A 45-year-old man complains of recurrent nausea and abdominal distress. A gastric biopsy shows atrophy of the mucosa in the fundus and body, with marked lymphocytic infiltration. Blood studies show severe macrocytic anemia with a mean corpuscular volume of 110 mm3. In addition, numerous hypersegmented neutrophils are appreciated on a blood smear. Which of the following is the MOST likely pathogenetic mechanism of this patient's anemia?
Autoimmune gastritis is characterized by atrophy and chronic inflammation of mucosa of the fundus and body of the stomach. This form of gastritis is due to an autoimmune response mediated by autoantibodies against intrinsic factor (IF). Most such autoantibodies block binding of vitamin B12 to IF ("blocking" antibodies), thus preventing absorption of vitamin B12. The resultant picture is megaloblastic anemia, with abnormally large (macrocytic) erythrocytes and hypersegmented neutrophils.Also know:Chronic blood loss and deficient iron absorption cause iron deficiency anemia, with the former being the most common etiology in industrialized countries. Iron deficiency anemia is characterized by small (microcytic) erythrocytes (mean corpuscular volume < 80 mm3). H. pylori infection is an impoant pathogenetic factor in chronic gastritis affecting the antral mucosa in isolation, or in association with involvement of the body of the stomach. Chronic inflammation with lymphocytic infiltration of the mucosa is found on biopsy, and H. pylori can be demonstrated by appropriate silver staining. H. pylori-associated chronic gastritis is usually asymptomatic or manifests with mild and nonspecific upper abdominal discomfo. There is a strong association between H. pylori infection and peptic ulcer disease. H. pylori is also suspected to play an etiologic role in gastric lymphoma and carcinoma. Ref: Mills J.C., Stappenbeck T.S., Bunnett N. (2010). Chapter 13. Gastrointestinal Disease. In S.J. McPhee, G.D. Hammer (Eds),Pathophysiology of Disease, 6e
Autoantibodies to intrinsic factor
Chronic blood loss
Deficient iron absorption
Helicobacter pylori infection