​Symptoms and Signs – Differential Diagnosis of Cobalamin Deficiency

​Symptoms and Signs – Differential Diagnosis of Cobalamin Deficiency
NUTRITIONAL COBALAMIN DEFICIENCY (I.E., INSUFFICIENT COBALAMIN INTAKE)
• Vegetarians, poverty-imposed near-vegetarians, breast-fed infants of mothers with pernicious anemia

ABNORMAL INTRAGASTRIC EVENTS (I.E., INADEQUATE
PROTEOLYSIS OF FOOD COBALAMIN)
• Atrophic gastritis, partial gastrectomy with hypochlorhydria, proton pump inhibitors, H2 blockers

LOSS OR ATROPHY OF GASTRIC OXYNTIC MUCOSA (I.E., DEFICIENT INTRINSIC FACTOR [IF] MOLECULES)
• Total or partial gastrectomy, pernicious anemia, caustic
destruction (lye)

ABNORMAL EVENTS IN SMALL BOWEL LUMEN
• Inadequate pancreatic protease (e.g., R-cobalamin not degraded, cobalamin not transferred to IF)
• Insufficient pancreatic protease (i.e., pancreatic insufficiency)
• Inactivation of pancreatic protease (i.e., Zollinger-Ellison syndrome)
• Usurping of luminal cobalamin (i.e., inadequate cobalamin binding to IF)
• By bacteria; during stasis syndromes (e.g., blind loops, pouches of diverticulosis, strictures, fistulas, anastomosis); impaired bowel motility (e.g., scleroderma); hypogammaglobulinemia
• By Diphyllobothrium latum (fish tapeworm)

DISORDERS OF ILEAL MUCOSA/IF-COBALAMIN RECEPTORS (I.E., IF-COBALAMIN NOT BOUND TO IFCOBALAMIN RECEPTORS)
• Diminished or absent IF-cobalamin receptors (e.g., ileal bypass, resection, fistula)
• Abnormal mucosal architecture/function (e.g., tropical or nontropical sprue, Crohn’s disease, tuberculous ileitis, infiltration by lymphomas, amyloidosis)
• IF/post IF–cobalamin receptor defects (e.g., Imerslund-Graesbeck syndrome, transcobalamin II [TC II] deficiency)
• Drug effects (e.g., Slow-K, metformin, cholestyramine, colchicine, neomycin)

DISORDERS OF PLASMA COBALAMIN TRANSPORT (I.E., TC II–COBALAMIN NOT DELIVERED TO TC II RECEPTORS)
• Congenital TC II deficiency, defective binding of TC II–cobalamin to TC II receptors (rare)

METABOLIC DISORDERS (I.E., COBALAMIN NOT USED BY CELLS)
• Inborn enzyme errors (rare)
• Acquired disorders (e.g., cobalamin functionally inactivated by irreversible oxidation, N2O inhalation)