Question

A 54-year-old man with a history of chronic hyponatremia develops sudden-onset quadriparesis after rapid sodium correction. Which investigation is most appropriate to confirm the diagnosis?

• A. Brainstem evoked potential
• B. Electroencephalogram (EEG)
• C. MRI of the brain
• D. Nerve conduction studies

Hint:

Rapid correction of chronic hyponatremia can cause central pontine myelinolysis; confirm with MRI brain.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The clinical scenario of quadriparesis occurring shortly after the rapid correction of chronic hyponatremia is a classic description of Osmotic Demyelination Syndrome (ODS), formerly known as Central Pontine Myelinolysis (CPM). We need to identify the diagnostic imaging modality.
Step 2: Detailed Explanation:

Pathophysiology of ODS: Chronic hyponatremia leads to an adaptation of brain cells where they lose intracellular osmolytes to prevent swelling. If sodium is corrected too rapidly (> 8-10 mEq/L in 24h), the osmotic pressure shifts water out of the brain cells too quickly, leading to the destruction of myelin sheaths, particularly in the pons.

Clinical Presentation: Symptoms usually appear 2-6 days after the rapid correction. They include dysarthria, dysphagia, and a rapidly progressing quadriparesis (locked-in syndrome).

Diagnostic Imaging: MRI of the brain is the investigation of choice. It characteristically shows symmetric T2-hyperintense and T1-hypointense lesions in the central pons, often with a "trident-shaped" appearance. Importantly, early CT scans may be normal.

MRI Sequences: Diffusion-weighted imaging (DWI) can detect changes within 24 hours of symptom onset, making it more sensitive than conventional T1/T2 sequences in the early phase.

Why not others? EEG (Option B) and Nerve conduction studies (Option D) are irrelevant for a central demyelinating process. Evoked potentials (Option A) might show abnormalities but are not diagnostic or as specific as MRI.

Step 3: Final Answer:
MRI of the brain is the gold-standard investigation to confirm the presence of lesions characteristic of Osmotic Demyelination Syndrome.