A 42-year-old woman from rural Maharashtra presents with progressive fatigue, dyspnea on exertion, and palpitations over 6 months. On examination, she has pallor, glossitis, and a stocking-glove paresthesia. Her hemoglobin is 7.2 g/dL with MCV 78 fL. Peripheral blood smear shows hypochromic microcytic RBCs with occasional target cells. Serum vitamin B12 is 180 pg/mL (normal >200), and serum folate is 2.1 ng/mL (normal >5.4). Iron studies are normal. What is the most likely diagnosis?

Explanation

## Clinical Presentation Analysis This patient presents with a constellation of findings pointing to **combined B12 and folate deficiency**: ### Key Clinical Features **Neurological signs:** - Glossitis (inflamed tongue) - Stocking-glove paresthesia (peripheral neuropathy) - These are hallmarks of B12 deficiency; folate deficiency does NOT cause neurological manifestations **Hematologic findings:** - Microcytic anemia (MCV 78 fL) - Hypochromic RBCs - Normal iron studies (rules out iron deficiency as primary cause) **Laboratory confirmation:** - Both B12 (180 pg/mL) and folate (2.1 ng/mL) are LOW - The combination explains both the neurological AND hematologic picture ### Why Combined Deficiency? In India, **nutritional deficiencies** are common in rural populations due to: - Vegetarian diet (low B12 sources) - Poor folate intake (leafy greens, legumes) - Malabsorption (chronic diarrhea, celiac disease) - Alcohol use disorder **High-Yield:** When you see BOTH neurological signs (paresthesia, glossitis) AND microcytic anemia with LOW B12 and LOW folate, the answer is combined deficiency. ### Differential Diagnosis Table | Feature | B12 Deficiency | Folate Deficiency | Iron Deficiency | Combined B12+Folate | |---------|---|---|---|---| | Neurological signs | Yes | **No** | No | Yes | | Glossitis | Yes | Yes | No | Yes | | MCV | Macro | Macro | Micro | Micro* | | B12 level | Low | Normal | Normal | Low | | Folate level | Normal | Low | Normal | Low | | Iron studies | Normal | Normal | Abnormal | Normal | *In combined deficiency, iron depletion can lower MCV despite B12/folate deficiency. **Key Point:** The presence of neurological manifestations (paresthesia, glossitis) is the clinching finding that distinguishes this from isolated folate deficiency, which causes only hematologic changes. **Clinical Pearl:** In India, combined nutritional deficiencies are more common than isolated deficiencies in rural populations. Always check both B12 and folate when one is low.