Megaloblastic anaemia (class lecture for v year mbbs)

1. Megaloblastic anaemia
Prof Mona Aziz Gilani
FCPS(haematology)
Shaikh Zayed PGMI and
Shaikh Khalifa bin Zayed
Medical College,
Lahore
Pakistan

2. Megaloblastic anaemia
This results from a
• Deficiency of vitamin B12
• Or/and
• Folic acid
• or
• from disturbances in folic acid metabolism.

3. Pathogenesis
• Folate is an important substrate of, and vitamin B12 a co-factor for,
the generation of the essential amino acid methionine from
homocysteine.
• This reaction produces tetrahydrofolate, which converts uracil MP to
thymidine monophosphate for incorporation into DNA.

4. Pathogenesis …
• Deficiency of either vitamin B12 or folate will therefore produce high
plasma levels of homocysteine and impaired DNA synthesis
• The end result is cells with arrested nuclear maturation but normal
cytoplasmic development: so-called nucleocytoplasmic asynchrony.

6. Is DNA production of every cell in body
impaired ?
• All proliferating cells will exhibit megaloblastosis
• Changes are evident in the buccal mucosa, tongue, small intestine,
cervix, vagina and uterus.
• The high proliferation rate of bone marrow results in striking changes
in it .
• Cells become arrested in development and die within the marrow
• this ineffective erythropoiesis results in an expanded hypercellular
marrow

7. Changes in BM
• The megaloblastic changes are most evident in the early nucleated
RBC precursors, and
• haemolysis within the marrow results in a raised bilirubin and lactate
dehydrogenase (LDH), but without the reticulocytosis characteristic of
other forms of haemolysis
• Iron stores are usually raised.
• Nuclear changes are also seen in the WBC precursors and a
characteristic appearance is that of ‘giant’ metamyelocytes with a
large ‘sausage-shaped’ nucleus.

8. Changes in blood
• The mature red cells are large and oval, and sometimes contain
nuclear remnants.
• The mature neutrophils show hyper-segmentation of their nuclei,
with cells having six or more nuclear lobes.
• If severe, a pancytopenia may be present in the peripheral blood.

9. Why neurological changes ?
• Vitamin B12 deficiency, but not folate deficiency, is associated with
neurological disease in 40%
• advanced neurological disease due to B12 deficiency is now
uncommon in the developed world.
• Cause …The main pathological finding is focal demyelination affecting
the spinal cord, peripheral nerves, optic nerves and cerebrum.
• The most common manifestations are sensory

11. Vitamin B12
• Daily requirement ….. 1.8-2.8 μg
• The average daily diet contains 5–30 μg of vitamin B12
• Sources are meat, fish, eggs and milk

12. Plants are not sources of Vit.B12

13. Vitamin B12 absorption
• In the stomach, gastric enzymes release vitamin B12 from food
• At gastric pH it binds to a carrier protein termed R protein.
• The gastric parietal cells produce intrinsic factor, a protein that
optimally binds vitamin B12 at pH 8.
• As gastric emptying occurs, pancreatic secretion raises the pH and
vitamin B12 released from the diet switches from the R protein to
intrinsic factor.
• Bile also contains vitamin B12 that is available for reabsorption in the
intestine.

14. • B12–IF complex binds to specific receptors in the terminal ileum
• vitamin B12 is actively transported by the enterocytes to plasma
• in plasma it binds to transcobalamin II (a transport protein produced
by the liver)
• which carries it to the tissues for utilisation.

15. • .
• Vitamin B12 absorption
depends on various factors :
R-factor,
Intrinsic factor &
Transcobalamin 2.

16. Vitamin B -12 storage
• The liver stores enough vitamin B12 for 3 years
• There is also an enterohepatic circulation
• Vitamin B12 deficiency takes 2-3 years to become manifest, even if
all dietary intake is stopped or severe B12 malabsorption supervenes
• Blood levels of vitamin B12 are indicator of tissue stores
• Normal level …200-900 pg/ml

17. Normal variations in B12
• in normal pregnancy
• Levels of cobalamins fall
• Levels below 150 pg/ml are common
• in the last trimester, 5–10% of women have levels below 100 pg/ml
• Spuriously low B12 values
• women using the oral contraceptive pill
• in patients with myeloma (paraproteins can interfere with vitamin
B12 assays).

18. Causes of vitamin B12 deficiency
1. Dietary deficiency
• Only in strict vegans
• Vegetarians often have slightly low vitamin B12 levels but are not
tissue vitamin B12-deficient.

