in over 80% of patients within 5 years of diagnosis., Reduced sense of smell (hyposmia or anosmia), which precedes motor symptoms by 5-10 years in many patients and is now one of the most reliable prodromal markers..
Diagnosis of Parkinson's disease is clinical. The current standard is the Movement Disorder Society 2015 Clinical Diagnostic Criteria (Postuma 2015), which require the core motor syndrome of bradykinesia plus either rest tremor or rigidity, in combination with at least two supportive features (clear and dramatic response to levodopa, levodopa-induced dyskinesia, classical rest tremor, or olfactory loss / cardiac sympathetic denervation on MIBG scan), and the absence of any absolute exclusion criteria or red flags. The diagnostic workup begins with a detailed history that probes prodromal features — anosmia, RBD, constipation, depression — and a thorough neurological exam, particularly the MDS-UPDRS motor section. Brain MRI is recommended in essentially all new diagnoses, primarily to rule out vascular parkinsonism, normal-pressure hydrocephalus, and atypical parkinsonian syndromes; it is normal in classical Parkinson's. DaT-SPECT imaging (123I-FP-CIT, marketed as DaTscan) shows reduced striatal dopamine transporter binding and helps distinguish Parkinson's from essential tremor, drug-induced parkinsonism, and psychogenic tremor when the clinical picture is ambiguous; it does not separate Parkinson's from atypical parkinsonism. Response to a levodopa trial — at least 30% improvement on the MDS-UPDRS motor score with an adequate dose — is itself a supportive criterion. Genetic testing is offered selectively for young-onset disease, strong family history, or relevant ancestry (LRRK2, GBA panels). Skin biopsy for phosphorylated alpha-synuclein and seed amplification assays (RT-QuIC) on cerebrospinal fluid are increasingly available and approach 90% sensitivity in research settings. The AAN 2019 evaluation guideline emphasises serial reassessment over time, since the diagnosis is most reliably confirmed at follow-up two years later when atypical features have either appeared or stayed absent.
Parkinson's disease progresses slowly over years to decades. With modern medical, surgical, and rehabilitation care, life expectancy is close to that of age-matched peers for the first 10-15 years after diagnosis, and the gap widens mostly in late disease driven by dementia, falls, aspiration pneumonia, and frailty. Average disease duration from diagnosis to death is approximately 15-20 years, longer in young-onset and tremor-predominant subtypes and shorter in postural-instability gait-disorder and GBA-mutation carriers. Functional milestones used in counselling include time to motor fluctuations (median 5-7 years on levodopa), time to recurrent falls (median 9-10 years), and time to dementia (cumulative incidence ~25% at 10 years and up to 80% at 20 years). Predictors of faster decline include older age at onset, postural-instability gait-disorder subtype, GBA mutations, early autonomic dysfunction, and REM sleep behaviour disorder. Predictors of better outcome are tremor-dominant subtype, younger onset, strong levodopa response, sustained physical activity, and integrated specialist care.
A movement-disorder neurologist should evaluate any suspected new diagnosis to confirm Parkinson's, exclude atypical parkinsonian syndromes, and structure long-term care. Specialist input is also needed at every transition: when motor fluctuations or dyskinesias emerge, when cognitive or psychiatric symptoms appear, when assessing eligibility for DBS or focused ultrasound, and when planning end-of-life care. Population studies show that Parkinson's patients followed by a neurologist have lower mortality and lower nursing-home placement rates than those followed only in primary care (Willis 2011).
Find specialists →Parkinson's is a chronic progressive disease rather than one with recovery. After starting levodopa, most patients experience a clear motor improvement within days to a few weeks, with peak benefit reached at 4-8 weeks once doses are titrated. The first 3-5 years are often referred to as the 'honeymoon period' of stable response. Motor fluctuations and dyskinesias typically appear 5-10 years after starting levodopa. Following STN-DBS, motor improvement is apparent in the days after activation and continues to be optimised over the first 6-12 months as stimulation settings are refined and medication is reduced.
Aim for 150 minutes per week of moderate-to-vigorous aerobic activity (treadmill, cycling, swimming), two sessions of resistance training, and daily balance and flexibility work (tai chi, yoga, dance). The SPARX trial showed high-intensity treadmill training at 80-85% maximum heart rate slowed motor progression at 6 months. Tai chi reduces falls in Parkinson's by roughly 50% versus stretching. Boxing-style training programs (Rock Steady Boxing and similar) improve balance and quality of life. Exercise prescription should be tailored by a physiotherapist with Parkinson's experience and adjusted as disease progresses.
Look for board certification in neurology with a fellowship or substantial practice focus in movement disorders, regular use of the MDS-UPDRS, comfort interpreting DaT-SPECT, access to multidisciplinary rehabilitation (physiotherapy, occupational therapy, speech and language therapy), and a clear referral pathway to a DBS or focused-ultrasound centre when needed. Continuity over 10-20 years matters more than prestige — your neurologist should know your medication history and red-flag triggers in detail.
Medically reviewed by AIHealz Medical Editorial Board · May 12, 2026
Ranked by patient outcomes and specialized experience.
Verifying top specialists in Canada.
Apply as specialist →Specialists who treat Parkinson's Disease. Get expert guidance and personalized care.