## Diagnostic Approach to Parkinsonism **Key Point:** MRI brain with T2-weighted and susceptibility-weighted (SWI) sequences is the investigation of choice to exclude secondary causes of parkinsonism before confirming idiopathic Parkinson's disease (PD). ### Why MRI is the First-Line Imaging Investigation 1. **Exclusion of secondary causes:** - Detects structural lesions (tumours, stroke, hydrocephalus) - Identifies iron deposition patterns in atypical parkinsonian syndromes (MSA, PSP, CBD) - SWI sequences show characteristic iron deposition in substantia nigra (normal in PD) vs. putamen (abnormal in MSA) 2. **No radiation exposure** — safer than PET for initial screening 3. **High sensitivity for mimics:** - Normal pressure hydrocephalus (dilated ventricles, periventricular signal change) - Vascular parkinsonism (ischaemic changes) - Neurofibrillary tangles in atypical presentations ### Role of Other Investigations | Investigation | Indication | Limitation | |---|---|---| | **Serum ceruloplasmin & urinary copper** | Wilson's disease screening (young-onset parkinsonism <40 yr) | Not routine for typical late-onset PD | | **Fluorodopa PET** | Research/specialist centres; confirms nigrostriatal dopamine loss | Expensive, not widely available, not first-line | | **EEG** | Seizure disorders, encephalopathy | No role in PD diagnosis | **High-Yield:** MRI is the gatekeeper investigation — it rules out structural mimics and atypical syndromes before committing to long-term dopaminergic therapy. **Clinical Pearl:** In a 62-year-old with classic rest tremor, rigidity, and bradykinesia, MRI is essential to exclude normal-pressure hydrocephalus (which is reversible) and vascular parkinsonism (which requires different management).
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