A 38-year-old chronic alcoholic man presents with macrocytic anaemia, glossitis, and diarrhoea. Which vitamin deficiency best explains his presentation, and what is the key discriminating feature that distinguishes it from thiamine deficiency?

Explanation

## Distinguishing Folate from B12 and Thiamine Deficiency in Alcoholism ### Clinical Presentation Analysis The patient presents with: - **Macrocytic anaemia** (suggests B12 or folate deficiency) - **Glossitis** (suggests B12 or folate deficiency) - **Diarrhoea** (suggests folate or B12 deficiency) - **No mention of neurological symptoms** (ataxia, paresthesia, Wernicke encephalopathy) ### B12 vs. Folate vs. Thiamine: Key Discriminators | Feature | B12 Deficiency | Folate Deficiency | Thiamine Deficiency | |---------|----------------|-------------------|---------------------| | **Macrocytic anaemia** | Yes (megaloblastic) | Yes (megaloblastic) | No | | **Neurological symptoms** | Yes (paresthesia, ataxia, subacute combined degeneration) | **No** | Yes (Wernicke, neuropathy) | | **Glossitis** | Yes | Yes | Minimal | | **Diarrhoea** | Yes | Yes | No | | **Dermatitis** | No | No | Rare | | **Distinguishing feature** | Neurological involvement (paresthesia, ataxia) | **Absence of neurological symptoms** | Wernicke encephalopathy, beriberi | **Key Point:** The **absence of neurological symptoms** (paresthesia, ataxia, Wernicke encephalopathy) in the presence of macrocytic anaemia, glossitis, and diarrhoea is the hallmark of **folate deficiency**, not B12 deficiency. **High-Yield:** Folate deficiency causes **haematological manifestations only** (macrocytic anaemia, glossitis, diarrhoea), while B12 deficiency causes **both haematological AND neurological manifestations** (subacute combined degeneration, paresthesia, ataxia). Thiamine deficiency causes **neurological manifestations** (Wernicke, Korsakoff, beriberi) without anaemia. **Clinical Pearl:** In chronic alcoholics, **folate deficiency is more common than B12 deficiency** because alcohol impairs folate absorption and metabolism. The absence of neurological symptoms helps exclude B12 deficiency and Wernicke encephalopathy (thiamine deficiency). **Mnemonic:** **B12 = Neuro** (B12 deficiency → neurological symptoms: paresthesia, ataxia, subacute combined degeneration). **Folate = Haem only** (Folate deficiency → haematological symptoms only: anaemia, glossitis, diarrhoea, NO neuro). **Thiamine = Wernicke** (Thiamine deficiency → Wernicke encephalopathy, beriberi neuropathy).