Title: Hematology 425 Increased RBC Destruction, Intracorpuscular Defects
1Hematology 425 Increased RBC Destruction,
Intracorpuscular Defects
- Russ Morrison
- November 1, 2006
2Intracorpuscular 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
3Intracorpuscular 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 RBCs 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
4Intracorpuscular 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
5Intracorpuscular 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)
6Hereditary 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
7Hereditary 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
8Hereditary Spherocytosis (HS)
9Hereditary 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.
10Hereditary 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
11Membrane Layer Separation (HS)
12Hereditary Spherocytosis (HS)
- Clinical and Laboratory Findings
- Clinical Presentation
- Anemia
- Splenomegaly
- Intermittent jaundice
- Aplastic crises
- Megaloblastic crises
- Responds well to splenectomy
13Hereditary Spherocytosis (HS)
- Clinical and Laboratory Findings
- Laboratory Findings
- Reticulocytosis
- spherocytosis
- Elevated MCHC
- Increased osmotic fragility
- Normal DAT
14Hereditary 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.
15Osmotic Fragility TestNL on top, HS on bottom
16Direct 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.
17Differential 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)
18Treatment 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.
19Treatment 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.
20Treatment 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
21Treatment 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 gt11
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).
22Treatment 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.
23Treatment 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.
24Treatment 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.
25Treatment 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.
26Treatment 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.
27Prognosis (HS)
- After splenectomy, RBC survival improves
dramatically, enabling most patients with HS to
maintain a normal hemoglobin level.
28Hereditary 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
29Hereditary Elliptocytosis (HE)
30Hereditary 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.
31Hereditary 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.
32Hereditary 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.
33Hereditary 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
34Hereditary 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
35Hereditary 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.
36Hereditary 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
37Hereditary 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
38HE - Stomatocytic
39Hereditary 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
40Hereditary 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
41Hereditary Pyropoikilocytosis
42Additional Intracorpuscular Defects
- Still to discuss next time
- Inherited disorders of RBC cation permeability
and volume - RBC enzymopathies (selected)
- PNH