Parkinson's Disease — Symptoms, Causes & Treatment | MyMedicPlus

Parkinson's disease (PD) is the second most common neurodegenerative disease worldwide after Alzheimer's disease, affecting approximately 10 million people globally — with a global prevalence projected to more than double to 12 million by 2030 as populations age. PD arises from progressive, selective degeneration of dopaminergic neurons in the substantia nigra pars compacta — a midbrain nucleus projecting to the striatum via the nigrostriatal pathway — causing severe striatal dopamine deficiency that drives the characteristic motor syndrome. The pathological hallmark is the accumulation of intraneuronal Lewy bodies — spherical cytoplasmic inclusions containing aggregated, misfolded alpha-synuclein protein — which propagate in a predictable caudal-to-rostral pattern through the nervous system (Braak staging, stages 1-6), explaining the sequential development of non-motor then motor symptoms over years to decades. Diagnosis requires the presence of bradykinesia (slowness and reduced amplitude of repetitive movements) plus at least one of resting tremor or rigidity (UK Brain Bank criteria). PD onset is typically in the sixth to seventh decade (median age 60-65 years), with only 5-10% of cases classified as young-onset PD (onset before 50 years — more likely to have an identified genetic cause). Men are 1.5 times more likely to develop PD than women. The prodromal (pre-motor) phase — during which Lewy body pathology has already started but motor symptoms are absent — may span 5-20 years, during which anosmia, REM sleep behaviour disorder, constipation, and depression represent early biomarkers.

PD aetiology is complex, arising from an interaction of genetic susceptibility, environmental exposures, and ageing-related changes in cellular proteostasis and mitochondrial function. Genetic forms (~10-15% of PD): LRRK2 (Leucine-rich repeat kinase 2 — the most common pathogenic variant in autosomal dominant PD, accounting for 1-2% of sporadic and 4-5% of familial PD; G2019S mutation occurs in 40% of PD in Ashkenazi Jewish and North African Berber populations); SNCA (alpha-synuclein gene — point mutations and gene triplication/duplication causing early-onset PD); Parkin (PARK2 — autosomal recessive, most common genetic cause of young-onset PD before age 40, slowly progressive); PINK1 and DJ-1 (PARK7 — recessive, young-onset, mitochondrial pathway dysfunction); and GBA mutations (glucocerebrosidase gene variants, present in 5-15% of PD, increasing risk 5-15x and associated with faster cognitive decline). Environmental risk factors: chronic pesticide exposure (rotenone and paraquat — organophosphates and herbicides used in agriculture, strongly linked in epidemiological studies, replicate alpha-synuclein aggregation in animal models); head trauma (cumulative traumatic brain injury increasing PD risk); rural living and drinking well water; industrial solvents (trichloroethylene). Protective factors — associated with reduced PD incidence: cigarette smoking (30-60% risk reduction — complex nicotinic acetylcholine receptor mechanisms); caffeine consumption (dose-dependent inverse association — adenosine A2A receptor antagonism); ibuprofen use; urate levels above median. Age remains the overwhelmingly dominant risk factor — PD prevalence increases from 1% at age 60 to 4-5% above 85 years — reflecting cumulative oxidative stress, impaired protein clearance, and mitochondrial dysfunction in ageing neurons.

Cardinal motor features (TRAP mnemonic): Tremor at rest — the most recognisable feature, present in 70-80% of PD patients; a coarse, rhythmic, 4-6Hz resting tremor typically beginning unilaterally in the hand or fingers ('pill-rolling tremor' — thumb rolling against forefinger as if rolling a pill), suppressed or reduced by intentional movement, worsened by stress or distraction — a key distinction from essential tremor which is action-related and worsened with movement; Rigidity — increased resistance to passive limb movement throughout the full range of motion ('lead-pipe rigidity') or superimposed on tremor giving a 'cogwheel' quality; Akinesia/Bradykinesia — slowness (brady-) and difficulty initiating (akinesia) voluntary movement, with progressive reduction in amplitude of repetitive movements (finger tapping, foot tapping) over time — detected on examination; manifests clinically as micrographia (small cramped handwriting), reduced facial expression (hypomimia or 'masked face'), hypophonia (soft monotone voice), and difficulty with fine motor tasks (buttoning, handling utensils); Postural instability — loss of postural reflexes causing imbalance and falls — a late feature (typically after 5-8 years), absent at diagnosis (its early presence suggests Parkinson-plus syndromes). Non-motor symptoms often precede motor features by 5-20 years in the prodromal phase and are frequently more disabling than motor symptoms in later disease: anosmia or hyposmia (loss of smell — present in 90% of PD, one of the earliest non-motor features); REM sleep behaviour disorder (RBD — acting out vivid dreams, a highly specific early biomarker converting to PD or Lewy body dementia in 80% within 10 years); constipation; depression and anxiety (present in 40-50%); autonomic dysfunction (orthostatic hypotension — lightheadedness on standing, falls; urinary dysfunction — urgency and frequency; sexual dysfunction; hyperhidrosis); and cognitive impairment ranging from mild cognitive impairment to Parkinson's disease dementia.

