Pernicious anemia is an autoimmune disease that targets gastric parietal cells, resulting in gastritis, vitamin B12 (cyanocobalamin) deficiency, and a megaloblastic anemia. In this condition, autoantibodies also inhibit vitamin B12 absorption. The cause is unknown, and the role of Helicobacter pylori infection in the development of autoimmune gastritis is also unknown. Pernicious anemia most often presents in adults, with an average age of diagnosis between 70 and 80 years old, although there are rare inherited forms that can present in neonates and early childhood. Patients with pernicious anemia are at increased risk for other autoimmune conditions such as autoimmune thyroiditis, vitiligo, and diabetes mellitus type 1. Incidence is increased in people of European and African descent, and females are more frequently affected than males (3:1).

Typical symptoms include malaise, pallor, and dyspnea attributable to anemia. Vitamin B12 deficiency can result in both central and peripheral nervous system manifestations (eg, paresthesias, loss of proprioception, poor concentration, and depression) as well as anosmia and atrophic glossitis. Gastrointestinal symptoms (eg, abdominal pain, diarrhea, and constipation) may be present.

If treated, many of these manifestations are reversible. However, if undiagnosed and untreated, some neurologic manifestations can be permanent. The hallmarks of therapy include vitamin B12 repletion. However, this does not reverse the underlying autoimmune gastritis. If gastrointestinal symptoms develop, patients should be evaluated for gastric cancers given their increased risk.