Chukwuemeka.W. Israel 1403 MEGALOBLASTIC ANAEMIA

Introduction Characterized by inhibition of DNA synthesis during red blood cell production. When DNA synthesis is impaired, the cell cycle cannot progress from the G2 growth stage to the mitosis (M) stage. This leads to continuing cell growth without division, which presents as macrocytosis. Most commonly result from lack of folic acid or vitamin B 12

MEGALOBLASTIC ANAEMIA [ VITAMIN B 12 DEFICIENCY ]

Sources The best sources of Vitamin B12 include: eggs, milk, cheese, milk products, meat, fish, shellfish and poultry. Some soy and rice beverages as well as soy based meat substitutes are fortified with vitamin B12. Although bacteria in the large intestine synthesize vitamin B 12 it cannot be absorbed from this site

Absorption of Vitamin B 12  2 mechanism Active (75%) – requires the presence of intrinsic factor ( a glycoprotein produced by gastric mucosa) Passive – absorption occurs by diffusion and works when pharmacological doses of vitamin B 12 are ingested  Minimum amount required for an adult is 1 to 4 µg per day

Vitamin B12 in food R-Binder B12-R-Binder complex IF-B12 complex + Freed R-Binder Intrinsic Factor (IF) Receptor-IF-B12 B12-TCII Circulation Receptor TCII IF Degradation Epithelial cell of terminal iIeum Stomach Duodenum

Functions of Vitamin B 12 Plays a key role in the normal functioning of the brain and nervous system Erythropoesis Synthesis of methionine from homocysteine Conversion of methyl malonyl CoA to succinyl CoA

FH4 FH2 Methylene FH4 Methyl FH4 Intestinal cell Dietary folates Dihidrofolate Redutase Methionine Homocysteine Thymidylate Synthase DNA Synthesis dTMPdUMP Role of Vitamin B12 and Folate in DNA synthesis VitB12 (Methylcobalamin)

General Morphological Features Of Megaloblastic Anemia

PERIPHERAL BLOOD FINDINGS 1. Hemoglobin – decreased 2. Hematocrit – decreased 3. RBC & Platelet count – decreased/normal 4. MCV - >100fl (normal 82-98fl) 5. MCH –increased 6. MCHC – Normal (32–36 g/dL) 7. Reticulocytopenia- due to destruction of fragile and abnormal megaloblastic erythroid precursor. 8. Howell-Jolly bodies (chromosomal remnant) also present. 9. Hypersegmented Neutrophils 10. Poikilocytosis (abnormally shaped RBCs).

PERIPHERAL SMEAR  RBC: - Macro-ovalocytosis [ macrocytosis is the earliest sign in Vit B 12 deficiency and can be detected even before the onset of anaemia ] - In severe anaemia in addition to macrocytosis, marked anisopoikilocytosis, basophilic stippling, howell jolly bodies may be found

Marked macro-ovalocytosis (MCV 134 fl) in the peripheral blood smear of a patient with vitamin B12 deficiency.

PERIPHERAL SMEAR  WBC Normal count or reduced count Hypersegmented neutrophils is one of the earliest sign of megaloblastic haematopoiesis and can be detected even in the absence of anaemia (when more than 5% of neutrophils show ≥ 5 lobes; 1% neutrophils with ≥ 6 lobes)  PLATELETS: Normal or decreased (severe anaemia) Giant platelet can occur

MEGALOBLAST 1. Cell and nuclear size and amount of cytoplasm (deeply basophilic royal blue) are increased 2. Nuclear chromatin is sieve like or stippled (open) 3. Nuclear cytoplasmic asynchrony/dissociation 4. Abnormally large precursor (promegaloblast and early megaloblast) are increased in BM – Maturation arrest 5. Abnormal mitoses (increased)

Causes of Vit B 12 deficiency Insufficient dietary intake (very rare) Strict vegetarians Deficient absorption Pernicious anaemia Total or partial gastrectomy Prolonged use of PPI or H 2 blockers Diseases of small intestine(crohns disease,intestinal cancer,celiac disease) Fish tapeworm infestation

FOLIC ACID DEFICIENCY

Causes Poor folate diet -Alcoholism -Severe poverty Increased folate requirement -Prgnancy -Hemolytic anemia Drug therapy Malabsorption

Manifestations Megaloblastic Anemia A lack of energy Sore and red tongue Muscle weakness Depression Problems with memory, understanding and judgement

PERNICIOUS ANEMIA CHRONIC ATROPHIC GASTRITIS -autoimmune destruction of gastric mucosa marked loss of parietal cells which are responsible, in part, for the secretion of intrinsic factor, a protein essential for subsequent absorption of vitamin B12 in the ileum. Pathological changes are infiltration by mononuclear cells in submucosa and lamina propria of fundus and body of the stomach, progressive loss of parietal and chief cells, and their replacement by intestinal type mucous cells

H. pylori and Zollinger-Ellison syndrome may also cause a form of nonautoimmune gastritis that can lead to pernicious anemia Patients with pernicious anaemia have increase risk of gastric cancer

DIAGNOSTIC FEATURES 1. Moderate to severe megaloblastic anemia 2. Leucopenia with hypersegmented neutrophils 3. Mild to moderate thrombocytopenia 4. Mild jaundice due to ineffective erythropoiesis and peripheral hemolysis 5. Neurologic changes 6. Low levels of serum B 12

7. Elevated levels of homocysteine 8. Striking reticulocytosis after parenteral administration of vitamin B Serum antibodies to intrinsic factor (specific) and anti parietal cell antibodies in serum 10. Abnormal Schilling test

GASTRECTOMY Total gastrectomy : Secondary to Vit B 12 deficiency as it removes the site of synthesis of intrinsic factor Prophylactic vitamin B 12 after surgery Partial gastrectomy Regular follow up after surgery for early detection of deficiency

INFESTATION BY FISH TAPEWORM Diphyllobothrium latum (inadequately cooked fish) Vitamin deficiency by competing with the host for vitamin in food Diagnosis made by demonstration of ova in stool

CLINICAL FEATURES Anaemia, mild jaundice and sometimes neurological involvement Neurological involvement in the form of Peripheral neuropathy Subacute combined degeneration of spinal cord Cerebral changes (personality changes, dementia & psychosis) Patients can present with only neurological abnormalities without megaloblastic anaemia

LABORATORY FEATURES 1. Morpholgical changes of megaloblastic anaemia in PS and BM 2. Serum vitamin B 12 assays 3. Methylmalonic acid (MMA) and homocysteine in serum 4. Abnormal Schilling test 5. Intrinsic factor antibodies in serum

MANAGEMENT OF B 12 DEFICIENCY When B 12 deficiency is suspected a trial of B 12 is essential. Failure of response can only be determined after careful follow-up over a period of several months, particularly if the patient is non-anaemic. Standard therapy for all cases of B 12 deficiency is by regular intramuscular injections of B 12, usually in the form of hydroxycobalamin. In patients with inadequate dietary intake supplements may be given by mouth. Underlying conditions should be managed separately.

After initiation of therapy, reticulocyte count begins to increase around 3 rd day – peak by 6 th or 7 th day – gradually returns to normal by end of 3 rd week Hematocrit steadily rises and normalises in about 1-2 months Blood transfusion is indicated in severely anaemic symptomatic patients or in patients with CCF

NOTE: Both B 12 and folate are given to patients if B 12 deficiency has not been excluded. This is to prevent neurological damage, e.g. subacute combined degeneration of the spinal cord.