Dr. Brijendra Bahadur Singh KGMU, LUCKNOW

Microangiopathic Hemolytic Anemia

PATHOGENESIS• Mechanical shearing of RBC membranes as the cell rapidly pass

through turbulent areas of small blood vessels partially blocked by micro thrombi or damaged endothelium.

• Upon shearing , RBC membranes quickly reseal with minimal escape of hemoglobin and schistocytes are formed.

• Thromobocytopenia occurs due to consumption of platelets in the thrombi formed in microvasculature

• Schistocytes in the PBS- Characteristic feature• Grading of schistocytes- Fragmented red cells as % off all red cells - <1% - occasional 1%- 3% - 1+ 3% - 6%- 2+ 6%- 12%- 3+ >12% - 4+

• Helmet cells, Microspherocytes, polychromasia & nRBC• Thrombocytopenia

Causes of MAHA• Thrombotic thrombocytopenic purpura(TTP)• Hemolytic uremic syndrome(HUS)• HELLP syndrome• Disseminated intravascular coagulation • Severe burns• Malignant hypertension• SLE, Scleroderma• Drugs- Cyclosporin, Gemcitabane, Mitomycin –c• C. difficile, R. rickettsii, B. anthracis

THROMBOTIC THROMBOCYTOPENIC PURPURA• Moschowitz syndrome

• Most common in adults, 4th decade, F>M

• Characterized by i. MAHAii. severe thrombocytopenia iii. serum LDH activity

• Neurological dysfunction, fever and renal failure

• Deficiency of vWF cleaving protease known as a disintegrin and metalloproteinase with a thrombospondin type 1 motiff, member 13(ADAMTS- 13)

Pathogenesis of TTP ( contd.)• ADAMTS13 serves an important antithrombotic

function by preventing VWF excessive binding and activating platelets

• Platelets- VWF microthrombi block small blood vessels results in thrombocytopenia, ischemia in brain, kidney and other organs; and hemolytic anemia due to RBC rupture

• Intravascular hemolysis and extensive tissue ischemia result in a striking increase in serum LDH

TYPES OF TTP• Idiopathic

• Secondary

• Inherited

Idiopathic TTP

• No precipitating event• Autoantibodies to ADAMTS13 • Autoantibodies are usually IgG class but can be IgM or

IgA

Secondary TTP

• Infections, pregnancy, surgery, trauma, inflammation and disseminated malignancy possibly by depressing the synthesis of ADAMTS13

• Inhibitory reaction to ADAMTS13 occurs in conditions like hematopoietic stem cell transplantation; autoimmune disorders; HIV; drugs like quinine, ticlopidine and trimethoprim

Inherited TTP• Upshaw-schulman syndrome

• Severe ADAMTS13 deficiency by mutation in the ADAMTS13 gene

• May present in infancy or childhood with recurrent episodes

Laboratory findings of TTP and HUS• Hematologic- o↓hemoglobino↓plateletso↑ reticulocyte count

• PBS-oSchistocytesoPolychromasiaonRBC(severe cases)

• Biochemicalo↑LDH activityo↑ serum total and indirect bilirubino↓serum haptoglobin level

• Hemoglobinemia• Hemoglobinuria• Proteinuria• Hematuria

Treatment of TTP

• Idiopathic TTP- 80 to 90% patients respond to plasma exchange therapy• Corticosteroids are useful to suppress autoimmune

response• Rituximab- in relapsing TTP• Secondary TTP- do not respond well to plasma

exchange, prognosis is poor except for TTP is related to autoimmune disease, pregnancy and ticlodipine use• Inherited TPP- infusion of fresh frozen plasma

HEMOLYTIC UREMIC SYNDROME

• Characterized by MAHA, thrombocytopenia and acute renal failure• Two types- 1-Typical HUS 2- Atypical HUS• Typical HUS- K/A Shiga toxin –associated HUS or Stx- HUS• Comprises 90% cases of HUS

• Most common cause is infection with Shiga toxin producing Escherichia coli(STEC) such as serotype O157:H7, some strains of Shigella have also implicated

Pathogenesis of typical HUS• Absorbed from the intestine into plasma• Gb3 glycolipid receptors( CD77) on endothelial cells particularly in

glomerulus and brain

• Inhibit protein synthesis, causes endothelial cell injury and apoptosis

• Shiga toxin along with other cytokines secreted causes prothrombotic changes – expression of TF, secretion of ULVWF multimers

• Platelet activation and formation of platelet- fibrin thrombi results in blockage of microvasculature of glomeruli- Acute renal failure

Atypical HUS• 10% of cases

• Uncontrolled activation of alternative complement system

• 50% to 70% of patients have inherited mutations in gene

• Inactivating mutations in genes for complement regulatory proteins including complement factor H, complement factor I, membrane cofactor protein and thrombomodulin

• Activating mutations in genes for complement factor B and C3

• An acquired form of aHUS is associated with autoantibodies against complement factor H in 5 %to 10% of cases

HELLP SYNDROME• Hemolysis, elevated liver enzymes and low platelet count• < 1% of all pregnancies but develops in approximately 10 % to

20% of pregnancies with severe preeclampsia( mc 3rd trimester)• Exact pathogenesis is not known• In pre-eclampsia, abnormalities in the development of placental

vasculature result in poor perfusion and hypoxia • Antiangiogenic proteins are released from the placenta that blocks

the action of placental growth factors• Continued vascular insufficiency leads to endothelial cell

dysfunction causing platelet activation and fibrin deposition in the microvasculature, particularly in liver