Parkinson's disease is a clinical diagnosis — there is no single definitive diagnostic test. The UK Parkinson's Disease Society Brain Bank Clinical Diagnostic Criteria require: (1) diagnosis of bradykinesia; (2) at least one of resting tremor, rigidity, or postural instability; (3) exclusion of alternative causes (drug-induced parkinsonism — antipsychotics, metoclopramide; vascular parkinsonism; Wilson's disease; repeated head trauma; encephalitis lethargica; normal pressure hydrocephalus); and (4) at least 3 of 10 supporting criteria including: unilateral onset, rest tremor, progressive and persistent disorder, asymmetric motor signs, excellent response to levodopa (over 70% improvement), and levodopa dyskinesias. Neuroimaging: MRI brain is typically performed at initial diagnosis — normal in idiopathic PD but may show T2/FLAIR signal changes in the substantia nigra in advanced PD; atypical MRI features (superior cerebellar peduncle atrophy in PSP — 'hummingbird sign'; putamen signal change in MSA) suggest Parkinson-plus syndromes with worse prognosis and poor levodopa response. DaTSCAN (DAT-SPECT: dopamine transporter SPECT imaging with ioflupane-123): demonstrates reduced dopamine transporter binding in the striatum (reduced 'comma' to 'full stop' shape in the caudate/putamen) — confirms nigrostriatal degeneration and distinguishes PD from essential tremor (normal DaTSCAN), drug-induced parkinsonism, and psychogenic tremor; recommended when clinical diagnosis is uncertain. Genetic testing: offered to young-onset PD patients (below 50 years), those with a strong family history, or those from at-risk populations (Ashkenazi Jewish heritage — LRRK2 G2019S, GBA). Neuropsychological assessment at baseline and serially for cognitive monitoring.

Levodopa/carbidopa is the most effective dopaminergic therapy and the gold standard for PD motor symptoms: carbidopa inhibits peripheral decarboxylation of levodopa, allowing CNS penetration; controlled-release preparations and intestinal gel (Duodopa/carbidopa-levodopa enteral suspension) address wearing-off and motor fluctuations. Dopamine agonists (pramipexole 0.75-3mg daily; ropinirole 3-24mg daily; rotigotine patch 2-8mg/24h) are first-line in younger patients (below 65) to delay dyskinesias from long-term levodopa; impulse control disorders (gambling, hypersexuality, binge eating) occur in 14-17% and require monitoring and drug reduction. MAO-B inhibitors (rasagiline 1mg daily; selegiline 5-10mg) provide mild motor benefit as monotherapy or adjunct, with potential neuroprotective effects. COMT inhibitors (entacapone 200mg with each levodopa dose; opicapone 50mg once daily) extend levodopa duration by preventing peripheral catechol-O-methyltransferase metabolism — reducing wearing-off fluctuations. Deep Brain Stimulation (DBS): bilateral subthalamic nucleus (STN) or globus pallidus interna (GPi) DBS is a highly effective surgical option for selected patients with motor fluctuations or disabling dyskinesias not controlled by optimal medication and preserved cognition — reduces 'off' time by 50-70% and improves dyskinesias; not indicated for Parkinson-plus syndromes or patients with significant dementia or psychiatric comorbidity. LCIG (levodopa-carbidopa intestinal gel — Duodopa): continuous intestinal infusion via percutaneous gastrojejunostomy reduces motor fluctuations in advanced PD with predictable on-off cycles not controlled by oral optimisation. Amantadine reduces levodopa-induced dyskinesias. Apomorphine (subcutaneous bolus or continuous infusion pump): potent D1/D2 agonist for severe refractory motor fluctuations. Exercise: 150+ minutes per week of moderate aerobic exercise improves motor function and may slow neurodegeneration.

