Megaloblastic Anaemia

Content

·        
Megaloblastic
anemia

·        
Etiology
of megaloblastic anemia

·        
Epidemiology of megaloblastic anemia

·        
Pathogenesis
of megaloblastic anemia

Objectives

At the
end of the PDF Notes, the students will be able to

•       Define  megaloblastic anemia

•       Discuss  the etiology of megaloblastic anemia

•       Describe  the epidemiology of megaloblastic anemia

•       Explain the pathogenesis of
megaloblastic anemia

Megaloblastic Anaemia

•       It is caused by impaired DNA synthesis and others by folate and
vitamin B12 deficiency

•       Abnormality in the haematopoietic precursors in the bone marrow –
maturation of the nucleus is delayed relative to that of the cytoplasm.

•       Formation of morphologically abnormal nucleated
red cell precursor called megaloblast in the bone marrow

•       Anaemia described is hyperchromic macrocytic

Etiological Classification of 

Megaloblastic Anaemia

 I.   VITAMIN B12 DEFICIENCY

A. Inadequate dietary intake e.g. strict
vegetarians, breast-fed infants.

B. Malabsorption

1. Gastric causes: pernicious anaemia,
gastrectomy, congenital lack of intrinsic factor.

2. Intestinal causes: tropical sprue, ileal
resection, Crohn’s disease, intestinal blind loop syndrome, fish-tapeworm
infestation.

II. FOLATE DEFICIENCY

A.      Inadequate dietary intake e.g. in
alcoholics, teenagers, infants, old age, poverty.

B. Malabsorption e.g. in tropical sprue, coeliac disease, partial gastrectomy,
jejunal resection, Crohn’s disease.

C. Excess demand

•       1. Physiological: pregnancy, lactation, infancy.

•       2. Pathological: malignancy, increased haematopoiesis, chronic
exfoliative skin disorders, tuberculosis, and rheumatoid arthritis.

D. Excess urinary folate loss e.g. in active liver disease, congestive heart failure

Pathophysiology of 

Megaloblastic Anaemia

•       The common feature in megaloblastosis is a defect in DNA synthesis
in rapidly dividing cells.

•        RNA and protein synthesis are
impaired.

•        Unbalanced cell growth and
impaired cell division occur since nuclear maturation is arrested.

•        More mature RBC precursors
are destroyed in the bone marrow prior to entering the blood stream
(intramedullary hemolysis)

Vitamin B12

•       Vitamin B12 or cobalamin is a complex organometallic compound having
a cobalt atom situated within a corrin ring.

•       The liver is the principal storage site
of vitamin B12

•       Major source of loss is via bile and shedding of intestinal
epithelial cells.

•        A major part of the excreted
vitamin B12 is reabsorbed in the ileum by the IF resulting in enterohepatic
circulation 

Sources of Vitamin
B12

–      Micro-organisms (Soil, water animal intestine)

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