RED BLOOD CELL DISORDER II

By :Dr Abiodun Mark Akanmode MD.

MACROCYTIC ANEMIAS. All macrocytic anemia are characterized my an MCV

value >100.

Macrocytic anemia can be further classified into megaloblastic and non megaloblastic anemia.

MEGALOBLASTIC ANEMIA. The megaloblastic anemia's are disorders caused by

impaired DNA synthesis.

They are characterized by a distinctive abnormality in the hematopoietic precursors in the bone marrow in which the maturation of the nucleus is delayed relative to that of the cytoplasm.

The underlying defect for the asynchronous maturation of the nucleus is defective DNA synthesis due to deficiency of vitamin B12 (cobalamin) and/or folic acid (folate).

MORPHOLOGY. The presence of red cells that are macrocytic and oval

is highly characteristics of magaloblastic anemia.

Because they are larger than normal and contain ample Hb, most macrocytes lack the central area of pallor.

There is also a marked variation n the size and shape of the red cells.

The neutrophils are larger than normal with their nucleus having 5 or more lobes.

ANEMIA OF VIT B12 DEFICIENCY: PERNICIOUS ANEMIA. Pernicious anemia is a specific form of megaloblastic

anemia caused by autoimmune gastritis and also a failure in production of intrinsic factor which eventually leads to vitamin B12 deff.

2 main auto antibodies are associated with pernicious anemia:

Type I: Blocks binding of Vit B12 to intrinsic factor.

Type II: Prevents the binding of the IF-B12 complex to ileal receptors.

CLINICAL FEATURES OF PERNICIOUS ANEMIA. Pernicious anemia is insidious in onset so the anemia is

often severe by the time the pt seeks help.

Diagnosis is based on:

-Moderate to severe megalobalastic anemia.-Leukopenia with hypersegmented granulocytes.-Low serum Vit B12 levels.-Elevated levels of homocysteine & methylmalonic acid in serum.-Presence of serum antibodies.

NB: Elevated homocysteine levels is a risk factor for atherosclerosis and thrombosis and its suspected that vit B12 deficiency may increase the incidence of vascular disease.

METABOLISM OF VITAMIN B12. Humans are dependant on dietary cobalamin.

Daily requirements of cobalamin is 2-3µg.

A diet of animal product includes large amt of B12 that can last several years.

B12 absorption requires IF, which is secreted by the parietal cells of the fundic mucosa.

Absorbed Vit B12 then makes its way into the liver and other rapidly dividing cells of the body in the bone marrow and GI tract.

BIOCHEMICAL FUNCTION OF B12. Only 2 reaction is humans are known to require B12.

In the first reaction Vit B12 serves as an essential cofactor in the conversion of homocysteine to methionine by methionine synthase.

The other reaction involves the isomerization of methylmalonylcoA to succinyl CoA.

CLINICAL PROBLEMS ASSOCIATED WITH VIT B12 DEFF. Tongue glossitis.

Neurologic diseases:-Peripheral neuropathy with sensorimotor defects.-Sub acute combined degeneration of the spinal cord(SACB)-Dementia from brain involvement.

The schilling’s test has been used to diagnose the cause of Vit B12 deficiency.

ANEMIA OF FOLATE DEFICIENCY. The 3 major causes of folic acid deficiency are:

-Decreased intake.-Increased requirements.-Impaired utilization.

Folic acid is generally abundant in raw foods but very sensitive to heat and are easily destroyed during cooking/frying.

Deficiency of folate is associated with impaired DNA synthesis delays nuclear maturation.

FOLIC ACID METABOLISM

Polyglutamate form is present in green vegetables and animal proteins converted to monoglutamates by intestinal conjugase in the jejunum.

Intestinal conjugase is inhibited by phenytoin.

Monoglutamate is absorbed in the jejunum (active and passive transport).

a. Monoglutamate is converted to methyltetrahydrofolate, the circulating form of folic acid.

b. Absorption of monoglutamate is also blocked by alcohol and oral contraceptives (OCPs).

c. The liver contains only a 3- to 4-month supply of folic acid.

NON-MEGALOBLASTIC MACROCYTOSIS

General differences of non-megaloblastic macrocytosis from megaloblastic macrocytic anemia's include:

a. Macrocytes are round rather than oval or egg-shaped.

b. Hypersegmented neutrophils are not present in the peripheral blood.

c. Leukocytes and platelets are quantitatively normal.

d. Glossitis and neuropathy are absent.

e. Anemia may not be present.

f. Alcohol excess is the most common cause for all types of the macrocytosis.

HEMOLYTIC ANEMIAS Hemolytic anemia's all share the following features:

Premature Rbc destruction(<120days)

Elevated erythropoietin levels and a compensatory increased erythropoesis.

Accumulation of Hb degradation products.

In majority of cases the destruction of Rbc occurs within the phagocyte i.e. Extravacular hemolysis.

Less commonly intravascular hemolysis predominates and its caused by mechanical injury, complement fixation, intracellular parasites etc.

HEMOLYTIC ANEMIA.PATHOGENESIS.

Pathogenesis of hemolytic anemia's:

Intrinsic hemolytic anemia: here there is a defect in the RBC causing the anemia e.g. hereditary spherocytosis, sickle cell anemia,G6PD etc

Extrinsic hemolytic anemia: here factors outside the RBC are responsible for the hemolysis e.g. stenotic aortic valve and immune destruction.

HEMOLYTIC ANEMIA.MECHANISMS.

The 2 major mechanisms responsible for hemolysis include:

Extravascular hemolysis. Intravascular hemolysis.

