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| {{Vitamin B12 deficiency}}
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| == Common Causes ==
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| === Decrease intake ===
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| * Strict vegan diet more than 3 years .
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| * Breast fed infants of pure vegan may also develop deficiency .
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| * Malnutrition most likely happen in elderly patients.
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| === Malabsorption ===
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| * Decrease intrinsic factor due autoimmune destruction of parietal cell.
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| * Decrease Gastric acid production due to proton pump inhibitor and histamine 2 receptor antagonists
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| * Gastric by pass surgery because intrinsic factor is produce by parietal cell of stomach
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| * Tapeworm (Diphyllobothrium latum ) ingested from contaminated fish , tapeworm saps nutrients
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| * Crohn's disease
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| === Increased requirement ===
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| * pregnancy
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| == Pathophysiology ==
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| * Dietary Vitamin B12 binds to salivary R factor then the complex arrives at small intestine
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| * In duodenum Vitamin B12 is detach from R- factor by pancreatic proteases
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| * Now free B12 binds to intrinsic factor which is secreted by gastric parietal cell
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| * The intrinsic factor - B12 complex is absorbed in the ileum
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| * Absorbed vitamin B12 is use in metabolic pathways which is important for neurologic and hematologic function if vitamin B12 is deficit regardless of the cause many impairments may occur
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| * Vitamin B12 is a cofactor for the enzyme methionine synthase which convert homocysteine to methionine as a result methyl- THF is converted to THF which is use in synthesis of pyrimidine base of DNA.
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| * In B 12 deficiency homocystein accumulate which cause megaloblastic anemia and hypersegmented neutrophils.
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| *Vitamin B 12 is a cofactor for enzyme methylmalonyl-COA mutase , which converts methylmalonic-COA to succinyl-COA. In B 12 deficiency methylmalonic acid (MMA ) will accumulate. MMA and elevated level of homocysteine cause damage of myelin as a result subacute combined degeneration of spinal cord ( SCDSC ) occur . This affects dorsal columns, lateral corticospinal tracts and spinocerebellar tract as result loss of proprioception , ataxia , peripheral neuropathy and dementia.
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| == Laboratory Finding ==
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| * Initial lab tests is a complete blood count (CBC) with a peripheral smear and serum B12 and folate levels.
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| * In some cases needed to check methylmalonic acid (MMA ) and serum homocysteine levels.
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| * With above elevated finding macrocytic anemia and peripheral blood smear show hypersegmented neutrophils .
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| ==References== | | ==References== |
| {{Reflist|2}} | | {{Reflist|2}} |