This patient presents with paresthesias, ataxia, abdominal pain, jaundice, weight loss, and macrocytic anemia (increased mean corpuscular volume). There are many causes of paresthesias but most do not apply in this case. The patient’s ataxia and anemia narrow the focus greatly. His symptoms of shortness of breath and fatigue may be explained by the severe anemia.
On examination, he shows decreased sensation, normal strength, and a positive Romberg test: when he closes his eyes, the positional input from his lower extremities and spinal cord posterior columns is inadequate to maintain balance. Because he does not have signs of hereditary ataxia, infection (tabes dorsalis, leprosy, HIV), diabetes, alcoholism, multiple sclerosis, or multisystem atrophy, nutritional deficiencies are most likely. Inadequate levels of vitamin B12, folate, and vitamin E can cause sensory ataxia. Although other tests can be done to exclude HIV or syphilis, the presence of paresthesias and macrocytic anemia makes vitamin B12 or folate deficiency the most likely cause. Severe vitamin B12 or folate deficiency causes subacute degeneration of the dorsal columns of the spinal cord and hemolysis, with increased lactate dehydrogenase and total and unconjugated bilirubin levels, as well as nonspecific abdominal pain and weight loss. Hemolysis occurs because of ineffective erythropoiesis, with hemolysis of abnormal megaloblastic erythroid precursors.
Examination of the red cell smear will show hypersegmented neutrophils (>5 lobes), oval macrocytes, and anisocytosis. The patient should have vitamin B12 and RBC folate levels checked. However, methylmalonic acid and homocysteine levels can differentiate between vitamin B12 and folate deficiency, because methylmalonic acid is increased in both conditions and homocysteine is increased only in folate deficiency.
Causes of vitamin B12 deficiency include inadequate diet, pernicious anemia (inadequate intrinsic factor), and infections such as Helicobacter pylori and fish tapeworm. Severe deficiency is treated initially with intramuscular vitamin B12.
Abdominal conditions, spinal cord problems, and thyroid disease would not cause the symptoms and signs in this case, and thus assessment for these would not be the best next step. Bone marrow aspirate and biopsy would be abnormal and show signs of megaloblastic anemia; however, it is not necessary to establish the diagnosis.
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