Site of lesion: Substantia nigra pars compacta (SNPC)


Dopamine-Acetylcholine balance:


  1. Idiopathic (MC): Known as Parkinson’s disease
  2. Drugs: MC cause of secondary/ acquired parkinsonism; MC drug: Typical antipsychotics (Known as Pseudoparkinsonism).

Clinical features:

  • T: Tremor (Earliest & MC symptom; resting tremor)
  • R: Rigidity (Cog wheel rigidity)
  • A: Akinesia
  • P: Postural instability.

Other important clinical features:

  • Tendency to fall → to prevent this fall, patient tries to run towards the destination → “Festinating gait”
  • Difficulty to stop once walking started → “Kinesia paradoxa”
  • Decreased blinking: Blinking increases on tapping over the forehead region → “Myerson sign”
  • Micrographia (progressively smaller handwriting).



  • The swallow tail sign describes the normal axial imaging appearance of substantia nigra on high resolution MRI
  • Absence of the swallow tail sign in substantia nigra has a high diagnostic accuracy for Parkinsonism.


  • ?123-ioflupane is a radiopharmaceutical for the diagnosis of Parkinson disease
  • Striatal dopaminergic pathway is visualized using SPECT brain imaging
  • Coma shaped uptake is normal.

Treatment (Reference: Harrison 20th Edition):

  • First line drug: Rasagiline
  • Single most effective agent in the treatment of parkinson’s disease: Levodopa
  • DOC in Levodopa induced vomiting: Domperidone (D2 blocker)
  • Peripheral dopa-decarboxylase inhibitor: Carbidopa
  • DOC in “weaning off” (Improvement gained from a dose of Levodopa medication gradually fades off) period: Entacapone (COMT inhibitor)
  • Entacapone increases the bioavailability of Levodopa in patient with parkinsonism
  • Tolcapone is toxic to liver, causes liver failure; hence discontinued
  • DOC to overcome “on & off” phenomenon [On= Dyskinesia, Off= Hypokinesia]/ Rescue therapy: Apomorphine (D4 agonist, administered subcutaneously)
  • Amantadine is the only drug that has been demonstrated to treat dyskinesia without worsening parkinsonism
  • Amantadine has mixed mechanisms of action:
    1. Dopaminergic agonist
    2. Anticholinergic
    3. NMDA antagonism
  • DOC of drug induced parkinsonism: Trihexiphenydil.


Parkinson plus syndromes

They are a group of neurodegenerative diseases featuring the classical features of Parkinson’s disease with additional features that distinguish them from idiopathic Parkinson’s disease.

Progressive supranuclear palsy (PSP):

  • PD with absent tremors + Dementia
  • CT: Midbrain atrophy (Hummingbird sign).

Multisystem atrophy (MSA):

  • Parkinsonism + Autonomic instability
  • CT: Hot cross bun pons.

Wheelchair sign of Quinn: It is a red flag (bad prognostic) sign of Parkinsonism because patients with parkinson plus syndrome become wheel chair bound much earlier in the course of the illness than those with idiopathic Parkinson’s disease.

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