MEGALOBLASTIC ANEMIA – Types, Etiology, Clinical Manifestation, Diagnostic Evaluation and Management
Megaloblastic anemia are a group of disorders caused by impaired DNA synthesis and characterized by the presence of large RBC’s. When DNA synthesis is impaired, defective RBC maturation result. The RBC’s are large (macrocytic) and abnormal and are referred to as megaloblasts.
It is caused by deficiency of vitamin B12 or folic acid, this type of RBC deformity can also occur from suppression of DNA synthesis by drugs.
- Cobalamin (vitamin B12) deficiency
- Folic acid deficiency
Cobalamine (Vitamin B12) deficiency
It is also known as pernicious anemia. It is caused by decreased absorption of vitamin B12. Normally a protein termed intrinsic factor is secreted by the parital cells of the gastric mucosa. Intrinsic factor is required for cobalamin absorption. Therefore intrinsic factor is not secreted cobalamin will not be absorbed (cobalamin is normally absorbed in the distal ileum).
Folic acid Deficiency
- People who rarely eat uncooked vegetables.
- Alcohol increases folic acid requirements and have diet deficient in vitamin.
- Patients with chronic hemolytic anemias and women who are pregnant.
- Patients with malabsorptive diseases of the small bowel, such as sprue, may not absorb folic acid normally.
Vitamin B12 Deficiency
- Inadequate dietary intake; who consume no meat or dairy products.
- Faulty absorption from gastrointestinal tract such as Crohn’s disease, or after ileal resection or gastrectomy.
- Absence of intrinsic factor, as in pernicious anemia. Without intrinsic factor, orally consumed vitamin B12 cannot be absorbed, and RBC production is eventually diminshed.
Signs and symtoms of vitamin deficiency anemia include:
- Shortness of breath
- Pale or yellowish skin
- Irregular heartbeats
- Numbness or tingling in your hands and feet
- Muscle weakness
- Personality changes
- Unsteady movements
- Mental confusion or forgetfulness.
Vitamin deficiencies usually develop slowly over several months to years. Vitamin deficiency symptoms maybe subtle at first, but hey increase as the deficiency worsens.
- The number and appearance of red blood cells: people with anemia have fewer red blood cells than normal. In vitamin deficiency anemia related to a lack of vitmin B12 and folate, the red blood cells appear large and under developed. In advanced deficiencies, the numbers of white blood cells and platelets also might be decreased and look abnormal under a microscope.
- The amount of folate, vitamin B2 and vitamin C in blood: Folate and vitamin B12 levels are measured at the same time because these deficiences can cause cause similar signs ans symptoms.
- Antibodies test: A sample of blood to check for antibodies to intrinsic factor. There presence indicates pernicious anemia.
- Methylmalonic acid test: To measure the presence of a substance called methylmalonic acid. The level of this substance is higher in people with vitamin B12 deficiency.
- Schilling test: In this test, first ingest a tiny amount of radioactive vitamin B12. Then blood is checked, if body absorbed the vitamin B12 or not. After that, ingest a combination of radioactive vitamin B12 and intrinsic factor. If the radioactive B12 is absorbed only when taken with intrinsic factor, it confirms that lack of intrinsic factor.
- Increasing amount of folic acid in diet and administering 1 mg of folic acid daily.
- Folic acid administered intramuscularly only for people with malabsorption problems.
- After hemoglobin level returns to normal, folic acid replacement can be stopped.
- Vitamin B12 deficiency treated by vitamin B12 replacement.
- Vegetarian supplements through vitamins or fortified soy milk.
- If deficiency due to defective absorption or absence of intrinsic factor, replacement is by monthly intramuscular injections of vitamin B12, usually at a dose of 1000 µg. to prevent recurrence, vitamin B12 therapy must be continued for life.