Parkinson disease

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Parkinson disease



Parkinson disease


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USMLE® Step 1 questions

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Parkinson disease

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USMLE® Step 1 style questions USMLE

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A 70-year-old man with a history of Parkinson disease comes to the office for follow-up. He was diagnosed 6 years ago, and since then, the condition has been well-controlled with levodopa/carbidopa. However, for the past 2 months, the patient reports increased difficulty ambulating, loss of balance and increased rigidity. He is compliant with the treatment and describes fluctuations in the symptoms that improve after he takes the medication. Physical examination reveals diffuse cogwheel rigidity and difficulty walking. A decision is made to add a medication that will descrease the symptoms between levodopa/carbidopa doses. Which of the following best describes the mechanism of action of this medication?  

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Akinesia in Parkinson disease p. 719

Antimuscarinic drugs

Parkinson disease p. 568

Antipsychotic drugs p. 597

Parkinson-like syndrome p. 252

Dopamine p. 243, 334

Parkinson disease p. 568

Gait disturbance

Parkinson disease p. 539

Gait disturbances

Parkinson disease p. 719

MAO inhibitors p. 599

Parkinson disease p. 568

Metoclopramide p. 409

Parkinson-like syndrome p. 252

Muscarinic antagonists p. 242, 712

Parkinson disease p. 568


Parkinson disease drugs p. 569

Neurons p. 507

Parkinson disease p. 568

Parkinson disease p. 538

basal ganglia lesions p. 528

benztropine for p. 242

dopaminergic pathways p. 514

drug therapy for p. 568

Lewy bodies p. 538

neurotransmitters for p. 512

nigrostriatal pathway and p. 514

presentation p. 719

proteasome and p. 46

resting tremor in p. 537

seborrheic dermatitis association p. 488

trihexyphenidyl p. 242

Parkinson-like syndrome p. 252


Parkinson-like syndrome p. 252

Rigidity in Parkinson disease p. 719

Substantia nigra

Parkinson disease p. 719


Parkinson’s disease, which is sometimes called Parkinson diseaseParkinson’s, or PD, is a movement disorder where the dopamine-producing neurons in the substantia nigra of the brain undergo degeneration.

Parkinson’s is one of the most common neurological disorders. It’s a progressive, adult-onset disease, and it gets more common with age. Most of the time, there’s no known cause. But in a few cases, there might be a genetic cause, like mutations in the PINK1, parkin, or alpha synuclein genes, and in rare cases, Parkinsonian symptoms may be caused by MPTP, a toxic impurity that can be found in the recreational drug MPPP or desmethylprodine, which is a synthetic opioid.

In other people, one or more risk factors, rather than a single outright cause, might contribute to Parkinson’s, for example pesticide exposure or DNA variants in genes like LRRK2.

No matter what the cause is, Parkinson’s derives from the death of dopamine-producing, or dopaminergic, neurons in the substantia nigra. The name substantia nigra means “black substance,” since it is darker than other brain regions when you look at a slice of the brain on an autopsy.

We usually refer to the substantia nigra as if it’s in a single location, but there are actually two of these regions in the brain, one on each side of the midbrain. The substantia nigra is a part of the basal ganglia, a collection of brain regions that control movement through their connections with the motor cortex.

In Parkinson’s, these darkened areas of substantia nigra gradually disappear. Under a microscope, Lewy bodies, which are eosinophilic, round inclusions made of alpha-synuclein protein are present in the affected substantia nigra neurons before they die. The function of alpha-synuclein is unknown, as well as the significance of Lewy bodies, and they are both found in other diseases like Lewy body dementia and multiple system atrophy.


Parkinson's is a progressive movement disorder caused by degeneration of dopamine-producing neurons in the substantia nigra, specifically in the pars compacta, which leads to resting tremor, rigidity, problems initiating movement, and postural instability, and for which therapy primarily focuses on increasing brain dopamine.

There is no cure for this condition, but medications can increase dopamine levels in the brain and control tremors. There is also deep-brain stimulation, which involves an implantable device that directly sends electrical signals to the basal ganglia that counteract the abnormal signaling in Parkinson's.


  1. "Robbins Basic Pathology" Elsevier (2017)
  2. "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
  3. "Pathophysiology of Disease: An Introduction to Clinical Medicine 7/E (ENHANCED EBOOK)" McGraw Hill Professional (2014)
  4. "CURRENT Medical Diagnosis and Treatment 2020" McGraw Hill Professional (2019)
  5. "Parkinson's disease" The Lancet (2015)
  6. "Parkinson's disease" The Lancet (2004)

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