A 52-year-old Indian woman presents with progressive fatigue, paresthesias in both feet, and glossitis. On examination, she has pallor and a positive Romberg sign. Her CBC shows Hb 7.2 g/dL with MCV 118 fL. Peripheral blood smear reveals hypersegmented neutrophils and macro-ovalocytes. Serum B12 is 180 pg/mL (normal 200). What is the most appropriate next step in management?

Question

A 52-year-old Indian woman presents with progressive fatigue, paresthesias in both feet, and glossitis. On examination, she has pallor and a positive Romberg sign. Her CBC shows Hb 7.2 g/dL with MCV 118 fL. Peripheral blood smear reveals hypersegmented neutrophils and macro-ovalocytes. Serum B12 is 180 pg/mL (normal >200). What is the most appropriate next step in management?

Accepted Answer

A. Initiate parenteral cyanocobalamin 1000 mcg weekly and investigate the cause of B12 deficiency. ## Clinical Context
This patient presents with **megaloblastic anemia** with neurological manifestations (paresthesias, positive Romberg sign) consistent with **B12 deficiency with subacute combined degeneration (SCD)**. The low serum B12 (180 pg/mL) and characteristic blood findings confirm the diagnosis.

## Why Parenteral B12 is Essential

**Key Point:** Neurological complications of B12 deficiency require **immediate parenteral replacement** — oral therapy is insufficient because:
  - Neurological damage can be **irreversible** if delayed
  - Parenteral route bypasses intestinal absorption defects (suspected pernicious anemia given glossitis and positive Romberg)
  - Parenteral B12 achieves rapid, high-dose tissue saturation

## Investigation Strategy

**High-Yield:** Once B12 replacement is initiated, investigation for the **cause** (parietal cell antibodies, intrinsic factor antibodies, Schilling test if available) should proceed in parallel:
  - Suspected pernicious anemia (autoimmune gastritis) is the most common cause in this age group
  - Identifying the etiology guides long-term management (lifelong B12 supplementation)

**Clinical Pearl:** Neurological signs (paresthesias, ataxia, positive Romberg) indicate **urgent need for treatment** — do not delay with additional confirmatory testing before starting parenteral B12.

## Why Not the Other Options?

| Option | Reason |
| --- | --- |
| Oral cyanocobalamin | Ineffective in pernicious anemia (intrinsic factor deficiency); neurological complications demand parenteral route |
| Antibody testing first | Diagnostic confirmation should not delay treatment in a symptomatic patient with neurological signs |
| Metabolite levels before treatment | Methylmalonic acid and homocysteine are elevated in B12 deficiency but are **confirmatory, not therapeutic**; starting treatment immediately is the priority |

[cite:Harrison 21e Ch 102]

Answer

B. Start oral cyanocobalamin 1000 mcg daily and reassess in 2 weeks

Answer

C. Measure serum methylmalonic acid and homocysteine levels before starting any treatment

Answer

D. Perform intrinsic factor antibody and parietal cell antibody testing to confirm pernicious anemia

Explanation

Clinical Context

Why Parenteral B12 is Essential

Investigation Strategy

Why Not the Other Options?

Practice similar questions

Join our NEET PG community

Option	Reason
Oral cyanocobalamin	Ineffective in pernicious anemia (intrinsic factor deficiency); neurological complications demand parenteral route
Antibody testing first	Diagnostic confirmation should not delay treatment in a symptomatic patient with neurological signs
Metabolite levels before treatment	Methylmalonic acid and homocysteine are elevated in B12 deficiency but are confirmatory, not therapeutic; starting treatment immediately is the priority