Review Question - QID 104357

This patient is presenting with anemia, falls (neurologic dysfunction), and an elevated methylmalonic acid (MMA) level suggesting a diagnosis of vitamin B12 deficiency.

Macrocytic anemia is an anemia in which the erythrocytes are too large with a MCV > 100 fL. Some common causes of macrocytic anemia include: vitamin B12/folate deficiencies, liver disease, chronic alcoholism, hypothyroidism, and certain drugs (such as sulfa drugs). Of these causes, only vitamin B12 and folate deficiencies would result in hypersegmented neutrophils on peripheral blood smear. Vitamin B12 and folate deficiencies can be differentiated by checking homocysteine and methylmalonic acid levels. Homocysteine is increased in both B12 and folate deficiencies. Methylmalonic acid is increased in B12 deficiency but is normal in folate deficiency. Neurologic symptoms are also unique to vitamin B12 deficiency and may present with dorsal column dysfunction including symptoms such as ataxia and decreased proprioception/vibration sensation.

Incorrect Answers:
Answer 1: Alcohol use may cause a megaloblastic anemia (both primarily and secondary to folate depletion due to poor nutrition habits); however, neurologic symptoms and the MMA level would likely be normal in this condition.

Answer 2: Folate deficiency is common in alcoholics and presents with a megaloblastic anemia without neurologic symptoms or an elevated MMA level.

Answer 3: Hypothyroidism can present with a megaloblastic anemia, fatigue, weight gain, hyponatremia, and bradycardia.

Answer 4: Iron deficiency presents with a microcytic anemia secondary to bleeding or poor dietary habits.

Bullet Summary:
Vitamin B12 deficiency can present with a megaloblastic anemia, signs of dorsal column dysfunction, and an elevated methylmalonic acid level.