Megaloblastic Anaemia Presentation PDF

MEGALOBLAS TIC ANAEMIA PRESENTEDBY DR NWANKWO I. G. DEPARTMENT OF HAEMATOLOGY AND BLOOD TRANSFUSION NAUTH, NNEWI  CONTENT OUTLINE:  Introduction  Epidemiology  Aetiology  Folate metablism  Vitamin B12 metabolism  Pathogenesis of MA  Management  Summary  I...

MEGALOBLAS TIC ANAEMIA PRESENTEDBY DR NWANKWO I. G. DEPARTMENT OF HAEMATOLOGY AND BLOOD TRANSFUSION NAUTH, NNEWI  CONTENT OUTLINE:  Introduction  Epidemiology  Aetiology  Folate metablism  Vitamin B12 metabolism  Pathogenesis of MA  Management  Summary  INTRODUCTION  Megaloblastic Anaemia(s) (MAs): A group of anaemias that results from inhibition of DNA synthesis during haemopoiesis, leading to production of large erythroid precursors and RBCs.  MAs are characterized by distinct morphological & functional abnormalities in the bone marrow [megaloblasts (large erythroid precursors) & giant metamyelocytes]  & peripheral blood- [Macrocytes (large RBCs: MCV > 100fl), MCH, normal MCHC) & hypersegmented neutrophils].  MAs are significant causes of morbidity in many parts of the world especially in resource poor countries.  Generally, their response to treatment is excellent  Megaloblastosis- describes a heterogenous group of disorders that share a common morphological characteristics: Nuclear-cytoplasmic asynchrony  Nuclear maturation lags behind cytoplasmic maturation- an arrest in nuclear maturation.  Most apparent in rapidly dividing cells- GIT epithelial cells, hemopoietic cells  Mature RBC precursors are destroyed in the marrow prior to entering the peripheral circulation- INTRAMEDULLARY HEMOLYSIS  EPIDEMIOLOGY  Frequency is highest in countries where malnutrition is rampant, routine supplementation for pregnant women and elderlies is not available.  About 2-4% of the population worldwide.  Studies on MA in Nigeria and Africa are very limited  International statistics show that folate deficiency and pernicious anaemia usually affects individuals >40yrs and its prevalence increases with older population.  AETIOLOGY  Most common cause are deficiencies of the B group of vitamins (folates and vitamin B12).  Acquired abnormalities of cobalamin and folate transport and utilization  In born errors-Congenital abnormalities of folate and cobalamin transport and metabolism, Lesch-Nyhan syndrome, Hereditory orotic aciduria  Drugs  Infections-direct interference on DNA synthesis  PHYSIOLOGY OF FOLATE  Folic acid (Pteroylglutamic acid / PGA) is present in food, it also synthesized by microorganisms.  Most food PGA is conjugated polyglutamates- green leafy vegs, liver, yeast  Before absorption, it is deconjugated to monoglutmate  Mainly in the proximal jejunum, can be absorbed throughout the small intestine  5 -10mg of folate in the liver, storage is limited and folate deficiency develops about 3-6 months  The daily requirement for adults is about 50-150µg (usually < 0.4mg in adults/ 0.6mg in pregnant women).  CAUSES OF FOLATE DEFICIENCY  Diet--- Poor intake/ prep, alcohol use, malnutrition (elderlies, special diet, institutionalized pxs, poverty)  Malabsorption….. Coeliac disease, alcoholism, Tropical sprue, Gluten-sensitive enteropathy, Crohn disease, Lymphoma or amyloidosis of small bowel, Diabetic enteropathy, Intestinal resections or diversions  Increased demand… Pregnancy, lactation, Cell proliferation, chronic haemolytic state- SCD, HS, HE, hyperalimentation, etc  Drugs-- anticonvulsants e.g phenytoin, phenobarbitone, OCPs, folate inhibitors eg  FUNCTIONS OF FOLATE  Folate coenzymes are required for biological reactions of transferring one carbon units from one compound to another. The most important are 1. Synthesis of pyrimidine nucleotide, thymidilate monophosphate (dTMP) from deoxyuridylate monophosphate (dUMP) in DNA synthesis pathway. 2. Methylation of homocysteine to methionine, a precursor of S- adenosylmethionine (SAM) during the reaction above. SAM is critical for nervous system function  FOLATE METABOLISM  Folate is reduced to N5- methyltetrahydrofolate (N5-MTHF) monoglutamate in the intestinal epithelial cells, which is the primary circulating form of THF in blood  N5-MTHF is demethylated and conjugated by addition of 7 or 8 glutamic acid residues → THF  Catalysed by methionine synthase with Vit B12 as coenzyme  Def of Vit B12 traps folate in methylated form and inhibits formation of other forms of THF (folate trap). The N5-MTHF leaks out of the cells due to non conjugation causing tissue folate depletion.  THF or N5,10-methenylTHF or formylTHF is the essential coenzyme in the conversion of dUMP to dTMP in a reaction catalysed by thymidylate synthase.  dTMP is then phosphorylated to deoxythymidine triphosphate (dTTP) that is required for DNA synthesis  Folate deficiency causes reduced N5,10- MTHF and inability to synthesize dTTP from dUMP. The dUMP is then phosphorylated to form deoxyuidine triphosphate (dUTP).  