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Neurology

Parkinson Disease

Progressive neurodegenerative disorder from loss of nigrostriatal dopaminergic neurons causing bradykinesia, rigidity, resting tremor and postural instability.

Last reviewed 7 May 2026 - MedicoMedics editorial team

Dopaminergic neuron loss in substantia nigra

Pathophysiology

Alpha-synuclein Lewy bodies accumulate in substantia nigra pars compacta; motor symptoms after >=60% dopamine loss. Genes: SNCA, LRRK2, GBA.

Sources: MDS Criteria (Mov Disord 2015;30:1591); AAN 2021 Levodopa

Presentation

TRAP: Tremor (4-6 Hz resting), Rigidity (cogwheel), Akinesia/bradykinesia, Postural instability. Non-motor: hyposmia, REM sleep behaviour disorder, constipation.

Diagnosis

Clinical MDS criteria; response to levodopa is supportive. DaT-SPECT differentiates from essential tremor when unclear.

Management

Levodopa/carbidopa (gold standard), dopamine agonists (pramipexole, ropinirole), MAO-B inhibitors (rasagiline). DBS of STN or GPi for motor fluctuations. Pimavanserin for PD psychosis - avoid haloperidol.

Sample USMLE-style MCQs

Try 5 questions on this topic. Practice hundreds more free with a trial.

Question 1

A 68-year-old man has pill-rolling tremor, cogwheel rigidity and micrographia. Which finding supports PD over essential tremor?

Question 2

First-line motor therapy in elderly?

Question 3

Best antipsychotic in PD psychosis?

Question 4

Pathological hallmark of PD?

Question 5

Which DBS target treats dyskinesia?

References

Primary guidelines and peer-reviewed sources used for this entry. Reviewed 7 May 2026 by MedicoMedics editorial team.

  1. MDS Criteria (Mov Disord 2015;30:1591)
  2. AAN 2021 Levodopa

Frequently asked

First clinical sign?

Asymmetric resting tremor and unilateral bradykinesia.

Why avoid haloperidol?

D2 blockade worsens parkinsonism - use pimavanserin or quetiapine.

What is 'wearing off'?

Return of symptoms before next levodopa dose; manage with COMT or MAO-B inhibitors.

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