USMLE Step 2 CK: Neurology – Movement Disorders – Parkinson, Essential Tremor, Drug-induced Parkinsonism

What This Is and Why It Matters for USMLE

Movement disorders, including Parkinson's disease, essential tremor, and drug-induced parkinsonism, are high-yield for Step 1 and Step 2 CK. These conditions are frequently tested in clinical vignettes, requiring students to apply their knowledge of pathophysiology, pharmacology, and clinical presentation.

High-Yield Facts (What You Must Memorize)

• Parkinson's disease: idiopathic, degenerative disorder with dopamine deficiency in the substantia nigra.
• Essential tremor: most common movement disorder, often familial, with action tremor.
• Drug-induced parkinsonism: caused by antipsychotic medications, such as haloperidol.
• Classic presentation:
  • Parkinson's: resting tremor, bradykinesia, rigidity.
  • Essential tremor: action tremor, often in the hands.
• Diagnostic approach:
  • Labs: normal, except for dopamine transporter imaging in Parkinson's.
  • Imaging: normal, except for atrophy in Parkinson's.
• First-line treatment and management:
  • Parkinson's: levodopa with carbidopa.
  • Essential tremor: propranolol or primidone.
  • Drug-induced parkinsonism: discontinue offending medication.

Clinical Pearls & Buzzwords

• Dopamine deficiency-Parkinson's disease.
• Action tremor-essential tremor.
• Antipsychotic medications-drug-induced parkinsonism.
• Dopamine transporter imaging-Parkinson's disease diagnosis.

Step-by-Step Clinical Reasoning

1. Identify the syndrome or presentation: resting tremor or action tremor.
2. Generate a differential: Parkinson's disease, essential tremor, drug-induced parkinsonism.
3. Order appropriate initial tests: lab work (normal) and imaging (normal).
4. Interpret results: atrophy in Parkinson's, normal in essential tremor.
5. Initiate treatment and monitoring: levodopa with carbidopa for Parkinson's, propranolol or primidone for essential tremor.

Common Mistakes & Exam Traps

• The mistake: Failing to consider drug-induced parkinsonism in a patient on antipsychotic medications.
• Why it happens: Misunderstanding the pathophysiology of parkinsonism.
• How to avoid it: Always consider the patient's medication list when evaluating a movement disorder.

• Exam board insight: The examiners often test this knowledge in a clinical vignette with a patient on antipsychotic medications.

• The mistake: Not ordering dopamine transporter imaging in a patient with suspected Parkinson's disease.

• Why it happens: Rushing through the exam and not considering the diagnostic approach.
• How to avoid it: Take your time and consider the diagnostic approach for each patient.
• Exam board insight: The examiners often test this knowledge in a clinical vignette with a patient suspected of having Parkinson's disease.

How It’s Tested on USMLE

• Step 1: Basic science vignette, such as a molecular mechanism or pathology slide, testing knowledge of dopamine deficiency and parkinsonism.
• Step 2 CK: Clinical vignette, such as a patient with a resting tremor, testing knowledge of diagnosis and next step in management.
• Step 3: Similar to Step 2 CK, plus prognosis, risk factors, and CCS management, such as ordering dopamine transporter imaging.

CCS (Step 3) Relevance (If Applicable)

• Initial orders: lab work (normal) and imaging (normal).
• Monitoring and follow-up: levodopa with carbidopa for Parkinson's, propranolol or primidone for essential tremor.
• Common mistakes: not ordering dopamine transporter imaging in a patient with suspected Parkinson's disease.

Practice Questions (3-5 single-best-answer)

Question 1: A 65-year-old man presents with a resting tremor and bradykinesia. Which of the following is the most likely diagnosis? A) Essential tremor B) Parkinson's disease C) Drug-induced parkinsonism D) Multiple system atrophy

Answer: B) Parkinson's disease

Explanation: The patient's resting tremor and bradykinesia are classic symptoms of Parkinson's disease.

Question 2: A 40-year-old woman presents with an action tremor in her hands. Which of the following is the most likely diagnosis? A) Parkinson's disease B) Essential tremor C) Drug-induced parkinsonism D) Multiple system atrophy

Answer: B) Essential tremor

Explanation: The patient's action tremor in her hands is classic for essential tremor.

Question 3: A 50-year-old man presents with a history of schizophrenia and is taking haloperidol. He now presents with a resting tremor and bradykinesia. Which of the following is the most likely diagnosis? A) Parkinson's disease B) Essential tremor C) Drug-induced parkinsonism D) Multiple system atrophy

Answer: C) Drug-induced parkinsonism

Explanation: The patient's history of schizophrenia and use of haloperidol make drug-induced parkinsonism the most likely diagnosis.

Quick Reference Card (60-Second Summary)

• Dopamine deficiency-Parkinson's disease.
• Action tremor-essential tremor.
• Antipsychotic medications-drug-induced parkinsonism.
• Dopamine transporter imaging-Parkinson's disease diagnosis.
• Levodopa with carbidopa-Parkinson's disease treatment.
• Propranolol or primidone-essential tremor treatment.
• Discontinue offending medication-drug-induced parkinsonism treatment.

If You Get Stuck on Test Day

• Eliminate obviously wrong answers: if a patient is taking antipsychotic medications, consider drug-induced parkinsonism.
• Use the "next best step" hierarchy: always consider the patient's medication list when evaluating a movement disorder.
• For Step 3 CCS: order lab work (normal) and imaging (normal) in a patient with suspected Parkinson's disease.

Related USMLE Topics

• Dystonia: a movement disorder with involuntary muscle contractions, often caused by tardive dyskinesia.
• Chorea: a movement disorder with irregular, unpredictable movements, often caused by Huntington's disease.
• Myoclonus: a movement disorder with sudden, brief muscle contractions, often caused by epilepsy.