Hematology 425 Increased RBC Destruction, Intracorpuscular Defects

1. Hematology 425 Increased RBC Destruction, Intracorpuscular Defects Russ Morrison November 1, 2006

2. Intracorpuscular Defects • The RBC membrane consists of 2 interrelated parts • Outer lipid bilayer with integral embedded proteins • Underlying protein membrane skeleton The insoluble lipid outer membrane provides a barrier to separate the different ion and metabolite concentrations of the interior of the RBC from the external environment of the blood plasma

3. Intracorpuscular Defects • The protein skeleton is responsible for shape, structure and deformability of the RBC and contains the pumps and channels for movement of ions and metabolites between the RBC’s interior and the blood plasma • Proteins in the membrane act as receptors, RBC antigens and enzymes • If a review of RBC membrane structure and function is needed, review Chapter 7

4. Intracorpuscular Defects • Genetic defects of RBC membranes have been classified by morphologic features • The two major disorders are • Hereditary spherocytosis (HS), characterized by microspherocytes • Hereditary elliptocytosis (HE), characterized by elliptical RBCs

5. Intracorpuscular Defects • Other RBC membrane disorders are rare and include • Hereditary stomatocytosis (hydrocytosis), characterized by waterlogged RBCs • Hereditary xerocytosis (desiccocytosis), characterized by dehydrated, shrunken RBCs • Hereditary pyropoikilocytosis (HPP), a variant of HE, characterized by bizarrely shaped, shrunken, dehydrated cells that hemolyze when heated to temperatures 2-3oC below the temperature re1quired to hemolyze normal RBCs (49oC)

6. Hereditary Spherocytosis (HS) • HS is a hemolytic anemia characterized by numerous microspherocytes on the PB smear • Described in the late 1800s, associated with the spleen in 1890, and somewhat later with osmotic fragility and reticulocytosis • Incidence is world-wide, but highest in Northern Europeans (1 in 5000 persons) • In caucasians it is the most commonly inherited anemia having an incidence of 220 per million in the US

7. Hereditary Spherocytosis (HS) • Most often inherited as an autosomal dominant expressed in heterozygotes with one affected parent • No homozygotes are known, suggesting death of the fetus may be the result when two HS genes of this type are inherited • In approximately 25% of cases, neither parent has HS, suggesting a recessive form of the disease exists

8. Hereditary Spherocytosis (HS)

9. Hereditary Spherocytosis (HS) • The HS RBC is defective upon its exit from the bone marrow (BM) • Defective RBC's have problems with cellular proteins: spectrin and actin. • 10X more sodium (Na+) enters the cell than normally (glucose powers the ATP shunt that removes Na+). • As the spleen's environment normally deprives the cell of glucose, Na+ levels increase resulting in an accompanying increase of water (to balance the osmolarity) into the cell - may result in bursting.

10. Hereditary Spherocytosis (HS) • Membrane skeletal protein abnormalities cause RBCs to progressively lose unsupported membrane • The RBCs acquire a decreased surface area-to-volume ratio and a spheriodal shape • The RBCs are rigid and not as deformable as a normal RBC • The spleen begins to remove the spherocytes • Exact mechanism of HS RBC destruction is unknown

11. Membrane Layer Separation (HS)

12. Hereditary Spherocytosis (HS) • Clinical and Laboratory Findings • Clinical Presentation • Anemia • Splenomegaly • Intermittent jaundice • Aplastic crises • Megaloblastic crises • Responds well to splenectomy

13. Hereditary Spherocytosis (HS) • Clinical and Laboratory Findings • Laboratory Findings • Reticulocytosis • spherocytosis • Elevated MCHC • Increased osmotic fragility • Normal DAT

14. Hereditary Spherocytosis (HS) In the osmotic fragility test RBCs are placed in hypotonic solutions of varying concentration. The RBC swells forming a near spherical shape. As the RBC expands, the membrane is stretched and the RBC membrane leaks allowing hemoglobin to exit the cell. Equal volumes of blood are placed in a series of hypotonic solutions; allowed to reach equilibrium; centrifuged and the optical density determined. Most normal RBCs remain intact until the % saline reaches about 0.50%. As the % saline decreases further the amount of leakage or lysis increases. This is easily visualized in the osmotic fragility test shown at right. The lower the surface area to volume ratio, the more likely the cell is to lyse. The SA/V is low in hereditary spherocytosis and high in thalassemia.

