Review Question - QID 217282

This patient who presents with symptoms of anemia (fatigue and pallor), indigestion, and bloating as well as macrocytic erythrocytes in the setting of a diverse diet most likely has pernicious anemia. This disease would present with decreased B12 levels, increased gastrin levels, and increased gastric pH.

Pernicious anemia is an autoimmune disease caused by destruction of gastric parietal cells. These cells normally produce gastric acid as well as intrinsic factor (required for vitamin B12 absorption) so patients can present with symptoms of macrocytic anemia (fatigue, pallor) as well as bloating and loss of appetite. Laboratory tests will show decreased serum B12, increased serum methylmalonic acid, increased serum homocysteine, increased serum gastrin, as well as the presence of anti-intrinsic factor and parietal antibodies. Peripheral blood smear will show hypersegmented neutrophils and megalocytic erythrocytes.

Htut et al. present a review of the pathophysiology and diagnosis of pernicious anemia. They discuss how this disease may mimic other disorders but needs to be recognized in a timely fashion because it can easily be treated with cobalamin repletion.

Figure A is a table presenting sets of laboratory changes including serum gastrin level, serum vitamin B12 level, and gastric pH.

Incorrect Answers:
Answer 1: Decreased B12 levels, increased gastrin levels, and decreased gastric pH may occur in Zollinger-Ellison syndrome where ectopic production of gastrin leads to hypersecretion of gastric acid and gastric mucosal damage.

Answer 3: Decreased B12 levels, normal gastrin levels, and normal gastric pH may occur in cases where patients have a B12 deficient diet. This patient with a varied diet most likely has adequate dietary intake of vitamin B12.

Answer 4: Increased B12 levels, decreased gastrin levels, and increased gastric pH may occur in patients who have a primary decrease in gastrin production by the gastrointestinal system. This is very rare and does not cause megaloblastic anemia.

Answer 5: Increased B12 levels, decreased gastrin levels, and decreased gastric pH may occur in patients who have hyperactive gastric parietal cells since these cells produce both gastric acid as well as intrinsic factor leading to B12 absorption. This is very rare and does not cause megaloblastic anemia.

Bullet Summary:
Pernicious anemia is caused by the autoimmune destruction of parietals leading to decreased serum vitamin B12, increased serum gastrin, and increased gastric pH.