Pernicious Anemia
Caused by autoimmune destruction of parietal cells in the stomach. This leads to decreased Intrinsic factor → ↓ B12 absorption in terminal ileum.
- Associated with autoimmune gastritis & other autoimmune diseases (e.g., thyroiditis, vitiligo)
Clinical Features
- Macrocytic anemia (MCV >100)
- Loss of B12
- Neurologic symptoms (specific to B12 deficiency):
- Peripheral neuropathy
- Dorsal column dysfunction (↓ vibration, proprioception)
- Subacute combined degeneration (posterior & lateral columns)
- Ataxia, spasticity, dementia
- Glossitis, fatigue, pallor
- Increased risk of gastric cancer (adenocarcinoma)
Diagnosis
- ↓ Serum B12
- ↑ MCV
- ↑ Methylmalonic acid and ↑ homocysteine (specific for B12)
- Positive anti-intrinsic factor antibodies (most specific test)
- Positive anti-parietal cell antibodies
- Schilling test (rarely used now; tests for intrinsic factor deficiency)
B12 deficiency → neurologic + macrocytic
Folate deficiency → macrocytic without neuro symptoms
Treatment
- IM vitamin B12 injections (initially daily, then monthly)
- Oral B12 can be used if no severe neuro symptoms and compliance is good
- Monitor reticulocyte count: should ↑ within 1 week of treatment
- Neurologic recovery may take months (may not fully resolve if severe)
Complications
- Increased gastric cancer risk
- Irreversible neurologic damage if untreated
- Associated with other autoimmune diseases (screen if needed)
Classic Vignette
- Elderly woman with fatigue, numbness, ataxia, glossitis
- Labs: ↑ MCV, ↓ B12, positive anti-IF Abs
- Coexisting hypothyroidism, vitiligo, or T1DM