DNA polymerase can not differentiate dTTP from dUTP, the latter is incorperated into the DNA during DNA synthesis in all folate deficient cells.  Although the DNA proof reading function recognizes the error, the process of repair leads to fragmentation of DNA and apoptosis.  The end result is production of cells with arrested nuclear maturation but normal cytoplasmic development (nucleo- cytoplasmic asynchrony) and megaloblatosis results  Ineffective erythropoiesis and shortened RBC lifespan to 30 – 50% (both intramedullary and extramedullary haemolysis):  Increased haem catabolism and iron turnover.  Anaemia with signs of haemolysis (raised bilirubin & LDH)  The intermediaries requiring folate as cofactor for metabolism such as homocysteine, formiminoglutamic acid (FIGLU) accumulate.  All proliferating cells will exhibit megaloblastosis; hence changes are evident in the bone marrow, the buccal mucosa, tongue, small intestine, cervix, vagina and uterus  VITAMIN B12 METABOLISM  Vitamin B12 (Cobalamin vitamins)  Adenosylcobalamin (AdoCbl)- tissue form  Methylcobalamin (MeCbl)- circulates in plasma  Cyanocobalamin (CnCbl) & Hydroxycobalamin (OHCbl): both are metabolically inactive, can be converted to MeCbl or AdoCbl by tissue enzymes.  Cobalamin consists of a corrin ring with a cobalt atom in its centre, attached to nucleotide portion  PHYSIOLOGY OF VIT B12  Daily requirement- 1-2µg  R-protein, either of salivary or parietal cell origin binds to liberated cobalamin from complex dietary proteins  The liver stores enough vitamin B12 for 3years(2-3mg)  Bile also contains vitamin B12 which is available for reabsorption in the intestine-ENTERO HEPATIC CIRCULATION  Due to this, vitamin B12 deficiency takes years to become manifest even if all dietary intake is stopped  CAUSES OF VITAMIN B12 DEFICIENCY DIETARY DEFICIENCY:  This only occurs in strict vegans  The breastfed offspring of vegan mothers are at risk of developing nutritional vitamin B12 deficiency.  Less strict vegetarians often have slightly low vitamin B12 levels but are not tissue vitamin B12-deficient  Drugs eg purine and pyrimidine analogues, nitrous oxide, phenformin, etc GASTRIC FACTORS  Normal gastric acid and enzyme secretion is required for the release of vitamin B12 from the food.  Hypochlorhydria in elderly patients or following gastric surgery can impair the release of vitamin B12 from food.  Total gastrectomy invariably results in vitamin B12 deficiency within 5 years, PERNICIOUS ANAEMIA  This is an autoimmune disorder in which the gastric mucosa is atrophic with loss of parietal cells causing intrinsic factor deficiency.  In the absence of intrinsic factor less than 1% of dietary vitamin B12 is absorbed.  It is common in individuals with other autoimmune disease (Hashimoto's thyroiditis, Graves' disease, vitiligo, hypoparathyroidism or Addison’s disease) or a family history of these.  SMALL BOWEL FACTORS  One-third of all patients with pancreatic insufficiency fail to transfer dietary vitamin B12 from R protein to intrinsic factor.  motility disorders or hypogammaglobulinaemia-can result in bacterial overgrowth and the resulting competition for free vitamin B12 can result in deficiency.  Inflammatory disease of the terminal ileum, such as Crohn's disease, may impair the interaction of the vitamin B12-intrinsic factor complex with its receptor,cubulin receptor.  Ileal resection.  Infestation by Diphylobotrum latum  FUNCTION OF VIT B12  Vit B12 plays an essential role in- 1. Homocysteine to methionine(meCbl)  Vit B12 is essential for conversion of MTHF to THF which is needed for generating N5,10- MTHF the coenzyme for synthesis of dTMP from dUMP in the DNA synthesis pathway  Vit B12 is essential for keeping the folate in the cells’ cytosol in the conjugated form (cobalamin deficiency→ false increase serum folate and decrease in RBC folate.  GIT epithelial change due to cobalamin def. can lead to malabsorption of folate (both serum & RBC folate will decrease) 2. Conversion of methylmalonyl-CoA to succinyl-CoA (AdoCbl as coenzyme).  The defect in degradation of propionyl CoA to methylmalonyl CoA and then to succinyl coA with accumulation of propionyl CoA.  Propionyl CoA then used as a primer for synthesis of fatty acids with odd numbers of carbons instead of acetyl CoA the normal primer.  Incorporation of these abnormal Fatty acids into neuronal membranes leads to abnormal myelination and disrupts membrane function.  Cobalamin deficiency impacts a network of cytokines and growth factors that can be neurotrophic and others neurotoxic. These factors might play a role in cobalamin related neuropathy PATHOGENESIS OF Megaloblastic Anemia  Folate and cobalamin act synergistically in generating thymidillic acid.  