Megaloblastic Anaemia

• This is a group of anaemias, usually caused by Vitamin B12 or folate deficiency, characterized by delay in maturation of erythroblast’s nucleus relative to the cytoplasm in

the bone marrow (nuclear cytoplasmic maturation asynchrony)

• Rarely, abnormalities of vit. B12 and folate metabolism or other defects in DNA synthesis may also cause an identical haematological appearance

BIOCHEMICAL BASIS OF MEGALOBLASTIC ANAEMIA

• Dietary folates enter the cells from plasma as methyl THF (a monoglutaminase)
• Vitamin B12 is needed to convert methyl THF to THF, from which polyglutamates forms of folate are synthesized
• Folate, in form of 5,10-methylene tetrahydrofolate (THF) polyglutamate, is required in the synthesis of thymidine monophosphate (dTMP) from its precursor deoxyuridine monophosphate (dUMP), which is a rate limiting step in DNA synthesis

¹¹¹ Tetrahydrofolate                                                

• Nutritional
  • Vegetarian diet
• Malabsorption
  • Gastric causes

 Pernicious anaemia

 Congenital lack of IF^[1]

 Total or partial Gastrectomy

 Abnormal IF – tropic sprue

• Intestinal causes

 Intestinal stagnant loop syndrome – jejunal diverticulosis, blind – loop, structure, etc.

 Chronic tropical sprue  Ileal resection

 Crohn’s disease

 Diphyllobotrum latum (Fish tapeworm) infestation

PERNICIOUS ANAEMIA

• Caused by autoimmune destruction of the parietal cells of the gastric mucosa
• Usually a disease of adults with peak incidence of 60 years
• Females are more affected than males (M:F ratio = 1:1.6)
• There is presence of achlorhydria^[2] with total or near total absence of IF
• Serum gastrin levels are raised
• The disease is common in all races and tend to occur with a familial pattern
• Tendency to develop other autoimmune disorders (e.g. RA^[3], Hashimoto’s thyroiditis, myxedema) is high
• There is also an increased incidence of carcinoma of the stomach (approximately 2-3% of all cases of pernicious anaemia)

Pernicious Anaemia: Associations

• Female
• Blue eyes
• Early greying
• Northern European
• Familial
• Blood group A
• Vitiligo
• Myxedema
• Hashimoto’s disease  Thyrotoxicosis
• Addison’s disease
• Hypoparathyroidism
• Hypogammaglobulinaemia
• Carcinoma of the stomach

CAUSES OF FOLATE DEFICIENCY

• Nutritional
  • Old age
  • Institutions
  • Poverty
  • Famine
  • Special diets
  • Goat’s milk anaemia, etc.
• Malabsorption
  • Tropical sprue
  • Gluten-induced enteropathy
  • Extensive jejunal resection
  • Crohn’s disease
  • Coeliac disease
  • Duodenitis
• Excess urinary folate loss
  • Haemodialysis
  • Active liver dx
  • Congestive heart failure
• Excess utilization
  • Physiological

 Pregnancy and lactation

 Prematurity

• Pathological

 Haemolytic anaemias

 Malignancies – leukaemias, lymphomas, myelomas, carcinomas

 Inflammatory diseases – Crohn’s dx, TB^[4], RA^[5]

• Drugs
  • Anticonvulsants
  • Sulfasalazine
  • Cytotoxic drugs
• Mixed
  • Liver dx
  • Alcoholism
  • Intensive care

PATHOPHYSIOLOGY OF MEGALOBLASTIC ANAEMIA

• The basic abnormality in megaloblastic anaemia is the presence of large number of megaloblasts in the bone marrow
• Megaloblasts are immature erythroblasts with immature nucleus and maturing cytoplasm
• As a result of defective DNA synthesis of BM cells secondary to folate or B12 deficiency, hence the maturation of the nucleus lags behind that of the cytoplasm

(nuclear-cytoplasmic maturation dissociation or asynchrony)

• These megaloblasts are seen as foreign and are destroyed by the BM macrophages
• And so they don’t have the opportunity to differentiate into mature red cells
• Leading to peripheral anaemia (ineffective erythropoiesis)

CLINICAL FEATURE OF MEGALOBLASTIC ANAEMIA

• Insidious onset of signs and symptoms of anaemia
• Mild jaundice resulting from ineffective erythropoiesis
• Purpura resulting from thrombocytopaenia
• Glossitis
• Angular stomatitis
• Weight loss

EFFECTS OF B12 AND FOLATE DEFICIENCY

• Megaloblastic anaemia
• Macrocytosis of epithelial cell surfaces
• Neuropathy (for vitamin B12 only)
• Sterility
• Reversible melanin skin pigmentation (rare)
• Decreased osteoblast activity
• Neural tube defects in the foetus
• Cardiovascular dx, e.g. stroke

LABORATORY FEATURES OF MEGALOBLASTIC ANAEMIA

• Raised MCV
• Oval macrocytes
• Low reticulocyte count
• Moderately low WBC and platelet count
• Hypersegmented neutrophils
• Hypercellular marrow (megaloblasts and giant metamyelocytes are characteristic)
• Serum unconjugated bilirubin and lactate dehydrogenase are raised as a result of marrow cell breakdown

¹¹⁷ PBF – Peripheral Blood Film

• Serum B12 assay
  • Low in B12 deficiency
• Serum and red cell folate assay
  • Low in folate deficiency
• Serum methylmalonic acid and homocysteine levels
  • In B12 deficiency, both are elevated
  • In Folate deficiency, only homocysteine levels are elevated

TESTS FOR THE CAUSE OF VIT. B12 OR FOLATE DEFICIENCY

                                           Vit. B12                                                                  Folate

B12 DEFICIENCY: TREATMENT

• ^[6]IM B12 (Hydroxocobalamin)
  • 1000mcg twice weekly × 3 weeks
  • Then 1000mcg weekly × 1 month
  • Then 1000mcg every 3 months for life for PA^[7] or patients with gastrectomy
• Oral high dose 1-2 mg daily
  • As effective, but less reliable IM
  • Currently only recommended after full parenteral replacement
• Sublingual, nasal spray and gel formulations also available

TREATMENT OF FOLATE DEFICIENCY

• Oral folic acid 5mg daily for 4 months or until haematologic recovery
• Rule out B12 deficiency prior to treatment as folic acid will not prevent progression of neurologic manifestations of B12 deficiency
• Repeat testing for B12 deficiency may be reasonable for those on long-term folic acid therapy if haematologic or neurologic symptoms persist

NON-MEGALOBLASTIC MACROCYTIC ANAEMIAS

• Alcoholism
• Liver dx
• Haemolysis, acute bleeding
• Hypothyroidism
• Aplastic anaemia
• Artifact
  • RBC clumping

 Cold agglutinin dx

• Hyperglycaemia Swelling

ALCOHOLISM

• Common cause of macrocytosis
  • Regular ingestion of 80g of alcohol per day (1 bottle of wine)
  • Abstinence from alcohol leads to resolution of macrocytosis in 2-4 months
• ≈90% of alcoholic have a macrocytosis (100-110 fL) before anaemia develops
• Multifactorial in etiology
  • Direct toxic effect on BM
  • Associated liver dx
  • Reticulocytosis related to GI bleeding
  • Associated folate deficiency

[1] IF – Intrinsic Factor

[2] Absence of stomach acid secretions

[3] RA – Rheumatoid Arthritis

[4] Tuberculosis

[5] Rheumatoid Arthritis

[6] Intramuscular

[7] Pernicious Anaemia, I think.