Diagnosis

Vitamin B12 deficiency

Etiology

Cause [wis][zif]

1. Decreased intake:

   • Strict vegan diet

   • Poverty and malnutrition

2. Poor absorption:

   • Pernicious anemia: an autoimmune disease where autoantibodies attack intrinsic factor resulting in impaired uptake and resulting in vitamin B12 deficiency

   • Previous surgery: gastric bypass, gastrectomy, ileoectomy, short gut syndrome

   • Inflammation: Celiac disease, Crohn disease (terminal ileitis), gastritis, pancreatitis, intestinal parasites

   • Drugs: estrogen contraceptive pills, anticonvulsants, metformin, proton pump inhibitors, nitrous oxide

3. Increased demand:

   • HIV/AIDS, hemolysis, spherocytosis, thalassemia, sickle-cell disease, leukemia, hypersplenism, malaria ++

Pathophysiology [8ef][zif]

1. Vitamin B12 is a cofactor for enzymes:

   • Source: animal products such as red meat, dairy, and eggs

   • Stored in the liver

   • Involved in the synthesis of DNA, fatty acids, and myelin

2. Intrinsic factor is a glycoprotein that is produced by parietal cells in the stomach and is necessary for the absorption of B12 in the terminal ileum

3. Clinical manifestation of B12 deficiency:

   • Hematologic:

     • Macrocytic anemia --> fatigue and pallor

     • Hemolysis --> jaundice

     • Hypersegmented neutrophils

   • Neurologic symptoms:

     • Myelin damage --> neuropathy, ataxia, dementia

     • Failure during development

     • Headache and neuropsychiatric disturbances

   • GI symptoms: glossitis, diarrhea

Complications [zif]

• Impaired development of CNS

• Infertility

• Heart failure due to anemia

• Pregnancy complications

• Birth defects

• Gastric cancer

• Other autoimmune disease (type 1 diabetes, myasthenia gravis, Hashimoto disease, or rheumatoid arthritis)

Epidemiology

Incidence per 100.000 [wis][mym][8ef]

Prevalence per 100.000 [wis][mym][8ef]

Approach

• Blood test: Complete blood count, MCV, serum B12, folate, MMA and homocysteine levels

• Peripheral smear

• Diagnostic criteria: blood levels of vitamin B12 < 148–185 pmol/L (200 to 250 pg/mL)

• Elevated methylmalonic acid levels may also indicate a deficiency

Treatment

1. Dietary supplementation: meat, fish, eggs, dairy products and specially fortified foods

2. Vitamin B12 1000 mcg intramuscular injection once a week for four weeks [zif]

Differential diagnoses

Alcoholism, Drug side effects, Folic acid deficiency, Hemolytic anemia, HIV, Iron deficiency anemia, Lead toxicity, Leukemia, Multiple sclerosis, Syphilis, Thrombotic thrombocytopenic purpura