Coagulation: In medicine, the clotting of blood. The process by which the blood clots to form solid masses, or clots. More than 30 types of cells and substances in blood affect clotting. The process is initiated by blood platelets. Platelets produce a substance that combines with calcium ions in the blood to form thromboplastin, which in turn converts the protein prothrombin into thrombin in a complex series of reactions. Thrombin, a proteolytic enzyme, converts fibrinogen, a protein substance, into fibrin, an insoluble protein that forms an intricate network of minute threadlike structures called fibrils and causes the blood plasma to gel. The blood cells and plasma are enmeshed in the network of fibrils to form the clot.

1. Lecture
4
Disorders
of
Primary
Hemostasis:
Quan7ta7ve
Platelet
Disorders
1

2. Disorders
of
Primary
Hemostasis
• Abnormali7es
that
result
in
bleeding
due
to
defects
in
forma7on
of
the
primary
hemosta7c
(platelet)
plug
• Defect
in
the
ability
of
platelets
to
adhere
to
the
vascular
endothelium
– Platelet
aggrega7on
is
normal
• Defects
in
primary
hemostasis
are
classified
as
– Qualita7ve
defects
– Quan7ta7ve
defects
• Present
as
– Acquired
defects
• Bleeding
episodes
usually
do
NOT
present
un7l
adulthood
– Congenital
defects
• Bleeding
episodes
present
during
early
childhood
• Purpura—refers
to
petechiae
and
ecchymoses
• Easy
bruisability—too
many
petechiae
and
ecchymoses—less
than
“usual”
trauma
• Excess
bleeding—Involves
both
platelets
and
coagula7on
abnormali7es
2

3. Clinical
Manifesta7ons
• Petechiae
– Small
red
to
purple
spots
in
the
skin,
[<3
mm]
– Blood
leaking
from
the
endothelial
capillary
lining
– Occur
on
the
extremi7es
due
to
high
venous
pressure
– Manifest
as
platelet
and
blood
vessel
abnormali7es
• Ecchymoses
– Bruises
[>3
mm]
– Caused
by
blood
escaping
through
the
endothelium
and
into
intact
subcutaneous
7ssue
—come
from
vessels
larger
than
a
capillaries
– Red
to
purple
ini7ally
à
turn
yellowish
green
as
they
heal
– Found
in
defects
involving
blood
vessels,
platelet,
and
coagula7on
proteins
• Hematoma
– Blood
leaks
from
a
vessel
and
collects
in
the
intact
skin
– Blue
or
purple
and
slightly
raised
– Can
occur
in
organs
and
7ssues
– May
be
in
the
form
of
a
clot
3

4. Quan7ta7ve
Platelet
Disorders
• Thrombocytopenia
– Clinical
symptoms
typically
not
seen
un7l
<100
X
109/L
• More
o"en
<50
X
109/L
• Spontaneous
bleeding
occurs
<20
X
109/L
• Life-­‐threatening
<10
X
109/L
– Clinical
Manifesta7on
Ø Petechiae
Ø Menorrhagia
Ø Spontaneous
bruising
Ø Fatal
bleeding
into
the
CNS
may
occur
Ø Spontaneous
bleeding
in
GI-­‐tract,
GU-­‐tract
and
nose
Ø Prolonged
BT
but
Normal
coagula.on
tests
• Due
to
1. Deficient
platelet
producCon
2. Abnormal
platelet
distribuCon
(splenic
sequestraCon)
3. Increased
destrucCon
• Secondary
to
an
underlying
disease
• Most
common
cause
of
excess
or
abnormal
bleeding
4

5. Mechanisms
of
Thrombocytopenia
1. Decreased
Produc7on
A. Megakaryocy7c
hypoplasia
B. Replacement
of
normal
marrow
Ø Tumor
cells
(Myelophthisic
picture)
Ø Fibrosis
C. Ineffec7ve
thrombopoiesis
2. Abnormal
Platelet
Distribu7on
A. Dilu7onal
thrombo-­‐
cytopenia
B. Increased
splenic
sequestra7on
3. Increased
Destruc7on
A. Immune
B. Nonimmune
5

6. Mechanism
of
Destruc7on
• Immunologic
causes
– Alloan7bodies
– Autoan7bodies
– Drug-­‐induced
an7bodies
– Isoan7bodies
• Non-­‐immunologic
causes
– DIC
– TTP
– HUS
– Microangiopathy
– Vasculi7s
more
frequently
6
Immune-­‐mediated
causes
occur
1. Result
in
hemorrhagic
diathesis
2. Presence
of
schistocytes

7. Immune-­‐Mediated
Destruc7on
• Group
of
thrombocytopenias
in
which
an
immune-­‐mediated
mechanism
causes
increased
destruc7on
of
platelets
• Two
types
immune-­‐mediated
destrucCon
1. Primary
(Idiopathic)
– Defects
that
are
intrinsic
to
the
platelet
2. Secondary
– Defect
that
is
extrinsic
to
the
platelet
Ø Due
to
an
underlying
disease
7