Motor complications of long-term levodopa therapy develop in 50% of patients within 5 years and 80-90% within 10 years: wearing-off (predictable recurrence of motor symptoms in the last hour before the next levodopa dose, managed with dose reduction intervals, extended-release preparations, or COMT inhibitor addition); dyskinesias (involuntary choreiform or dystonic movements at peak levodopa dose — managed with amantadine, dose reduction, or DBS); and unpredictable on-off fluctuations. Parkinson dementia (PDD): affects 80% of patients after 20 years of disease, with 30% developing dementia within 3-5 years of diagnosis; treated with rivastigmine (ChEI — approved for PDD); lewy body dementia (DLB) has earlier dementia onset. Psychosis (visual hallucinations, paranoid delusions) from dopaminergic therapy occurs in 20-40% of patients: requires structured medication review (reduce anticholinergics, then amantadine, then dopamine agonists, then MAO-B inhibitors first before levodopa reduction); antipsychotics quetiapine or clozapine (with white cell monitoring) are the only safe options — all other antipsychotics (including olanzapine) are contraindicated as they worsen parkinsonism severely. Autonomic failure: orthostatic hypotension (treat with increased salt and fluid, compression stockings, midodrine, fludrocortisone); urinary dysfunction (urgency, incontinence — mirabegron or solifenacin); constipation (macrogol, osmotic laxatives); sialorrhoea (sublingual atropine drops, botulinum toxin to parotids). Falls and hip fractures are a leading cause of death and disability in advanced PD. Aspiration pneumonia from progressive dysphagia is the most common immediate cause of death in PD — requires early speech and language therapy and FEES assessment.

No disease-modifying therapy currently proven to slow or halt PD neurodegeneration is clinically available, despite active research in alpha-synuclein immunotherapy (prasinezumab, cinpanemab — currently in Phase II/III trials), GBA enzyme replacement, LRRK2 kinase inhibitors, and mitochondrial pathway interventions. Exercise is the most evidence-based intervention for symptomatic improvement and may have neuroprotective effects: 150 minutes per week of moderate-intensity aerobic exercise (walking, cycling, dancing — Tango and non-contact boxing programmes show specific benefits for PD balance and gait) plus resistance training (twice weekly) and balance/flexibility exercises (Tai Chi significantly reduces falls risk by 47% in PD — a key quality-of-life intervention). Multidisciplinary management is integral throughout the disease course: movement disorder neurologist for medication optimisation; physiotherapist specialised in PD for gait training, fall prevention, and exercise prescription; speech and language therapist for hypophonia (LOUD speech therapy — 70-80% response), dysphagia assessment (FEES or videofluoroscopy), and saliva management; occupational therapist for home adaptations, activities of daily living, and driving assessment; dietitian for weight maintenance, constipation management (adequate fibre and fluid), and dysphagia-appropriate diet; specialist PD nurse as the central coordinator and first contact for medication queries and emerging symptoms. Palliative care integration should be considered in advanced PD — managing non-motor symptoms, caregiver burden, and end-of-life planning. Patient support organisations (Parkinson's UK, EPDA) improve coping, medication adherence, and social connection. Avoidance of medications that can precipitate or worsen parkinsonism: metoclopramide, prochlorperazine, antipsychotics (except quetiapine and clozapine), and first-generation antihistamines.

See a GP urgently for a neurology referral if you notice: a resting tremor (tremor present when the hand is still, disappearing with voluntary movement), slowness of movement (taking longer to start and complete tasks), stiffness or rigidity of limbs, reduced arm swing on one side when walking, or changes in handwriting (micrographia — writing becoming progressively smaller). Early referral to a neurologist (movement disorder specialist) is critical — the earlier treatment starts, the better the functional outcome. See a GP also for non-motor prodromal symptoms that can precede PD by years: loss of smell, REM sleep behaviour disorder (acting out dreams), constipation, and depression. Seek urgent review for: a sudden worsening of motor or non-motor symptoms (possible intercurrent illness, medication issue, or Parkinsonism-hyperpyrexia syndrome from dopaminergic medication withdrawal — which is a medical emergency); new falls, swallowing difficulties, or significant cognitive decline; and acute psychosis (hallucinations, paranoid delusions) from dopaminergic medication — requires prompt specialist review.