19. 2. Gastric pathology
• Hypochlorhydria in elderly patients or following gastric surgery.
• Total gastrectomy
• In 100% ,develops within 5 years, often combined with iron
deficiency; need life-long 3-monthly vitamin B12 injections.
• After partial gastrectomy,
• in 10–20% by 5 years; an annual injection of vitamin B12 should
prevent deficiency in this group

20. 3.Pernicious anaemia
• This is an organ-specific autoimmune disorder
• an incidence of 25/100 000 population
• an average age of onset of 60 years
• Gastric mucosa is atrophic, with loss of parietal cells causing intrinsic
factor deficiency.
• So less than 1% of dietary vitamin B12 is absorbed.
• It is more common in individuals with other autoimmune disease
(Hashimoto’s thyroiditis, Graves’ disease, vitiligo or Addison’s disease)
or a family history of these or pernicious anaemia.

21. Anti IF antibodies
• The finding of anti-intrinsic factor antibodies + macrocytic anaemia
is diagnostic of pernicious anaemia
• present in over 90% of cases but are also present in 20% of normal
females over the age of 60 years
• The Schilling test
• involved measurement of absorption of radio-labelled B12 after oral
administration before and after replacement of intrinsic factor.
• It has become obsolete because of availability of autoantibody tests,
greater caution in the use of radioactive tracers, and limited
availability of IF.

22. 4. Small bowel pathology
a. Pancreatic exocrine insufficiency causes failure to transfer
dietary vitamin B12 from R protein to intrinsic factor.

23. b. Motility disorders or hypogammaglobulinaemia
• can result in bacterial overgrowth, and the ensuing competition for
free vitamin B12 can lead to deficiency.
• This is corrected to some extent by appropriate antibiotics

24. c. Fish tapeworm infestation leads to usurpation of all luminal B12
d. Inflammatory disease of the terminal ileum, such as Crohn’s
disease, TB
e. Surgery of terminal ilium

25. Folate
• Sources
• Leafy vegetables (spinach, broccoli, lettuce )
• Fruits (bananas, melons)
• Animal protein (liver, kidney)
• Minimum daily requirement of 50 μg
• Excess cooking destroys upto 90% of folates

26. Folate absorption
• Dietary folate is polyglutamates
• Converted to monoglutamate in the upper small bowel, absorbed
• Actively transported into plasma
• Plasma folate is loosely bound to plasma proteins such as albumin
and there is an enterohepatic circulation
• Total body stores of folate are small
• Deficiency can occur in a matter of weeks

27. Causes of folate deficiency
1. Diet • poor intake of vegetables/fruits
2. Malabsorption • Coeliac disease , small bowel surgery
3. Increased demand • Cell proliferation in haemolysis • Pregnancy
4. Drugs • Certain anticonvulsants (e.g. phenytoin) • Contraceptive
pill • Certain cytotoxic drugs (e.g. methotrexate)

28. Patient populations prone to Folate deficiency
1. The edentulous elderly.. “ tea and toaster”
2. Psychiatric patients
3. Gut disease or malignancy
4. Pregnant especially twin pregnancies, multiparity ,hyperemesis
5. On haemodialysis
6. Chronic Haemolytic disorders ....Thalassaemics ect
7. Exfolaitive skin diseases….pemphigus,psoriasis

29. Clinical features of megaloblastic anaemia
• Symptoms
 fatigue
 Malaise (90%)
 Breathlessness (50%)
 Paraesthesiae (80%)
 Sore mouth (20%)
 Weight loss
 Impotence
 Poor memory
 Depression
 Personality change
 Hallucinations
 Visual disturbance

30. • Signs
 Smooth tongue
 Angular cheilosis
 Vitiligo
 Skin pigmentation
 Heart failure
 Pyrexia

31. Neurological findings in B12 deficiency
1. Peripheral nerves
• Glove and stocking paraesthesiae
• Loss of ankle reflexes
2. Spinal cord
• Subacute combined degeneration of the cord
• Posterior columns – ↓ vibration sensation and proprioception
• Corticospinal tracts – upper motor neuron signs
3. Cerebrum • Dementia • Optic atrophy
4. Autonomic neuropathy

32. Investigations in megaloblastic anaemia
• Haemoglobin …. Often reduced, may be very low
• MCV .... Usually raised, commonly > 120 fL
• RBC count .…Low for degree of anaemia
• Reticulocyte count …….Low for degree of anaemia
• TLC …. Low or normal
• Platelet count ....Low or normal
• Blood film ….. Oval macrocytosis, poikilocytosis, red cell
fragmentation, neutrophil hypersegmentation

33. Investigations in megaloblastic anaemia
• Serum ferritin……. Elevated
• LDH …… Elevated, often markedly
• Serum B12 levels……
• Serum folate levels…..
• Red cell folate levels…….

