A 62-year-old man from Delhi presents with a 3-year history of progressive tremor in his right hand, which worsens at rest and improves with intentional movement. On examination, he has a resting tremor at 4–5 Hz, mild rigidity in the neck and shoulders, and a slightly slow gait with reduced arm swing on the right. He denies cognitive complaints. His blood pressure is 130/85 mmHg, heart rate 78/min. What is the most likely diagnosis?

## Clinical Diagnosis of Parkinson Disease ### Cardinal Features Present **Key Point:** The diagnosis of Parkinson disease rests on the presence of at least two of the cardinal motor features: resting tremor, rigidity, and bradykinesia. This patient exhibits all three. 1. **Resting tremor** — 4–5 Hz frequency, unilateral, improves with intentional movement (disappears with action) 2. **Rigidity** — neck and shoulder stiffness ("lead pipe" or "cogwheel" pattern) 3. **Bradykinesia** — slow gait with reduced arm swing (a hallmark of hypokinetic movement disorder) ### Distinguishing Features from Alternatives | Feature | Parkinson Disease | Essential Tremor | Cerebellar Tremor | Thyrotoxicosis | |---------|-------------------|------------------|-------------------|----------------| | **Tremor type** | Resting, 4–5 Hz | Postural/kinetic, 8–12 Hz | Intention tremor | Fine, rapid, postural | | **Rigidity** | Present (lead pipe) | Absent | Absent | Absent | | **Bradykinesia** | Present | Absent | Absent | Absent | | **Gait** | Slow, reduced arm swing | Normal | Ataxic | Normal | | **Onset** | Insidious, unilateral | Bilateral, family history | Acute/subacute | Acute systemic symptoms | **Clinical Pearl:** The combination of resting tremor + rigidity + bradykinesia is pathognomonic for Parkinson disease. The unilateral onset and 3-year progressive course fit the typical presentation. ### Diagnostic Criteria (UK Parkinson's Disease Society Brain Bank) **High-Yield:** Diagnosis requires: - Bradykinesia (mandatory) PLUS - At least one of: resting tremor OR rigidity - Absence of atypical features (early dementia, early autonomic failure, early vertical gaze palsy, early cerebellar signs) This patient meets all criteria and has no red flags for atypical parkinsonism. ### Why Other Diagnoses Fail - **Essential tremor:** Postural/kinetic tremor (worsens with action), NO rigidity, NO bradykinesia, often bilateral and familial - **Cerebellar tremor:** Intention tremor (worsens on target approach), ataxic gait, nystagmus, NO rigidity - **Thyrotoxicosis:** Fine rapid tremor, tachycardia, weight loss, warm skin — systemic signs absent here [cite:Harrison 21e Ch 428]