8. Immune
Mediated
Destruc7on
• Caused
by
anCbodies
–
analogous
to
immune-­‐
mediated
destruc7on
of
RBC’s
• Platelets
become
sensi7zed
with
an7body
• Mononuclear
phagocytes
destroy
these
an7body-­‐
coated
platelets
in
the
spleen
• Monocytes
(macrophages)
have
Fc
receptors
that
they
use
to
recognize
à
platelets
that
are
coated
with
an7body
– Leads
to
decreased
survival
7me
in
circula7on
(2-­‐3
days)
• An7bodies
abach
to
platelets
by
their
Fab
regions
to
either
1. GPIIb/IIIa
2. GPIb/IX
3. Nonspecifically
to
immune
complexes
via
FcγRIIA
• Monocytes
recognize
platelets
coated
with
IgG,
IgM,
IgA,
and
complement
8

9. Immune
Thrombocytopenia
Immune
Thrombocytopenic
Purpura—ITP
• ITP
(autoimmune
thrombocytopenia)
–
autoimmune
disorder
characterized
by
• (1)
Immune-­‐mediated
destrucCon
of
platelets
• (2)
impaired
platelet
producCon
• Autoan7bodies
–
mostly
IgG
–
directed
against
GPIIb/IIIa,
GPIb/IX,
GPV
• One
of
the
most
common
disorders
causing
severe
isolated
thrombocytopenia
– Most
cases
à
asymptoma7c
– Low
platelet
counts
can
lead
to
a
bleeding
diathesis
and
purpura
– There
is
no
specific
test
that
readily
confirms
the
diagnosis
of
ITP
à
therefore
it
is
a
diagnosis
of
exclusion
– An7platelet
an7bodies
+
BM
examina7on
+
Clinical
presenta7on
• Two
types
ITP
1. Acute
ITP
2. Chronic
ITP
• 50-­‐100
new
cases
per
million
per
year,
with
children
accoun7ng
for
half
of
that
amount
• Clinical
features
Ø Bruising,
Petechiae,
Epistaxis,
Gingival
bleeding
Ø Thrombocytopenia
(platelet
count
is
below
30,000)
Ø hbp://www.itpscience.com/regula7on_platelet_produc7on/itp_video.html
9

10. Pathology
of
ITP
1. A
trigger
for
platelet
destruc7on
is
the
produc7on
of
ITP
autoanCbodies
2. An7bodies
to
the
platelet
glycoprotein
IIb/IIIa
complex
bind
to
platelets
and
leading
to
phagocytosis
by
re7culo-­‐
endothelial
macrophages
via
Fc
receptors
3. The
platelet
proteins
are
degraded
and
displayed
on
the
macrophage
cell
surface
in
a
complex
with
CD154
• CD154
=
CD40
LIGAND
à
it
binds
to
CD40
on
APCs
4. Macrophages
à
s7mulate
T-­‐cell–
mediated
an7body
produc7on
by
B
cells
5. The
resul7ng
autoanCbodies
perpetuate
platelet
destrucCon

11. Acute
ITP
• E7ology
– Post-­‐viral
infec7on
in
children
1-­‐7
years
of
age
– Generally
lasts
<6
months
– Affects
males
and
females
equally
• Pathophysiology
– Commonly
preceded
by
a
previous
viral
infec7on
or
immuniza7on
• HIV,
rubella,
rubeola,
varicella,
mumps,
EBV,
and
CMV
1. [An.bodies/an.body
complexes]
are
produced
during
viral
infecCon
and
they
complexes
abach
to
the
platelet
surface
2. The
[platelet
+
an7body
complexes]
are
removed
by
macrophages
in
spleen
3. Autoan7bodies
are
produced
against
ABs
directed
against
viral
or
bacterial
an7gens
that
cross-­‐react
with
platelets
a. Autoan7bodies
result
from
the
persistence
of
pro-­‐inflammatory
cytokines
and
the
s7mulated
T-­‐cell
response
à
following
a
viral
or
environmental
trigger
b. This
s.mulated
response
leads
to
the
emergence
of
previously
suppressed
autoanCbodies
• Key
pathology—failure
to
suppress
these
autoanCbodies
a. May
be
caused
by
CD25+
T-­‐regulatory
cells
which
are
not
fully
mature
in
young
children
à
therefore
these
autoan7bodies
are
produced
11

