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Vitamin B12 deficiency
From WikEM
(Redirected from Pernicious anemia)
Contents
Background
- Vitamin B12, also known as cobalamin, cyanocobalamin
- Ingested in dietary form
- Binds to intrinsic factor, a protein secreted by gastric parietal cells
- B12-intrinsic factor complex then absorbed in the terminal ileum
- Stored in liver, takes up to 3 years to deplete hepatic stores after ceasing intake
- Causes of deficiency:
- Decreased intake (e.g. strict vegan diet)
- Competition in gut (e.g. blind loop syndrome, fish tapeworm)
- Intrinsic factor deficiency
- Pernicious anemia (associated with atrophic gastritis, IgA deficiency, polyglandular endocrine failure)
- Post-gastrectomy
- Decreased ileal absorption (e.g. post ileectomy, Crohn's disease
- Pancreatic insufficiency
- H. pylori infection
Clinical Features
- Hematologic
- Signs/symptoms of anemia
- May be relatively asymptomatic due to slow onset
- Signs/symptoms of pancytopenia
- Signs/symptoms of anemia
- Neurologic
- Paresthesias
- Peripheral neuropathy
- Dorsal column demyelination (proprioception, vibration sensation abnormalities)
- Psychiatric
Differential Diagnosis
Anemia
RBC Loss
- Hemorrhage
RBC consumption (Destruction/hemolytic)
- Hereditary
- Acquired
- Microangiopathic Hemolytic Anemia (MAHA)
- Autoimmune hemolytic anemia
Impaired Production (Hypochromic/microcytic)
- Iron deficiency
- Anemia of chronic disease
- Thalassemia
- Sideroblastic anemia
Aplastic/myelodysplastic (normocytic)
Megaloblastic (macrocytic)
- Vitamin B12/folate deficiency
- Drugs (chemo)
- HIV
Altered mental status
Diffuse brain dysfunction
- Hypoxic encephalopathy
- Acute toxic-metabolic encephalopathy (Delirium)
- Hypoglycemia
- Hyperosmolar state (e.g., hyperglycemia)
- Electrolyte Abnormalities (hypernatremia or hyponatremia, hypercalcemia)
- Organ system failure
- Hepatic Encephalopathy
- Uremia/Renal Failure
- Endocrine (Addison's disease, Cushing syndrome, hypothyroidism, myxedema coma, thyroid storm)
- Hypoxia
- CO2 narcosis
- Hypertensive Encephalopathy
- Toxins
- Drug reactions (NMS, Serotonin Syndrome)
- Environmental causes
- Deficiency state
- Wernicke encephalopathy
- Subacture Combined Degeneragion (B12 deficiency)
- Vitamin D Deficiency
- Zinc Deficiency
- Sepsis
Primary CNS disease or trauma
- Direct CNS trauma
- Diffuse axonal injury
- Subdural/epidural hematoma
- Vascular disease
- Intraparenchymal hemorrhage
- SAH
- Stroke
- Hemispheric, brainstem
- CNS infections
- Neoplasms
- Paraneoplastic Limbic Encephalitis]
- Malignant Meningitis
- Pancreatic Insulinoma
- Seizures
- Nonconvulsive status epilepticus
- Postictal state
- Dementia
Psychiatric
- Acute psychosis
- Excited delirium
- Malingering
General Psychiatric
- Organic causes
- Psychiatric causes
- Guillain-Barre syndrome
- Toxins (Ciguatera)
- Tick paralysis
- Diabetic neuropathy
Evaluation
- CBC, peripheral smear, reticulocyte count
- Macrocytic anemia (MCV>100 fL), usually moderate to severe
- High RDW
- Low reticulocyte count
- Hypersegmented neutrophils
- If severe, low WBC and low platelets
- Serum B12
- Normal: > 210 pg/mL
- Deficiency: <170 pg/mL
- Symptomatic patients usually have levels <100 pg/mL
- LDH, bilirubin may be elevated
- Evaluate for underlying causes and complications
Management
- Vitamin B12
- Normal absorption: 1000 mcg/day PO
- Malabsorption: 100-1000 mcg IV/IM or deep SC injection daily for 6 or 7 days
- Nasal spray: 500 mcg intranasally in one nostril weekly
- Folic acid: 1mg daily
- Transfusion rarely needed