15. Osmotic Fragility TestNL on top, HS on bottom

16. Direct Antiglobulin Test (DAT) • The direct antiglobulin test looks for antibodies attached to your red blood cells (RBCs). RBCs normally have structures on their surface called antigens. You have your own individual set of antigens on your RBCs, determined by inheritance from your parents. Your plasma cells may produce antibodies to attack these antigens. In addition, some people make antibodies to their own RBCs. These antibodies are produced in autoimmune diseases and are called autoantibodies. In all of these situations, antibodies attach to the RBCs and can result in their destruction.

17. Differential Diagnosis of HS • Family history and evaluation of other family members • Negative DAT rules out immune disorders with spherocytes • The classic laboratory features of HS include minimal or no anemia, reticulocytosis, an increased mean corpuscular hemoglobin concentration (MCHC), spherocytes on the peripheral blood smear, hyperbilirubinemia, and abnormal results on the osmotic fragility test. • Disease may be silent to severe (table 21-1)

18. Treatment and Outcome (HS) • For practical purposes, the treatment of HS involves presplenectomy care, splenectomy, and postsplenectomy complications. • Neonates with severe hyperbilirubinemia caused by HS are at risk for kernicterus, and these infants should be treated with phototherapy and/or exchange transfusion as clinically indicated. • Aplastic crises occasionally can cause the hemoglobin level to fall because of ongoing destruction of spherocytes that is not balanced by new RBC production. Red cell transfusions often are necessary.

19. Treatment and Outcome (HS) • Folic acid is required to sustain erythropoiesis. Patients with HS are instructed to take supplementary folic acid (1 mg/d) for life in order to prevent a megaloblastic crisis. During the first 6 years of life, if patients have compensated anemia, are growing well, and can keep up with their peers in most activities, limiting folic acid supplementation to 1 mg/d is prudent.

20. Treatment and Outcome (HS) • Subsequently, depending on the severity of the disease, splenectomy usually is curative, but not always. Some splenectomies fail because of accessory spleen, accidental autotransplantation of splenic tissue into the peritoneum during surgery, another hemolytic disorder, or splenosis. Failure to observe Howell-Jolly bodies may indicate the presence of functional splenic activity

21. Treatment and Outcome (HS) • Indications for splenectomy are not always clear. • Little doubt exists that patients with more severe anemia and symptoms and complications of HS should undergo splenectomy. Similarly, splenectomy can be deferred safely in patients with mild uncomplicated HS (hemoglobin level >11 g/dL). • No good studies have been performed that provide a basis for clinical judgments in patients with moderate asymptomatic HS (hemoglobin level 8-11 g/dL).

22. Treatment and Outcome (HS) • Splenectomy usually is curative, except in the unusual autosomal recessive variant of HS. • Red cell survival is improved significantly but is not absolutely normal. The MCV usually falls, but the MCHC does not change significantly. Postsplenectomy blood changes include an increased hemoglobin level, decreased reticulocyte count, and the appearance of Howell-Jolly inclusion bodies and target cells. Leukocytosis and thrombocytosis are expected corollaries of splenectomy.

23. Treatment and Outcome (HS) • Fatal sepsis caused by capsulated organisms (eg, Streptococcus pneumoniae, Haemophilus influenzae) is a recognized complication in children who have had a splenectomy. The estimated rate of mortality from sepsis is approximately 200 times greater than that expected in the general population. Although most septic episodes have been observed in children whose spleens were removed in the first years of life, older children and adults also are susceptible. • A simultaneous cholecystectomy in patients with bilirubin stones may eliminate future complications and the need for a second operative procedure.

24. Treatment and Outcome (HS) • Bilirubin gallstones are found in approximately 50% of patients with HS and frequently are present in patients with very mild disease. Therefore, periodic ultrasonic evaluation of the gallbladder should be performed. If surveillance ultrasound examination findings reveal gallstones, performing a prophylactic laparoscopic cholecystectomy seems reasonable. This procedure helps prevent significant biliary tract disease and, in some patients with mild HS, helps avoid the need for splenectomy.

25. Treatment and Outcome (HS) • Children who are candidates for splenectomy include those with severe HS requiring red cell transfusions and those with moderate HS who manifest growth failure or other signs and symptoms of anemia. Splenectomy for children with HS should be performed when the child is older than 6 years.