12. Chronic
ITP
• E7ology
– Unknown;
adults
20
-­‐
50
years
of
age
– Insidious
onset
with
lack
of
a
previous
vial
infec7on
– Female-­‐to-­‐male
ra7o
=
1.7:1
– Median
age
38-­‐49
– Spontaneous
remission
is
uncommon
– Persistent
thrombocytopenia
las7ng
more
than
6-­‐12
months
to
years
– An7platelet
an7bodies
found
in
58-­‐80%
of
pa7ents
• Signs
and
Symptoms
– Petechiae,
ecchymoses,
epistaxis,
menorrhagia,
gingival
bleeding,
hematuria,
absence
of
splenomegaly
– Treat
if
platelet
count
drops
<30,000
• Pathophysiology
– Autoan7bodies
(IgG)
produced
against
platelet
an7gens
à
platelet-­‐an7body
complexes
removed
by
macrophages
in
spleen
– Helicobacter
pylori
infec7ons
have
been
suggested
to
be
involved
in
chronic
ITP
• 43-­‐75%
of
pa7ents
with
chronic
ITP
have
H.
pylori
à
eradica.on
of
H.
pylori
with
an.bio.cs
improves
situa.on
12

13. Comparison
of
Acute
versus
Chronic
ITP
Feature
Acute
ITP
Chronic
ITP
Peak
age
Children
–
2-­‐4
years
Adults
–
20-­‐40
years
Platelet
count
(ini7al)
<20
x
109/L
30-­‐80
x
109/L
Onset
Abrupt
Insidious
Antecedent
infec7on
Common
–
1-­‐3
weeks
Unusual
Spontaneous
remission
~93%
of
cases
Rare
Course
of
disease
fluctuates
Therapy
1. Cor7costeroids
2. An7-­‐D
3. IVIg
1. Cor7costeroids
2. Splenectomy
13

14. Laboratory
Findings
in
ITP
Peripheral
blood
1. Decreased
platelet
count
on
peripheral
blood
smear
2. Megathrombocytes
(large
platelets)
on
peripheral
blood
smear
3. Other
CBC
parameters
within
reference
range
Bone
marrow
1. Megakaryocytes
are
normal
to
increased
in
the
bone
marrow
– Autoan7bodies
may
interfere
with
platelet
produc7on
or
platelet
release
from
the
bone
marrow
– Suppression
of
megakaryocyte
produc7on
by
autoan7bodies
may
be
associated
with
increased
apoptosis
in
adult
ITP
(ineffec7ve
thrombopoiesis)
2. Thrombopoie7n
levels
are
normal
or
slightly
increased
in
some
ITP
pa7ents
resul7ng
in
normal
to
increased
megakaryocytes
14

15. Lab
Findings
in
ITP
15
Normal
PB
Bone
Marrow
ITP
PB
Petechiae
Purpura

16. Treatment
of
ITP
• Treatment
– When
PLTs
<30
x
109/L
• Steroid
therapy;
if
ineffec7ve
• Intravenous
an7-­‐D
(in
Rh
posi7ve
pa7ents)
– Interacts
with
the
an7body-­‐coated
RBCs
–
the
macrophages
are
busy
destroying
RBCs
and
leave
the
platelets
alone
–
hemolysis
is
common
• IVIG
– Saturates
the
Fc
receptors
on
macrophages
blocking
them
from
binding
to
AB-­‐coated
platelets
• Splenectomy
in
pa7ents
refractory
to
the
above
• Platelet
transfusion
if
severe
hemorrhage
– Cor7costeroids
are
the
treatment
of
choice
– Followed
by
splenectomy
if
refractory
to
cor7costeroids
– Newer
therapies
• An7CD20+
(Rituximab)
• An7-­‐CD40+
16

17. Regula7on
of
Platelet
Produc7on
• TPO
is
produced
in
the
liver
• Inflamma7on
and
thrombocytopenia
enhance
TPO
produc7on
• Platelets
have
high
affinity
TPO
receptors
and
remove
TPO
from
the
circula7on
• Free
plasma
thrombopoie7n
binds
to
megakaryocytes
à
s.mula.on
of
megakaryocytopoiesis
The molecular mechansims that control hematopoesis. JCI. 2005.

18. Thrombopoie7n-­‐Receptor
Agonists
for
Primary
Immune
Thrombocytopenia
NEJM.
2011
• Eltrombopag
– Oral
thrombopoie7n
(TPO)
receptor
agonist
– Interacts
with
transmembrane
domain
of
human
TPO
receptor
– Induces
megakaryocyte
prolifera7on
and
differen7a7on
from
bone
marrow
progenitor
cells
• Romiplos7m
– An
Fc-­‐pep7de
fusion
protein
(pep7body)
– Increases
platelet
produc7on
through
binding
and
ac7va7on
of
the
thrombopoie7n
(TPO)
receptor
–
similar
mechanism
to
endogenous
TPO
18

