## Investigation of Choice for Progressive Dementia **Key Point:** MRI brain with contrast is the gold standard investigation for suspected dementia to identify structural causes, exclude reversible pathology (normal pressure hydrocephalus, subdural hematoma, space-occupying lesions), and help differentiate between types of dementia (Alzheimer's atrophy pattern vs. vascular dementia). ### Why MRI is Preferred | Feature | MRI | CT | |---------|-----|----| | **Sensitivity for atrophy** | Excellent | Moderate | | **White matter changes** | Detects clearly | May miss subtle changes | | **Reversible causes** | Detects NPH, SDH, tumors | Detects NPH, SDH, tumors | | **Radiation exposure** | None | Present | | **First-line imaging** | Yes (dementia workup) | Alternative if MRI contraindicated | **High-Yield:** In a patient with insidious onset, progressive cognitive decline over years, and stable mental status, the clinical picture is consistent with dementia (not delirium). MRI is essential to: - Rule out reversible causes (NPH, chronic SDH, brain tumors) - Identify patterns suggestive of Alzheimer's disease (medial temporal lobe atrophy) - Exclude vascular dementia (multiple infarcts) **Clinical Pearl:** The 3-year progressive course with stable mental status rules out delirium (acute, fluctuating). The absence of focal neurological signs makes acute stroke unlikely, but imaging is still mandatory to exclude silent infarcts or other structural lesions. ### Role of Other Investigations - **EEG:** Used in delirium (diffuse slowing) or suspected seizures, not routine dementia workup - **Lumbar puncture:** Reserved for suspected CNS infection (meningitis, encephalitis) or normal pressure hydrocephalus if clinical suspicion is high; not first-line - **Serum ammonia/LFTs:** Indicated only if hepatic encephalopathy is suspected; not relevant here [cite:Harrison 21e Ch 297]
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