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Pernicious anemia is a megaloblastic anemia caused by vitamin B12 deficiency due to autoimmune destruction of gastric parietal cells and intrinsic factor deficiency, leading to impaired absorption of B12 in the ileum.

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It represents the hematological manifestation of autoimmune (Type A) atrophic gastritis.

https://youtu.be/K_QGOao7kMg

https://www.youtube.com/watch?v=TNug0MHdhq0

https://youtu.be/QNfmbiJ_2Ts

Etiopathogenesis

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Loss of intrinsic factor + achlorhydria → defective B12 absorption in terminal ileum → Vitamin B12 deficiency → defective DNA synthesis → Megaloblastic anemia

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Autoimmune mechanism:

• Autoantibodies against parietal cells (H+/K+ ATPase) → parietal cell destruction.
• Autoantibodies against intrinsic factor → block binding of B12 or B12–IF absorption.

Neurological manifestations:

• Demyelination of dorsal columns and lateral corticospinal tracts (subacute combined degeneration).

Risk groups:

• Older adults (>50 years), Northern Europeans
• Patients with other autoimmune diseases (thyroiditis, vitiligo, T1DM).

Pathology

• Bone marrow: megaloblastic erythropoiesis (large erythroid precursors).
• Peripheral smear:
  • Macro-ovalocytes.
  • Hypersegmented neutrophils.