19. Other
Causes
of
Thrombocytopenia
• ITP
in
Pregnancy
– Gesta7onal
thrombocytopenia
– Benign
condi7on
• Platelet
count
returns
to
normal
within
12
weeks
post-­‐delivery
• If
the
diagnosis
is
made
during
pregnancy
à
IVIG
and
steroid
therapy
may
be
used
• An7body-­‐related
platelet
destruc7on
occurs
in
females
previously
immunized
–most
pa7ents
are
mul7parous
• An7bodies
are
directed
against
platelet
an7gen
PLA-­‐1A
(HPA-­‐1a)
• Post-­‐Transfusion
Purpura
– Rare
form
of
alloimmune
thrombocytopenia
characterized
by
severe
thrombocytopenia
and
bleeding
à
following
TRANSFUSION
of
blood
or
blood
products
– Caused
by
anCbody-­‐related
platelet
destrucCon
in
previously-­‐immunized
pa7ents
– An7bodies
are
directed
against
platelet
an7gen
PLA-­‐1a
(HPA-­‐1a)
in
most
cases
– Severe
thrombocytopenia
occurs
~3-­‐12
days
following
transfusion
– Diagnosis
of
PTP
made
by
detec;ng
an;bodies
against
platelet-­‐specific
an;gens
in
the
pa;ent’s
serum
19

20. Other
Causes
of
Thrombocytopenia
• Neonatal
Alloimmune
Thrombocytopenia
(NAITP)
– Caused
by
fetal-­‐maternal
incompa7bility
of
platelet
an7gens
– Maternal
an7bodies
cross
the
placenta
causing
destruc7on
of
the
fetal
platelets
– First
pregnancy
affects
50%
of
cases
– Offending
an7body
is
an7-­‐HPA-­‐1a
and
is
an
IgG
alloan7body
(75%
of
cases)
• These
are
also
directed
against
gpIIb/IIIa,
Ib/IX,
Ia/IIa,
and
CD109
• In
whites
97.5%
of
the
an7bodies
are
against
gpIIb/IIIa
– Affected
neonate
is
treated
by
transfusion
of
an7gen-­‐compa7ble
platelets
or
washed
maternal
platelets
• Congenital
MegakaryocyCc
Hypoplasia
– Decrease
in
bone
marrow
megakaryocytes
1. Thrombocytopenia
with
Absent
Radii
(TAR)
2. Wiskob-­‐Aldrich
Syndrome
(WAS)
3. May-­‐Hegglin
Anomaly
(MHA)
20

21. Thrombocytopenia
Due
to
Impaired
Platelet
Produc7on
• Thrombocytopenia
with
absent
radii
(TAR)
– Characterized
by
A. Neonatal
thrombocytopenia
and
B. Hypoplasia
of
the
radial
bones
of
the
forearms
with
absent,
short,
or
malformed
ulnae
1. Impaired
DNA
repair
that
results
from
a
fetal
injury
about
8
weeks
gesta7on
2. Pa7ents
have
90%
incidence
of
leukemoid
reac7ons
with
WBC
counts
exceeding
100,000/
μL
3. Platelet
counts
range
from
10,000-­‐30,000/μL
4. A
failure
in
produc7on
of
humoral
or
cellular
s7mulators
of
mega-­‐
karyocytopoiesis
21

22. May-­‐Hegglin
Anomaly
• Characterized
by
various
degrees
of
thrombocytopenia
• May
be
associated
with
1. Purpura
and
bleeding
2. Giant
platelets
(20
μm
in
diameter)
containing
few
granules
3. Large
(2-­‐5
μm
basophilic
cytoplasmic
inclusion
bodies
in
granulocytes
that
resemble
Döhle
bodies
• Otherwise
normal
platelet
morphology
and
func7on
• Muta7on
in
the
MYH9
gene
present
in
chromosomal
22
– A
cytoskeletal
protein
in
platelets
that
may
be
responsible
for
the
abnormal
platelet
diameter
• Most
pa7ents
have
no
bleeding
episodes
unless
thrombocytopenia
is
severe
22

23. Wiskob-­‐Aldrich
Syndrome
• Wiskob-­‐Aldrich
syndrome
is
an
immune
deficiency
disorder
in
which
there
is
a
decreased
produc7on
of
IgM
•
WAS
is
characterized
by
1. Thrombocytopenia
with
small
platelets
(microthrombocytes)
2. Eczema
3. Increased
risk
of
developing
an
autoimmune
disorder
or
cancer
4. Associated
with
a
defec7ve
gene
on
the
X
chromosome
• Females
tend
to
be
carriers
of
the
syndrome
• Males
have
the
defec7ve
gene
and
develop
symptoms
• X-­‐linked
mode
of
transmission
– DefecCve
protein
called
WASp
(Wiskod-­‐Aldrich
syndrome
protein)
whose
expression
is
limited
to
cells
of
hematopoie7c
lineage
23

24. Thrombocytopenia
due
to
Ineffec7ve
Thrombopoiesis
• Associated
with
normal
to
increased
marrow
cellularity
but
peripheral
blood
cytopenias
1. Megaloblas7c
anemia
à
associated
with
a. Vitamin
B12
or
folate
deficiency
b. Thrombocytopenia
results
from
impaired
DNA
synthesis
c. Lactate
dehydrogenase
(LD)
levels
are
elevated
due
to
intra-­‐
medullary
death
of
hematopoie7c
progenitors
2. Myelodysplas7c
syndromes
may
simulate
vitamin
deficiency
and
do
not
respond
to
vitamin
replacement
therapy
3. Alcohol
has
direct
toxic
effect
on
the
marrow
à
induces
folic
acid
and/or
vitamin
B12
deficiency
• Thrombocytopenia
is
mild
with
normal
platelet
life
span
24

