AKT · Neurology/Movement & neurodegeneration

Parkinson disease

Loss of substantia nigra dopaminergic neurons (Lewy bodies, α-synuclein)

Overview

A progressive neurodegenerative disorder from dopaminergic neuron loss in the substantia nigra, defined by the motor triad of bradykinesia, rigidity and a resting tremor, classically ASYMMETRIC. The exam tests distinguishing it from essential tremor, drug-induced parkinsonism and the Parkinson-plus syndromes.

Recognise

Bradykinesia + cogwheel rigidity + a 4–6 Hz "pill-rolling" RESTING tremor (asymmetric onset)
Postural instability, shuffling festinant gait, reduced arm swing, hypomimia, micrographia
Non-motor: anosmia, REM sleep behaviour disorder, constipation, depression, later cognitive decline

Red flags

Early falls/postural instability, vertical gaze palsy, early autonomic failure, or symmetry/poor levodopa response → a Parkinson-PLUS syndrome

Differentials & how to tell them apart

Essential tremorsymmetric ACTION/postural tremor, improves with alcohol, no bradykinesia/rigidity

Drug-induced parkinsonismsymmetric, on dopamine antagonists (antipsychotics, metoclopramide) — reversible

Progressive supranuclear palsyearly falls + vertical gaze palsy

Multiple system atrophyearly autonomic failure + cerebellar signs, poor levodopa response

Lewy body dementiadementia within 1 year of parkinsonism + visual hallucinations

Investigations

Clinical diagnosis. DaTscan only if uncertain (e.g. vs essential tremor); brain imaging to exclude structural/vascular causes.

Management

Levodopa (with a decarboxylase inhibitor) when motor symptoms affect quality of life

1Refer to a specialist. If motor symptoms affect quality of life → levodopa (most effective); if not yet → dopamine agonist or MAO-B inhibitor.Gate: NEVER stop levodopa abruptly (risk of akinetic crisis / neuroleptic-malignant-like state); if a patient cannot take oral medication, use a dopamine-agonist patch (rotigotine) as rescue
2Manage motor complications (dyskinesia, on-off), non-motor symptoms (depression, REM sleep behaviour, constipation), and avoid dopamine-blocking antiemetics/antipsychotics (use domperidone/quetiapine).

Levodopa (+ carbidopa/benserazide) — most effective for motor symptoms affecting QoL; long-term dyskinesias/on-off

Dopamine agonists (ropinirole, pramipexole) — impulse-control disorders; younger patients

MAO-B inhibitors (selegiline, rasagiline) — early/adjunct

Key points

Asymmetric resting tremor + bradykinesia = Parkinson disease; symmetric action tremor improving with alcohol = essential tremor. Avoid metoclopramide/typical antipsychotics (worsen it). Red-flag features point to Parkinson-plus.

Monitor & prognosis

Motor/non-motor symptoms, levodopa complications, falls, cognition.

Progressive; good symptomatic response to levodopa for years.

Source: NICE NG71 (Parkinson disease)