Hematology · Microangiopathic Hemolytic Anemia
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The pathophysiology of Thrombotic Thrombocytopenic Purpura (TTP) involves a severe deficiency of the ADAMTS13 metalloprotease, leading to the accumulation of ultra-large von Willebrand factor (vWF) multimers.
The classic pentad of TTP includes microangiopathic hemolytic anemia (MAHA), thrombocytopenia, fever, renal insufficiency, and fluctuating neurologic deficits.
Peripheral blood smear findings in TTP characteristically demonstrate schistocytes (helmet cells) resulting from mechanical shearing of red blood cells in platelet- and vWF-rich microthrombi.
Laboratory evaluation reveals elevated LDH, low haptoglobin, indirect hyperbilirubinemia, and a negative direct Coombs test confirming non-immune hemolysis.
The diagnosis of TTP is confirmed by demonstrating ADAMTS13 activity <10%; an ADAMTS13 inhibitor (autoantibody) is present in immune TTP but absent in congenital (Upshaw-Schulman) TTP.
The immediate first-line treatment for immune TTP is therapeutic plasma exchange (plasmapheresis) plus corticosteroids, with caplacizumab and rituximab added for acute episodes.
Platelet transfusions are strictly contraindicated in TTP unless there is life-threatening hemorrhage, as they may exacerbate microthrombi formation.
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A 34-year-old woman presents to the emergency department with a three-day history of confusion and fatigue. Physical examination reveals petechiae on the lower extremities and a temperature of 100.4°F. Laboratory studies show a hemoglobin of 8.2 g/dL, platelet count of 22,000/µL, and an elevated LDH. A peripheral blood smear shows numerous schistocytes, and the direct Coombs test is negative.
What is the most appropriate initial management for this patient?
Therapeutic plasma exchange
The patient presents with key features of TTP (MAHA, thrombocytopenia, fever, neurologic symptoms); note that the full pentad is present in a minority of patients and the dyad of MAHA plus thrombocytopenia is sufficient to act. Immediate plasma exchange is the gold-standard treatment to remove the ADAMTS13 inhibitor and restore protease activity.
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Etiology / Epidemiology
Autoimmune inhibition of ADAMTS13 protease leads to uncleaved von Willebrand factor multimers. Most common in adult women.
Clinical Manifestations
Classic pentad: thrombocytopenia, microangiopathic hemolytic anemia, fever, renal failure, and neurologic deficits.
Diagnosis
Diagnosis is clinical; ADAMTS13 activity <10% is the definitive confirmatory test.
Treatment
Plasmapheresis is the gold standard; never give platelets as they worsen microthrombi.
Prognosis
Untreated mortality is >90%; prompt initiation of therapy reduces mortality to <20%.
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Epidemiology & Etiology
TTP is a rare, life-threatening thrombotic microangiopathy. It is primarily caused by autoantibodies against the ADAMTS13 enzyme. Secondary causes include pregnancy, malignancy, or medications like clopidogrel.
Pertinent Anatomy
The pathology centers on the microvasculature of the brain, kidneys, and heart. Formation of platelet-rich thrombi in these small vessels leads to end-organ ischemia.
Pathophysiology
Deficiency of ADAMTS13 prevents the cleavage of ultra-large von Willebrand factor (vWF) multimers. These uncleaved multimers cause excessive platelet aggregation and systemic microthrombi. This process consumes platelets and shears RBCs, resulting in schistocytes on peripheral smear.
Clinical Manifestations
The classic pentad includes thrombocytopenia (petechiae/purpura), microangiopathic hemolytic anemia (jaundice/pallor), fever, renal insufficiency, and fluctuating neurologic symptoms. Do not wait for the full pentad to suspect TTP, as most patients present with only the dyad of microangiopathic hemolytic anemia and thrombocytopenia.
Diagnosis
The peripheral blood smear is the initial diagnostic step, showing hallmark schistocytes. The gold standard is ADAMTS13 activity assay, where levels <10% confirm the diagnosis. Labs show elevated LDH, indirect bilirubin, and low haptoglobin consistent with hemolysis.
Treatment
Immediate plasmapheresis (plasma exchange) is the first-line treatment to remove autoantibodies and replace ADAMTS13. Platelet transfusion is contraindicated as it fuels the fire of microthrombi formation. Corticosteroids are given concurrently with plasma exchange, and rituximab plus caplacizumab (anti-vWF nanobody) are recommended for acute immune TTP episodes.
Prognosis
Without treatment, TTP is nearly universally fatal. Relapse occurs in 30-40% of patients, requiring long-term monitoring of platelet counts and ADAMTS13 levels.
Differential Diagnosis
HUS: renal failure is the dominant feature, usually post-diarrheal
DIC: abnormal coagulation studies (PT/PTT) distinguish it from TTP
ITP: isolated thrombocytopenia without hemolytic anemia
Evans Syndrome: autoimmune hemolytic anemia plus immune thrombocytopenia
HELLP Syndrome: occurs specifically in the setting of pregnancy/preeclampsia