25. Drug-­‐Induced
Thrombocytopenia
• Rela7vely
common—more
than
200
drugs
have
been
reported
• hbp://w3.ouhsc.edu/platelets
• Symptoms
6-­‐7
days
azer
administra7on
• Platelet
count
is
extremely
low
(<10
x109/L)
• Petechiae,
purpura,
and
occasionally
intracranial
bleeding
• Treatment
involves
removal
of
the
offending
drug
• Three
pathways
to
explains
drug-­‐induced
immune-­‐mediated
platelet
destruc7on
1. Hapten
theory
• Small
molecule
that
can
elicit
an
immune
response
ONLY
when
abached
to
a
large
carrier
protein
• The
drug
(carrier
protein)
binds
covalently
to
platelets
à
[drug-­‐platelet
anCgenic
complex]
-­‐-­‐
the
drug
acts
as
a
hapten
2. Innocent
bystander
mechanism
• The
drug
binds
to
a
specific
anCbody
and
elicits
an
immune
response
• An7body
binding
to
the
[drug-­‐protein
complex
]forms
an
immune
complex
that
nonspecifically
binds
to
circula7ng
platelet
Fc
receptors
3. Drug-­‐dependent
anCbodies
• An7bodies
are
created
against
an
epitope(s)
created
by
the
associaCon
of
the
drug
with
proteins
on
the
platelet
surface
25

26. Hapten
Theory
• Small
molecule
that
can
elicit
an
immune
response
ONLY
when
abached
to
a
large
carrier
protein
• The
drug
(carrier
protein)
binds
covalently
to
platelets
à
[drug-­‐platelet
anCgenic
complex]
-­‐-­‐
the
drug
acts
as
a
hapten
hbp://classes.midlandstech.edu/carterp/Courses/bio225/
chap19/19-­‐05_Thrombocyto_1.jpg26

27. Varia7ons
in
An7body
Binding
to
Platelets
• A—Platelet
autoan7bodies
or
allo-­‐
an7bodies
– Bind
to
epitopes
of
GPIIb/IIIa,
GPIb/
IX
• B—Quinine/Quinidine-­‐dependent
an7bodies
– Bind
to
a
complex
of
drug
and
glycoprotein
– GPIIb/IIIa
or
GPIb/IX
• C—Heparin-­‐dependent
an7bodies
– Heparin
binds
to
PF4
and
the
heparin:PF4
complex
binds
to
IgG
an7heparin
an7bodies
via
the
Fab
of
the
an7body
– The
Fc
por7on
of
the
an7body
binds
to
platelet
IgG
FCγIIa
receptors
27

28. Condi7ons
with
Mul7ple
Mechanism
of
Thrombocytopenia
28
Alcoholism
1. In
alcoholic
pa7ents
without
cirrhosis
the
major
effect
is
ethanol.
a. Ethanol
directly
suppresses
MGK
producCon.
b. Causes
folate
deficiency.
2. In
pa7ents
with
cirrhosis
the
major
effect
is
due
to
under
produc7on
of
coagula7on
factors
by
the
liver.
1. Suppress
platelet
produc7on
2. Ineffec7ve
platelet
produc7on
3. Increased
destruc7on
4. Splenomegaly
Lymphoprolifera7ve
Disease
1. Impaired
produc7on
2. Immune
destruc7on
3. Splenomegaly
Cardiopulmonary
Bypass
Surgery
1. Mechanical
destruc7on
2. Increased
u7liza7on
3. Dilu7onal
thrombocytopenia
• 10
or
more
units
of
blood
4. Inadequate
neutraliza7on
of
heparin

29. Thrombo7c
Microangiopathies
(TMA)
• Group
of
disorders
characterized
by
– Microangiopathic
hemoly7c
anemia
– Thrombocytopenia
– Microvascular
thrombosis
• Subtypes
TMA
– Thrombo7c
thrombocytopenic
purpura
(TTP)
– Hemoly7c
uremic
syndrome
(HUS)
29
End
organ
damage

30. Thrombo7c
Thrombocytopenic
Purpura
• Congenital
–
Upshaw-­‐Shulman
syndrome
– Characterized
by
repeated
episodes
of
thrombocytopenia
and
microangiopathic
hemoly7c
anemia
during
early
childhood
– Moake
(1982)
described
unusually
large
vWF
mul7mers
in
the
plasma
of
pa7ents
with
TTP
• Proposed
that
a
lack
of
a
“cleaving
protease”
was
responsible
• Congenital
deficiency
of
ADAMTS-­‐13
–
disintegrin-­‐like
and
metalloprotease
with
thrombospondin
type
1
mo.f
30
Brass, L, 2001, Nature Med 7:1177-1178.

