A 42-year-old male with chronic alcoholism presents with acute onset confusion, ophthalmoplegia (especially medial rectus palsy), and ataxia. He is also found to have nystagmus and confabulation. Which investigation would be most appropriate to confirm the suspected diagnosis before starting treatment?

Explanation

## Clinical Presentation: Wernicke-Korsakoff Syndrome The triad of: 1. **Ophthalmoplegia** (especially medial rectus — CN III palsy) 2. **Ataxia** (gait disturbance) 3. **Confusion/Altered mental status** (with confabulation) ...in a chronic alcoholic is **pathognomonic for Wernicke encephalopathy**, a medical emergency caused by **thiamine (vitamin B1) deficiency**. ## Why ETK Activation Coefficient is Gold Standard **Key Point:** Erythrocyte transketolase (ETK) is a thiamine-dependent enzyme. The **ETK activation coefficient** (ratio of ETK activity with added thiamine pyrophosphate to baseline ETK) is the **most specific functional test** for thiamine deficiency. | Investigation | What It Measures | Specificity | Timing Issues | |---|---|---|---| | **Serum thiamine** | Free thiamine concentration | Moderate | Fluctuates rapidly; can be normal early in deficiency | | **ETK activity + activation coefficient** | **Functional thiamine status** | **Very High** | Reflects tissue thiamine stores; gold standard | | **Plasma pyruvate/lactate** | Indirect metabolic marker | Low | Elevated in many conditions; non-specific | | **MRI brain** | Structural changes | Moderate | Confirms diagnosis retrospectively; not used for acute confirmation | **High-Yield:** Transketolase is a pentose phosphate pathway enzyme that requires thiamine pyrophosphate (TPP) as a cofactor. When thiamine is deficient: - Basal ETK activity is LOW (enzyme cannot function) - Adding exogenous TPP **restores activity** → large activation coefficient (>25% increase is diagnostic) - This is the **functional gold standard** for confirming thiamine deficiency **Mnemonic:** **ABCD of Wernicke** — Ataxia, ophthalmoplegia (eye signs), Confusion, Deficiency (thiamine) ## Why ETK Over Serum Thiamine? **Clinical Pearl:** Serum thiamine levels can be **falsely normal** in early thiamine deficiency because: - The body has limited thiamine stores - Serum levels do not always reflect tissue stores - ETK activation coefficient is a **functional assay** that directly measures the impact of deficiency on enzyme activity **Warning:** Do NOT wait for serum thiamine results before treating. Wernicke encephalopathy is a **medical emergency**. If clinical suspicion is high, start thiamine immediately (100 mg IV daily for 3–5 days) while awaiting ETK results. Delayed treatment risks permanent neurological damage and progression to Korsakoff syndrome (irreversible memory loss).