Megaloblastic anemias

Megaloblastic anemia

Megaloblastic anemias constitute a diverse group of entities with-

1. Impaired DNA synthesis

2. Megaloblastic changes in blood & BM due to nuclear : cytoplasmic asynchrony

Etiologies : Vit B12 def. including Pernicious anemia, Folate def.

PATHOGENETIC CLASSIFICATION OF NON MEGALOBLASTIC MACROCYTIC ANEMIA

Associated with accelerated erythropoiesis Hemolytic anemia

Post haemorrhagic anemia

Alcoholism

Liver disease

MDS

Myelophthistic anemia

Acquired sideroblastic anemia

Hypothyroidism

CDA(TYPES I &III)

DIAMOND BLACKFAN SYNDROME

Intracellular substances: Folate and Cobalamin

Folate Pteridine ring, glutamate side chain Enzymatically active form is tetra-hydrofolate (THF) Intermediate in transfer of one carbon units Involved in purine, pyrimidine metabolism, and s-

adenosyl methione (S-Adomet) generation

Cobalamin Cobalt-tetrapyrrole ring Cobalamin forms

Methylcobalamin Adenosylcobalamin Cyanocobalamin

Cobalamin deficiency traps folate

Folic acid THF

Methyl-THF

Homocystiene Methionine

M

Methyl-cobalamin

Methylene-THF

Serine

Glycine

P Pyridoxal-5-phosphate

Cobalamin deficiency Inhibits Methionine synthesis It also traps Methyl-THF, and activates more methylene THF to be converted to Meth-THF Internal THF deficiency ensues,yield of less polyglutamated forms. Excess homocysteine is converted to Cysteine, which is toxic to cells

Cystiene

DHF

dUMP dTMP

mthfr

Folate and cobalamin help amino-acid synthesis

THF Methyl-THF

Homocystiene Methionine

M

M Methyl-cobalamin

S-AdoMet S-Ado- homocyctiene

Methyl-acceptor Methylated product

Folic acid

S-Ado-Meth is regulator of folate metabolism,inhibits mthfr

S-Ado-met is also a methyl donor and hence has a role in amino-acid synthesis

Folate and Cobalamin deficiency inhibit amino-acid synthesis

Metabolic effects of B12 & folic acid

Methyl malonyl CoA Succinyl malonyl CoA

accumulates

Abnormal fatty acids myelin breakdown & neurologic complications

Histidine FIGLU glutamate + formimino FH4

B12 MMCoA mutase

FH4

Folate absorption Dietary sources - Food folate - Folic acid

Intestinal transporter

Folic acid THF

Meth-THF

Meth-THF

Mu

cosal cell

Blo

od

vessel

Proximal jejunum Saturable absorption

Terminal ileum Non-saturable absorption

Tissues

Folate receptor

Rapid absorption

Intestinal transporter

Folic acid THF

Meth-THF

Meth-THF

Folate stores

In liver and red cells

Polyglutamate form

Total content:5-20 mg,exhausted in 4 mths

Normal loss through sweat,saliva.urine.faecus

Cobalamin absorption Dietary sources - Animal produce

Meth-THF

Blo

od

vessel

Gastric mucosa

Cubulin receptor

TC-II

Proteases

IF

Ileal mucosa

TC-II-R Tissu

e

R-B12 complex

Duodenum

Pancreas

Cobalamin stores

Liver is the principle site

Also present in kidney,heart and brain

Storage form is adenosyl-cobalamin

Major routes of loss through biliary excretion and desquamation of intestinal epithelial cells

Folate vs Cobalamin

Folate

RDA 400ug adults; 600ug pregnant women

Fresh vegetables, fruits, dairy, meats.

Absorption in proximal and distal small intestine

Does not involve specific binding proteins for absorption and transport

Storage form is limited, RDA essential. Development of deficiency rapid.

Cobalamin

RDA 2.5ug in adults

Present in animal sources Milk cheese eggs

Absorption in distal small intestine

Requires specific binding proteins (IF, TC-II)

Stored in body, excretion is limited. Development of deficiency is slow.

Folate vs Cobalamin

Folate

Deficiency due to Poor dietary intake

Increased requirement

Alcoholism

Anti-folate drugs

Extensive intestinal resection

Cobalamin

Deficiency due to Poor intake (vegans)

IF deficiency (pernicious anemia)

Inflammatory bowel disease

Ileum resection

Gastrectomy

Fish tapeworm

Combined deficiency Tropical sprue Gluten sensitive enteropathy

Pernicious anemia

Autoimmune des. of gastric mucosa leading to chronic atrophic gastritis parietal cell loss decreased IF release B12 def

I Ab blocks binding of B12 to IF

II Ab blocks binding of IF-B12 to ileal R

III Ab not specific

Auto-reactive T cell mediated injury

Pernicious anemia

Similar blood and bone-marrow findings

Atrophy of fundic glands

Intestinal metaplasia

Atrophic glossitis

CNS lesions (SACD of dorso-lateral tracts)

Consequences of folate and cobalamin deficiency

Manifest deficiency Megaloblastic anemia

Altered DNA synthesis

Nuclear cytoplasmic asynchrony

Neurological dysfunction Altered myelin synthesis

Subacute combined degeneration

Mucosal abnormalities (Glossitis)

Subclinical deficiency Hyper-homocystienemia

Atherosclerosis

Hematological findings

Affects all three series of cells

Anemia, Dyserythropoiesis

Leukopenia

Thrombocytopenia

Affects cellular maturation

Megaloblasts in marrow

Macrocytes in peripheral smear

Hypersegmented neutrophils

Peripheral smear

Hypersegmented neutrophils

Macrocytes

Vit B12 def.

S.Vit B12 (N 160-900ng/l)

Homocysteine,S. methyl malonic acid

IF antibodies

Folic acid def

S. folic acid

FIGLU in urine (intermediate product in conversion of histidine to glutamate)

Biochemical findings

Tests for diagnosis

Test Cobalamin def Folate def Discriminating capacity

S.cobalamin N or Fair to good

S.folate N or

Very good

Red cell folate or n

poor

S.Methylmalonyl acid

N Very good

De-oxyuridine suppression test

abnormal abnormal Very good

Schillings test

Stage I Oral dose radiolabelled, 1ug Parenteral dose 1000 microg 24 hr urine N >10%, PA

Stage II : repeat with IF supplements

Schillings test : radioactive B12 is used to assess status of IF and VitB12 ; to distinguish PA from other causes of B12 def.

Megaloblastic anemia: Bone Marrow

BM : hypercellular, may completely replace the fatty marrow

M:E is reversed Megaloblasts larger in

size, open seive-like chromatin and well hemoglobinized cytoplasm

Giant metamyelocytes and band forms

Megakaryocytes large and bizarre multilobate nuclei

Reversal of symptoms

New reticulocytes: 2-3 days

LDH and s.bilirubin decline

Neutrophil hypersegmentation persists for 2 wks or more

WBC and platelets: 1 wk

Peak retic:10 days (hb increases)

Fully normal:8 weeks,neurological manifestations first few wks