31. Thrombo7c
Thrombocytopenic
Purpura
• Acquired
–
Idiopathic
TTP
– Involves
an
autoimmune
mechanism
à
acquired
absence
of
ADAMTS13
ac7vity
– Usually
associated
with
autoan7body
–
IgG
inhibitor
of
the
protease
– Extremely
rare
in
pa7ents
without
a
thrombo7c
microangiopathy
• With
the
possible
excep.on
of
sepsis
• Secondary
TTP
– Mechanisms
poorly
understood
–>
levels
of
ADAMTS13
ac7vity
generally
not
as
depressed
as
in
idiopathic
– Comprises
~40%
of
cases
of
TTP
– Predisposing
factors
• Cancer
• BMT
• Pregnancy
• Medica7ons
• HIV
infec7on
31

32. vWF
• Large
mul7meric
protein
–
ranges
from
600
kD
to
>
20
million
kD
– Synthesized
by
endothelial
cells
and
megakaryocytes
• Endothelial
cells
source
of
plasma
vWF
– Released
from
the
endothelial
cells
as
mature
vWF
azer
cleavage
of
a
propep7de
– vWF-­‐cleaving
protease
cleaves
the
ULvWF
into
inac7ve
monomers
to
prevent
interac7on
with
platelets
• Func7on
of
vWF
1. Supports
platelet
adhesion
and
ac7va7on
at
sites
of
vascular
injury:
a. vWF
binds
extravascular
collagen
b. Platelets
adhere
to
bound
vWF
2. Supports
coagula7on
mechanism:
a. vWF
protects
FVIII
in
circula7on
b. vWF
co-­‐localizes
FVIII
at
sites
of
vascular
injury
32
Platelets
Coagula7on
Proteins
Endothelium
vWF

33. Synthesis
of
vWF
• Steps
in
synthesis
of
vWF
1. First
synthesized
as
a
pro-­‐vWF
monomer
2. Dimeriza.on
occurs
in
ER
3. Pro-­‐vWF
monomers
linked
together
at
the
carboxyl
terminal
end
4. Dimeric
molecules
pass
to
the
Golgi
apparatus
5. Dimers
mul.merize
6. Propep7de
is
cleaved
off
à
mature
subunit
33
Blood
79:2507
Prog
Heamtol
9:233

34. Func7on
of
ADAMTS
13
• ADAMTS-­‐13
abaches
to
binding
sites
on
the
endothelial
cell
surfaces
– ADAMTS-­‐13
abaches
to
endothelial
surface
via
à
a
thrombospondin-­‐1-­‐
like
domain
–
RGD
(arginine/glycine/aspartate)
• Cleaves
ULvWF
as
they
are
secreted
by
the
s7mulated
endothelial
cells
• Smaller
vWF
forms
that
circulate
azer
cleavage
do
not
induce
the
adhesion
and
aggrega7on
of
platelets
during
normal
blood
flow

35. Func7on
of
ADAMTS
13
35
• Absent
or
severely
reduced
ac7vity
of
ADAMTS-­‐13
prevents
cleavage
of
ULvWF
as
they
are
secreted
by
endothelial
cells
• The
uncleaved
mul.mers
induce
adhesion
and
aggrega7on
of
platelets
in
flowing
blood
• Due
to:
– Congenital
or
acquired
deficiency
of
ADAMTS-­‐13
• Note:
– Interference
with
the
aWachment
of
ADAMTS-­‐13
to
endothelial
cells
in
vivo
à
may
also
cause
TTP
in
pa.ents
with
normal
ADAMTS-­‐13
ac.vity
in
plasma

36. Pathology
of
TTP
• Classic
pentad
of
features
1. Microangiopathic
hemoly7c
anemia
2. Thrombocytopenia
3. Neurologic
symptoms
4. Kidney
failure
5. Fever
• Affects
kidneys,
heart,
and
brain
with
small
arteriolar
thrombi
• TTP
overlaps
with
hemoly7c
uremic
syndrome
(HUS)
that
may
be
precipitated
by
verotoxins
from
such
organisms
as
E.
coli
(type
O157:H7)
à
endothelial
injury
hbp://library.med.utah.edu/WebPath/RENAHTML/RENAL030.html
Glomerulus
BV
with
onion-­‐skinning
(thromboCc
microangiopathy)
Curr
Opin
Nephrol
Hypertens
19
(3):
242-­‐7