EXTRAVASCULAR HEMOLYSIS

Premature destruction of red cells within phagocytes of the spleen secondary to the following:

(RBCs are coated by IgG + C3b and macrophages have receptors for IgG and C3b)

Reduced deformability of red cells (abnormally shaped RBCs)

RBCs containing inclusions

Regardless of the cause of extravascular hemolysis, the principal features are:

“ANEMIA, SPLENOMEGALY AND JAUNDICE”

EXTRAVASCULAR HEMOLYSIS

• Maybe decrease in plasma haptoglobin

• Benefit from splenectomy

INTRAVASCULAR HEMOLYSIS

Mechanical damage Enzyme deficiency Complement mediated lysis

Hemoglobinemia, Hemoglobinuria and Hemosiderinuria.

Other features Include anemia & jaundice.

Plasma Haptoglobin is reduced, Serum LDH is elevated

HEREDITARY SPHEROCYTOSIS Intrinsic defect in membrane

RBCs become spheroid, less deformable, vulnerable to splenic sequestration and destruction (Extravascular Hemolysis)

Prevalence is highest in northern Europe (most common intracorpuscular inherited hemolytic anemia in whites)

Autosomal dominant inheritance pattern

PATHOGENESIS

• Life span of RBC ↓10 to 20 days (normal: 120 days)

• Mutations: mostly affect spectrin, ankyrin, band 3,or band 4.2

• After splenectomy - spherocytes persist, but the anemia is corrected

MORPHOLOGY

Spherocytosis

Reticulocytosis Marrow erythroid

hyperplasia Hemosiderosis Mild jaundice

Cholelithiasis (pigment stones) in 40% to 50%

Moderate splenomegaly

OSMOTIC FRAGILITY

Spherocytes are abnormally sensitive to osmotic lysis when incubated in hypotonic salt solutions

CLINICAL FEATURES

Increased MCHC

Anemia, splenomegaly and jaundice

Aplastic crises triggered by parvovirus infection

Hemolytic crises

Symptomatic Gallstones

Splenectomy treats the anemia and its complications (increases risk of sepsis)

OTHER CAUSES OF SPHEROCYTOSIS

Warm Antibody Immunohemolytic Anemias

ABO hemolytic disease of newborn

HEREDITARY ELLIPTOCYTOSIS Autosomal dominant

Mutation in spectrin/band 4.1

Intrinsic defect with extravascular hemolysis

Mild hemolytic anemia

>25% elliptocytes in peripheral blood

GLUCOSE-6-PHOSPHATE DEHYDROGENASE DEFICIENCY

• Most common enzyme deficiency causing hemolysis

• Intrinsic defect with predominantly intravascular hemolysis and mild extravascular hemolysis

• G6PD deficiency: no symptoms until patient is exposed to an environmental factor (infection/drugs) producing oxidants

GLUCOSE-6-PHOSPHATE DEHYDROGENASE DEFICIENCY

• G6PD gene on X chromosome, highest prevalence is in tropical Africa

• G6PD A : 10% of black males in United States (normal enzymatic activity but decreased half-life)

• G6PD Mediterranean - Hemolysis is more severe (half-life of G6PD in this variant is markedly reduced (<10% activity)

GLUCOSE-6-PHOSPHATE DEHYDROGENASE DEFICIENCY

DRUGS : Antimalarials (Primaquine), Sulfonamides, Nitrofurantoin, Phenacetin, Dapsone, Aspirin(in large doses), and Vitamin K derivatives

FAVA beans (in persons of Mediterranean origin)

PATHOGENESIS

Infections induce phagocytes to generate oxidants (e.g. hydrogen peroxide), which are normally stopped up by GSH.

Regeneration of GSH is impaired in G6PD-deficient cells

MORPHOLOGY

Oxidized hemoglobin forms intracellular inclusions called HEINZ BODIES

Splenic phagocytes attempt to “pluck out” Heinz bodies, creating BITE CELLS

RBCs trapped in spleen and destroyed by phagocytes (Extravascular Hemolysis)

CLINICAL FEATURES

Drug-induced hemolysis develops after lag of 2/3 days

RBCs of affected males are uniformly deficient

Marrow compensates by producing new resistant RBCs

PAROXYSMAL NOCTURNAL HEMOGLOBINURIA

Intrinsic defect with intravascular hemolysis

Acquired intracorpuscular defect, X-linked

Somatic mutation in in PIG-A (impaired synthesis of GPI anchor) on MYELOID STEM CELLS

Glycosyl – Phosphatidyl – Inositol (GPI): required for fixation of CD55, CD59 and C8 binding proteins to cell surfaces (protect from complement mediated lysis)

PAROXYSMAL NOCTURNAL HEMOGLOBINURIA

PIG-A deficient precursors produce RBCs sensitive to complement-mediated lysis

All myeloid lineages are affected - Leukocytes are also deficient in protective proteins, but less sensitive to complement mediated lysis than red cells

CLINICAL FEATURES Hemoglobin containing urine on awakening ( NOCTURNAL

because fixation of complement is enhanced by decrease in blood pH during sleep due to CO2 retention)

Iron deficiency possible because of episodic hemoglobinuria

Venous thrombosis (release of aggregating agents from destroyed platelets like adenosine diphosphate)

Increased risk for developing Acute Myeloblastic Leukemia

DIAGNOSIS

Test of Choice : FLOW CYTOMETRY : ↓ CD55/CD59 expression on RBCs, WBCs and platelets

Older Diagnostic Tests: Sucrose Hemolysis Test: sucrose enhances

complement mediated lysis of RBCs Ham Acidified Serum Test: acidified serum activates

the alternative pathway causing hemolysis

TREATMENT

Corticosteroids

Targeted therapy with antibody that prevents the terminal activation of complement components. (ECULIZUMAB)

Anticoagulation to prevent thromboses

Bone marrow transplantation