• Anemia, biochemical evidence of hemolysis and schistocytes in pbs • Platelet count is < 100x109 /L• ↑Serum LDH activity • ↑Serum aspartate aminotransferase activity

• ↓ platelet count, ↑LDH, ↑aspartate aminotransferase activity are major diagnostic criteria for the HELLP syndrome

• Therapy includes delivery of fetus and placenta as soon as possible, control seizures, hypertension and fluid balance• Mortality rate for mother – 3% to 5% and for fetus- 9% to 24%

DISSEMINATED INTRAVASCULAR COAGULATION• Defibrination syndrome or consumption coagulopathy• Generalized activation of hemostasis secondary to

systemic disease• Fibrin microthrombi partially occlude vessels and

consume platelets, coagulation factors, coagulation control proteins and fibrinolytic enzymes

• Fibrin degradation products including D- dimer, become elevated

• Acute and uncompensated DIC- deficiencies of multiple hemostasis components

• Chronic DIC- normal or even elevated clotting factors levels

• In chronic DIC, liver coagulation factor production and bone marrow platelet production compensate for increased consumption

• Although DIC is a thrombotic process, thrombi are small and ineffective, so systemic hemorrhage is first or most apparent sign

• Acute DIC is often fatal and requires immediate medical intervention

CAUSES

Pathogenesis of DIC (contd.)• Circulating thrombin is major culprit , activates platelets, activates

coagulation proteins and catalyzes fibrin formation

• Fibrinolytic system may become activated at the level of plasminogen

• Endothelial cell damaged releasing coagulation active substances

• Leukocytes particularly monocytes may be induced to release tissue factor

• Fibrin monomers fails to polymerize and coats platelets and coagulation proteins creating anticoagulant effect

• Plasmin circulates in plasma and digests all forms of fibrinogen and fibrin• Fibrin degradation products labeled X, Y, D , E and D dimer

are detectable in plasma exceeding 20,000ng/mL• Symptoms of organ failure such as renal function

impairment, ARDS, CNS manifestations• Skin , bone and bone marrow necrosis may be seen• Purpura fulminans is seen in meningococcemia, chicken

pox and spirochete infections

DIC PROFILETEST REFRENCE INTERVAL VALUE IN DIC

Platelet count 1.5-4.5 lac/ <1.5 lac/

Prothrombin time 11-14sec >14 sec

PTT 25-35 sec >35 sec

D-Dimer 0-240 ng/mL > 240ng/mL, often 10,000 to 20,000 ng/mL

Fibrinogen 220-498mg/dL <220 mg/dL

Treatment of DIC

• Surgery, anti-inflammatory agents, antibiotics, obstetric procedures may normalize hemostasis , particularly in chronic DIC

• In acute DIC , treatment falls in 2 categories A) Therapy that slow the clotting processB) Therapy that replace missing platelets and coagulation factors

• UFH may be used for its antithrombotic properties but it may aggravate bleeding so careful observation and support needed

• Thawed frozen plasma provides all the coagulation factor and replaces blood volume lost

• Prothrombin complex concentrate, fibrinogen concentrate and factor VIII concentrate may be used in place of plasma

• Repeated measurements of fibrinogen, PT, PTT

• Platelet transfusion if severe thrombocytopenia

• Red blood cells are administered to treat anemia

• Antifibrinolytic therapy is contraindicated, except in proven systemic fibrinolysis

A 25 year old pregnant lady presents with thrombocytopenia(platelet count< 50,000) and fragmented RBC’S in peripheral smear. Which of the following is the least likely differential diagnosis?A- Thrombotic thrombocytopenic purpuraB- Disseminated intravascular coagulationC- HELLP syndromeD- Evans’s syndrome

What RBC morphology is characteristically found in Microangiopathic hemolytic anemiaA- Macrocytosis and polychromasiaB- Schistocytes and microspehrocytesC- Howell- jolly bodies and bite cellsD- Burr cells and crenated cells

A 36 years old woman was brought to the emergency department by her husband because she had experienced a seizure. He reported that she had been well until that morning, when she complained of sudden headache and ,malaise. She was not taking any medications and had no history of previous surgery or pregnancy. Laboratory studies showed a WBC count of 15x109 /L, Hb- 7.8g/dL, platelet count of 18x109 /L and schistocytes and helmet cells in peripheral blood film. Chemistry test results included markedly raised serum LDH activity and slight increase in total and indirect bilirubin. The urinalysis results were positive for protein and blood, but there were no RBCs in urine sediment. PT and PTT were with in reference interval. Which of the following in the most likely diagnosisA- HUSB-HELLP C-TTPD-DIC

ADAMTS13 deficiency is associated with:A- HELLP syndromeB- DICC- TTPD- HUS

Which of the following tests yields results that are abnormal in DIC but are usually within reference interval or just slightly abnormal in TTP and HUSA- Indirect serum bilirubin and serum haptoglobinB- Prothrombin time and partial thromboplastin timeC- LDH and ASTD- Serum creatinine and serum total protein

Weibel – palade bodies are storage granules for A- ThrombinB- CollagenC- VWFD- Epinephrine