37. Hemoly7c
Uremic
Syndrome—HUS
• Thrombo7c
microangiopathy
that
mainly
affects
children
• Characterized
by
a
Tetrad
of
clinical
findings
1. Hemoly.c
anemia
with
RBC
fragmenta.on
2. Acute
renal
failure
3. Thrombocytopenia
4. Variable
CNS
involvement
• Associated
with
a. Upper
respiratory
infec.on
b. Urinary
tract
infec.on
c. Viral
disease
such
as
varicella
or
measles
• Generally
encompasses
several
diverse
disorders
– Typical
form
1. Associated
with
diarrhea
caused
by
verotoxin-­‐producing
E.
coli
– ~95%
of
all
cases
in
children
2. Most
none-­‐sporadic
cases
in
adults
– Atypical
form
• Exhibit
autosomal
dominant
or
recessive
inheritance
• Associated
with
deficiencies
in
proteins
that
regulate
the
alterna7ve
pathway
of
complement
ac7va7on
• Adult-­‐onset
HUS
– Primary—no
iden7fiable
cause
– Secondary—associated
with
• Bacterial
infec7ons—classic
HUS
• ConnecCve
Cssue
diseases—SLE,
Marfan
syndrome,
Ehlers-­‐Danlos
syndrome
• Cancer
à
stomach,
colon,
breast
37

38. Diagnosis
•
Diarrhea
(ozen
bloody)
•
Hematological
• Microangiopathic
haemoly7c
anemia
• Thrombocytopenia
Fragmented
red
cells
Absence
of
platelets
ACUTE
KIDNEY
INJURY

39. Mechanism
of
Ac7on
in
Typical
HUS
• Subdivided
into
2
groups
1. Bloody
diarrheal
prodrome
(+)
2. Bloody
diarrheal
prodrome
(-­‐)
Ø Diarrhea-­‐related
(classic)—(D+)HUS
1. E.
coli
O157:H7
• Found
in
GI
tract
of
cable
• Majority
of
human
infec7ons
traced
to
inges7on
of
incompletely
cooked
beef
contaminated
with
the
organism
• Associated
with
verocytotoxin
(shiga-­‐like
toxin
I
and
II)
produced
during
E.
coli
infec7on
2. S.
dysenteriae
serotype
I
• Produces
Shiga
toxin
Ø Non-­‐diarrhea-­‐associated—(D—)-­‐HUS
– Reported
in
both
children
and
adults
– Sporadic
disease
NOT
preceded
by
diarrhea
– Endemic
HUS
80-­‐90%
cases
39
10%
cases

40. Proposed
Mechanism
Platelet-­‐Fibrin
Forma7on
in
“Classic”
HUS
1. Shiga
toxin
binds
to
Gb3
receptor
on
EC’s
– Local
damage
to
colon
mucosa
2. Shiga
toxin
enters
circula.on
– Damages
EC’s
of
capillaries
in
glomeruli
–
may
impair
ADAMTS13
on
these
EC’s)
3. Causes
release
of
ULvWF
à
platelet
ac7va7on
à
microthrombi
forma7on
à
renal
failure
4. TF
released
à
ac7va7on
of
coagula7on
cascade
à
fibrin
forma7on
5. Erythrocytes
damaged
as
trapped
in
thrombi
à
Schistocytes
+
intravascular
hemolysis
à
splenic
sequestra.on
6. Shiga
toxin
damages
the
endothelial
cell
causing
the
release
of
ULvWF
40

41. UPSHAW-­‐SHULMAN
SYNDROME
• Congenital
deficiency
of
ADAMTS-­‐13
1. Protease
cleaves
vWF
mul7mers
2. Presents
at
birth
with
hemoly7c
anemia
and
thrombocytopenia
3.
Renal
involvement
develops
later
in
life
•
Inhibitor
auto-­‐an7bodies
to
ADAMTS-­‐13
can
also
cause
similar
syndrome
Brass, L, 2001, Nature Med 7:1177-1178.

42. TTP
versus
HUS
TTP
HUS
• Adults—20-­‐50
• Children
<5
years
old
Pentad
Tetrad
• Hemoly7c
anemia
with
RBC
fragmenta7on
• Hemoly7c
anemia
with
RBC
fragmenta7on
• Renal
dysfunc7on
• Acute
renal
failure
• Thrombocytopenia
(35,000)
• Thrombocytopenia
(95,000)
• Severe
CNS
symptoms
• Mild
CNS
symptoms
• Fever
42

43. Disorders
of
the
Vascular
System
• Structural
abnormality
or
damage
either
to
the
endothelial
lining
or
the
subendothelial
structures
à
variety
of
clinical
manifesta7ons
• Disorders
classified
– Inherited
disorders
caused
by
• Abnormal
synthesis
of
subendothelial
connec7ve
7ssue
components
– Acquired
disorders
caused
by
an
underlying
disease
of
condi7on
• Decreases
the
suppor7ve
connec7ve
7ssue
in
the
blood
vessel
wall
• Abnormal
proteins
in
the
vascular
7ssue
• Infec7ons
or
allergic
condi7ons
• Mechanical
stress
43