34. Investigations in megaloblastic anaemia
• Bone marrow biopsy
• Increased cellularity
• Megaloblastic changes in erythroid series
• Giant metamyelocytes
• Dysplastic megakaryocytes
• Increased iron in stores
• Non -ring sideroblasts

35. Investigation of folic acid deficiency
• Diagnostic findings
• Serum folate levels may be low but are difficult to interpret
• Low red cell folate levels indicate prolonged folate deficiency and are
probably the most relevant measure
• Corroborative findings
• Macrocytic dysplastic blood picture
• Megaloblastic marrow

36. • Serum folate measurement is very sensitive to dietary intake
• a single folate-rich meal can normalise it in a patient with true folate
deficiency
• anorexia, alcohol and anticonvulsant therapy can reduce it in the
absence of megaloblastosis
• Red cell folate levels are a more accurate indicator of folate stores
and tissue folate deficiency

37. Management of megaloblastic anaemia
• Remember Two important points
1. Start Empirical treatment
• If a patient with a severe megaloblastic anaemia is very ill and
treatment must be started before vitamin B12 and red cell folate
results are available
2. Dual supplementation
• treatment should always include both folic acid and vitamin B12.

38. Why dual ?
• The use of folic acid alone in the presence of vitamin B12 deficiency
may result in worsening of neurological features.

39. Need of transfusion
• If IHD or heart failure is present…..give PRBC transfusion
• In elderly and in cd failure ….watch for volume load
• In such circumstances …..slow administration of 1 Unit of red cells
with diuretic cover may be given
• K+ levels can drop in elderly with initiation of treatment ,may cause
cardiac arrythmias. Elderly patients need monitoring and K +
replacement

40. Treatment of B12 deficiency
• Vitamin B12 deficiency is treated with Hydroxycobalamin.
• 1000 μg IM for 6 doses 2 - 3 days apart
• If platelets low…..give iv
• followed by maintenance therapy of 1000 μg every 3 months for life,
• In the presence of neurological involvement, a dose of 1000 μg on
alternate days until there is no further improvement, followed by
maintenance as above, is recommended.

41. Response to therapy
• Reticulocyte count will peak by the Day 5-10
• Haemoglobin will rise by 10 g/L every week until normalised.
• The response of the marrow is associated with a fall in plasma
potassium levels and rapid depletion of iron stores.
• If an initial response is not maintained and the blood film is dimorphic
(i.e. shows a mixture of microcytic and macrocytic cells), the patient
may need additional iron therapy.

42. Response to therapy
• A sensory neuropathy may take 6–12 months to correct;
• long-standing neurological damage may not improve

43. Preparations & doses of Vit B12
1. Hydroxy cobalamin 100, 500, 1000 µg/mL, better retention but can
induce antibody formation ,not used in US. 1 mg every 2 – 3 days 5
doses , then 1 mg 3 monthly
2. Cyanocobalamin: Pink color injection 100 µg/mL .in pernicious
anemia 1000 µg once a week IM for 8 weeks then 1000 µg once a
month life long
3. Methyl cobalamin 0.5 mg tab, Dose 1.5 mg promoted for
neurological defects in diabetics and other peripheral neuropathies

44. Treatment of Folate deficiency
• Oral folic acid (5 mg daily for 3 weeks) will treat acute deficiency and
5 mg once weekly is adequate maintenance therapy.

45. Prophylactic folic acid therapy
1. Prophylactic folic acid in pregnancy prevents megaloblastosis in
women at risk
2. In women of reproductive age it reduces the risk of fetal neural
tube defects
3. Prophylactic supplementation is also given in chronic haemolytic
anaemias , on HD

46. 4. supraphysiological supplementation (400 μg/day) can reduce the
risk of coronary and cerebrovascular disease by lowering plasma
homocysteine levels.
This has led the US FDA to introduce fortification of bread, flour and
rice with folic acid.

47. Some special forms of B12 deficiency
• Acute megaloblastic anemia:
1. Nitrous oxide anesthesia
2. Antifolate drug (eg:trimethoprim, methotrexate)
3. Total parenteral feeding (if without folate)

48. Nitrous oxide anesthesia
• Cobalt is oxidized ,so B12 deficiency occurs over a matter of hours
• Treatment ….parenteral B 12

49. Antifolate drug (eg:trimethoprim, methotrexate)
• Methotrexate toxicity:
• Methotrexate is DHFR inhibitor, its toxicity not reversed by folic acid
• Folinic acid is used as it is an active molecule ,
• There is no need to be reduced by DHFR before it can act,
• Both oral tab and iv forms are available

50. Thanks