26. Treatment and Outcome (HS) • Another interesting approach has been the use of partial splenectomy to retain splenic immunologic function while at the same time reducing the rate of hemolysis.

27. Prognosis (HS) • After splenectomy, RBC survival improves dramatically, enabling most patients with HS to maintain a normal hemoglobin level.

28. Hereditary Elliptocytosis (HE) • HE is characterized by the presence of elliptical or oval RBCs on the PB smear • HE was first reported in 1904 • A very heterogeneous disorder clinically, genetically and biochemically • Exists in all forms in 1 in 2000 to 4000 of people in the US in all racial and ethnic groups • Inherited in an autosomal dominant fashion and my be linked to blood group antigens

29. Hereditary Elliptocytosis (HE)

30. Hereditary Elliptocytosis (HE) • HE and its related disorders are caused by mutations that disrupt the red blood cell cytoskeleton, a multiprotein complex responsible for the elasticity and durability of the circulating erythrocytes. Spectrin tetramers form a large part of the skeletal framework and are composed of heterodimers of alpha and beta subunits. These are tethered to the plasma membrane proteins AE1 (band 3) and glycophorin C through the ankyrin/protein 4.2 complex and through protein 4.1R and its associated actin filaments.

31. Hereditary Elliptocytosis (HE) • Mutations that disrupt the formation of spectrin tetramers result in HE. These qualitative defects create a red blood cell membrane that is less tolerant of shear stress and more susceptible to permanent deformation. A few mutations of the alpha-spectrin subunit are responsible for most cases of HE. HE also occurs with deficiencies in protein 4.1 or glycophorin C or when defects of band 3 protein or beta-spectrin impair ankyrin binding.

32. Hereditary Elliptocytosis (HE) • The principal functional consequence of the spectrin mutations is a weakening or disruption of the 2-dimensional integrity of the membrane skeleton. These horizontal membrane defects lead to mechanical instability, which can be sufficient to cause hemolytic anemia with red blood cell fragmentation. How elliptocytes are formed is unclear.

33. Hereditary Elliptocytosis (HE) • Table 21-3 shows the morphologic classification of HE • No treatment is usually required for HE unless hemolytic crises occur • Surgical removal of the spleen may decrease RBC lysis • The majority of individuals with HE have no problems and are unaware of their condition

34. Hereditary Elliptocytosis (HE) • Clinical Presentation • Symptoms • A family history of hereditary elliptocytosis • Prolonged jaundice in the newborn • Jaundice (not in the newborn) • Fatigue • Shortness of breath

35. Hereditary Elliptocytosis (HE) • A CBC (complete blood count) may show anemia and/or cell destruction. • A smear of the blood may show elliptical red blood cells. • Bilirubin may be elevated. • LDH may be elevated. • Cholecystogram (X-ray of gallbladder) may show gallstones.

36. Hereditary Elliptocytosis (HE) • Most cases of HE are caused by membrane instability due to skeletal protein defects • The most common form of HE is “common HE” • Common HE demonstrates several sub-groups including mild common HE, comon HE with chronic hemolysis and common HE with infantile poikilocytosis

37. Hereditary Elliptocytosis (HE) • The second type of HE is a hybrid disorder that combines features of mild HE and mild HS seen in people of northern European origin, called Spherocytic Hereditary Elliptocytosis • The third type of HE is Stomatocytic HE common only in Melanesian and Malaysian populations

38. HE - Stomatocytic

39. Hereditary Pyropoikilocytosis • HPP is a rare disorder that presents in infancy or early childhood as a severe hemolytic anemia with extreme poikilocytosis • Resembles the blood picture of severe burns • May be a subtype of HE • Most victims of the disease are black

40. Hereditary Pyropoikilocytosis • is characterized by an abnormal sensitivity of RBCs to heat • erythrocyte morphology similar to that seen in thermal burns • Patients with HPP tend to experience severe hemolysis and anemia in infancy that gradually improves, evolving toward typical ellyptocytosis later in life. • HPP has been associated with a defect of the erythrocyte membrane protein spectrin and with spectrin deficiency

41. Hereditary Pyropoikilocytosis

42. Additional Intracorpuscular Defects • Still to discuss – next time • Inherited disorders of RBC cation permeability and volume • RBC enzymopathies (selected) • PNH