44. Hereditary
Vascular
Disorders
• Hereditary
Hemorrhagic
Telangiectasia
(HTT)
– Gene7c
disorder
that
causes
abnormali7es
of
blood
vessels
– Blood
vessels
that
lack
capillaries
between
an
artery
and
vein
– Under
high
pressure
blood
flows
through
arteriovenous
malforma7ons
– These
are
fragile
sites
that
are
easily
ruptured
and
result
in
bleeding
– Can
occur
in
the
skin
or
any
organ
• Ehlers-­‐Danlos
Syndromes
(Oslo-­‐Weber-­‐Rendu
Syndrome)
– Heterogeneous
group
of
inherited
connecCve-­‐Cssue
disorders
characterized
1. Joint
hypermobility
2. Cutaneous
fragility
3. Hyperextensibility
– Associated
with
arterial
rupture
and
visceral
perforaCon,
with
possible
life-­‐threatening
consequences
44

45. Marfan
Syndrome
• Marfan
syndrome
is
an
autosomal
dominant
gene7c
disorder
of
the
connecCve
Cssue
• 1
in
5,000
people
in
the
United
States
have
the
disorder
• Unusually
long
limbs,
great
stature,
or
long
toes
(or
fingers)
in
propor7on
to
the
person's
height
• PredisposiCon
to
cardiovascular
disease
• Muta7on
in
the
fibrillin-­‐1
gene
(FBN1)—
chromosome
15
• Fibrillin—major
building
block
of
microfibrils
– Serves
as
substrate
for
elas7n
in
the
aorta
and
other
connecCve
Cssues
45

46. Acquired
Disorders
of
the
Vascular
System
• Acquired
disorders
caused
by
an
underlying
disease
of
condi7on
– Decreases
the
supporCve
connecCve
Cssue
in
the
blood
vessel
wall
• Senile
purpura
– Ecchymoses
that
appear
with
unrecognized
or
minor
trauma
in
elderly
individuals
– Extracellular
matrix
components
of
the
skin
degenerate
à
loss
of
suppor7ve
collagen
fibrils
à
capillaries
burst
with
minor
pressure
• Cushing
syndrome
and
corCcosteroid
therapy
– Excess
endogenous
glucocorCcosteroids
(Cushing
syndrome)
à
breakdown
in
collagen
– Exogenous
(therapeu7c)
glucocorCcosteroids
à
breakdown
in
collagen
• Scurvy
– Deficiency
of
vitamin
C
which
is
needed
for
collagen
synthesis
à
abnormal
collagen
producd7on
à
vascular
fragility
and
bleeding
46

47. Acquired
Disorders
of
the
Vascular
System
• Abnormal
proteins
in
the
vascular
Cssue
– Paraproteins
• Monoclonal
immunoglobulins
produced
by
monoclonal
neoplas7c
plasma
cells
• Paraproteins
bind
to
calcium
à
interference
with
coagula7on
and
deposi7on
of
light
chain
proteins
in
the
vascular
wall
– Amyloidoisis
• Deposits
of
amyloid
(misfolded
or
modified
protein)
form
in
the
skin,
perivascular
7ssue,
and
vessel
walls
à
leads
to
fragility
of
the
vessels
and
bruising
47

48. Acquired
Disorders
of
the
Vascular
System
• Henoch-­‐Schönlein
purpura
• Small-­‐vessel
vasculiCs
characterized
by
IgA,
C3,
and
immune
complex
deposi7on
in
arterioles,
capillaries,
and
venules
• HSP
affects
mostly
children
and
involves
the
skin
and
connec7ve
7ssues,
gastrointes7nal
tract,
joints,
and
scrotum
as
well
as
the
kidneys
• Drugs
– Drugs
from
almost
every
pharmacologic
class
have
been
implicated
in
causing
vasculi7s
in
sporadic
cases
48

49. Acquired
Disorders
of
the
Vascular
System
• Miscellaneous
causes
– Mechanical
purpura
• Increased
pressure
within
the
lumen
of
the
capillaries
azer
intense
exercise,
coughing
spasms
– Purpura
fulminans
• Associated
with
abnormali7es
of
certain
clong
factors
or
their
inhibitors
• Thrombi
form
in
small
vessels
supplying
the
skin
and
subcutaneous
7ssue
à
necrosis
49

50. Lab
Tests
in
Disorders
of
Primary
Hemostasis
Platelet
count
PT
APTT
Bleeding
Cme
Vascular
disorder
Normal
Normal
Normal
Normal
or
abnormal
Thrombocytopenia
Decreased
Normal
Normal
Abnormal
Platelet
Dysfunc7on
Usually
Normal
Normal
Normal
Normal
or
Abnormal
Most
vascular
diseases
1. Are
not
associated
with
platelet
or
plasma
defects
2. Most
common
symptom
• Abnormal
bleeding
into
or
under
the
skin
due
to
increased
permeability
to
blood
3. Laboratory
tests
are
used
to
exclude
• Coagula7on
or
platelet
disorders
4. Majority
of
pa7ents
• Hemosta7c
tes7ng
is
en7rely
normal,
despite
a
history
or
physical
examina7on
that
suggests
substan7al
bleeding
50