Selective reduction in DNA synthesis; while RNA and protein synthesis proceed fairly normally.  Imbalance in cell growth creates a dichotomy between cytoplasmic and nuclear maturation  With each division during erythropoiesis, this dichotomy widens until the cell either dies or omits terminal division making it to survive as an oversized end stage cell (macrocyte) with a shortened lifespan  Accumulation of dead and dying megaloblasts in the marrow creates a spurious appearance of hyperplasia, but with gradual reduction in number of mature cells released from the marrow; eventually progressing to pancytopenia  CLINICAL FEATURES  Anaemia – develops slowly- weakness, light headedness, palpitations, SOB.  Glossitis, N/V, etc  Jaundice – hemolysis  Lemon yellow skin (combination of severe pallor and light jaundice)  Nail pigmentation and change in hair colour (early graying)  Splenomegaly  Neurological manifestation SUMMARY OF NEUROLOGICAL FINDINGS IN VIT B12 DEFICIENCY  Peripheral nerves- Glove and stocking  paraesthesiae  Spinal cord- Subacute combined degeneration  Posterior columns-diminished vibration and proprioception  Corticospinal tracts-upper motor neuron signs  Cerebrum -Dementia  Optic atrophy  Autonomic neuropathy  LABORATORY FEATURES  FBC- low Hb, raised MCV, normal to low WBC-rarely below 2000, normal to moderate reduction in platelets with high PDW.  PBF- anisopoikilocytosis; oval cells, macro-ovalocytes, in severe cases, red cells may show basophilic stippling and howell-jolly bodies, circulating megaloblasts- nucleated rbcs. Hypersegmented neutrophils  Reticulocyte count- low, may be normal  Serum Vit B12 and folate assay. PERIPHERAL BLOOD SMEAR: HYPERSEGMENTED NEUTROPHILS  MORPHOLOGICAL CHANGES IN BONE MARROW  This ineffective erythropoiesis results in an expanded hypercellular marrow.  The megaloblastic changes are most evident in the early nucleated red cell precursors,  Nuclear changes are seen in the immature granulocyte precursors and a characteristic appearance is that of 'giant' metamyelocytes with a large 'sausage- shaped' nucleus.  The mature neutrophils show hypersegmentation of their nuclei, with cells having six or more nuclear lobes. NUCLEO-CYTOPLASMIC ASYNCHRONY  DIAGNOSTIC WORK UP  The evaluation of suspected folate and B12 def involves two stages:  Establishing vitamin deficiency  determining its cause (e.g. pernicious anaemia, malabsorption, dietary lack)  Low serum folate levels (fasting blood sample)  Red cell folate levels are low (but may be normal if folate deficiency is of very recent onset)  A serum folic acid level less than 2 ng/ml is consistent with folic acid deficiency, as Corroborative findings  Macrocytic dysplastic blood picture  Megaloblastic marrow  measurement of the serum cobalamin concentration  evaluation of specific metabolites (e.g. homocysteine and methyl malonyl coA levels)- diff the two, solitary folate def will show normal MMA level with marked elevation of homocysteine  use of the Schilling test to establish malabsorption of cobalamin  Assay for Intrinsic factor antibodies DIFFERENTIAL DIAGNOSIS  Alcoholism  Liver disease  Hypothyroidism  Aplastic anaemia  Myelodysplasia  Pregnancy  Autoimmune hemolytic anaemia  TREATMENT  Megaloblastic anaemia with established cobalamine def should be given - IM cobalamin 1000µg weekly  OR 3times weekly x 2wks + once weekly for 6weeks/ until Hb returns to normal.  OR orally at 1000-2000µg daily  In pernicious anaemia, partial or total gastrectomy- cobalamin is given monthly for life.  Patients with neurological and mental impairment from Vit B12 def require aggressive approach-parenteral  There is a need to apply multidisciplinary approach to management of megaloblastic anaemia- Haematologist, neurologist, gastroenterologist, and paediatricians.  In folate def, folic acid at doses 1-5mg daily is given x 3mths  Must rule out cobalamine deficiency before commencement of folic acid.  Response is monitored with FBC, LDH/UB(drops), retic count(rises by 3- 5days), Hb should rise by 1g/dl weekly and within normal value by 2mths.  Potassium should be closely monitored as it falls with treatment.  SUMMARY  MAs are heterogeneous group of disorders that share common morphologic characteristics. The morphological hallmark of megaloblastic anaemias is megaloblastic erythropoiesis.  The cellular enlargement is due to impaired DNA synthesis which causes lagged nuclear maturation and cell division → nuclear / cytoplasmic asynchrony  Precursors of other cell lines in the BM are also affected if def. is severe, the BM output for other cells (granulocytes and platelets) also diminish and patient may present with pancytopenia.