A 34-year-old woman is brought to the emergency department by her partner due to confusion… — USMLE Step 2 CK

A $34$ -year-old woman is brought to the emergency department by her partner due to confusion and difficulty speaking that began this morning. Over the past three days, she has experienced fatigue, generalized weakness, and subjective fever. She has no significant past medical history and takes no medications. Her temperature is $38.4^\circ\text{C}$ ( $101.1^\circ\text{F}$ ), blood pressure is $145/88\text{ mmHg}$ , pulse is $112/\text{min}$ , and respiratory rate is $18/\text{min}$ . Physical examination reveals scleral icterus and scattered petechiae over the lower extremities. Neurological examination is notable for fluctuating lethargy and expressive aphasia.

Laboratory studies show the following:

Laboratory Test	Result	Reference Range
Hemoglobin	$7.8\text{ g/dL}$	$12.0$ - $15.5\text{ g/dL}$
Mean corpuscular volume	$92\text{ fL}$	$80$ - $100\text{ fL}$
Platelets	$18,000/\text{mm}^3$	$150,000$ - $400,000/\text{mm}^3$
Leukocytes	$8,400/\text{mm}^3$	$4,500$ - $11,000/\text{mm}^3$
Blood urea nitrogen	$38\text{ mg/dL}$	$7$ - $18\text{ mg/dL}$
Serum creatinine	$2.4\text{ mg/dL}$	$0.6$ - $1.2\text{ mg/dL}$
Total bilirubin	$4.1\text{ mg/dL}$	$0.1$ - $1.2\text{ mg/dL}$
Indirect bilirubin	$3.2\text{ mg/dL}$	$0.1$ - $0.8\text{ mg/dL}$
Lactate dehydrogenase	$1,450\text{ U/L}$	$100$ - $250\text{ U/L}$
Prothrombin time	$13\text{ seconds}$	$11$ - $15\text{ seconds}$
Activated partial thromboplastin time	$32\text{ seconds}$	$25$ - $40\text{ seconds}$

A peripheral blood smear demonstrates numerous fragmented red blood cells. Which of the following is the most critical initial intervention for this patient?

Centrifugal separation of the patient's plasma and replacement with donor plasmaAnswer
B
Transfusion of pooled donor apheresis platelets
C
Intravenous administration of broad-spectrum antimicrobial therapy
D
Intravenous infusion of pooled human immune globulin
E
Initiation of continuous venovenous hemofiltration

Answer

Centrifugal separation of the patient's plasma and replacement with donor plasma

The correct answer describes plasma exchange (plasmapheresis), which is the primary, life-saving treatment for Thrombotic Thrombocytopenic Purpura (TTP). TTP is a thrombotic microangiopathy typically caused by severely reduced activity of the von Willebrand factor (vWF)-cleaving protease ADAMTS13, most commonly due to an acquired autoantibody. This deficiency leads to the accumulation of ultra-large vWF multimers that consume platelets and form microthrombi in small blood vessels, causing diffuse end-organ ischemia. The classic pentad of TTP includes microangiopathic hemolytic anemia (MAHA), thrombocytopenia, acute kidney injury, neurologic changes, and fever. Immediate plasma exchange is therapeutic because it simultaneously removes the offending circulating ADAMTS13 autoantibodies and replenishes functional ADAMTS13 enzyme from the donor plasma.

Step-by-Step Solution

Analyze the clinical presentation and physical examination findings.

The patient presents with an acute onset of fever, altered mental status, expressive aphasia, and petechiae, indicating a systemic disease process involving the central nervous system and platelets.

Identifying the affected organ systems helps narrow the differential diagnosis for acute systemic illness.

Evaluate the laboratory values and peripheral blood smear.

Labs reveal severe thrombocytopenia, acute kidney injury, and non-immune hemolytic anemia (elevated LDH, indirect hyperbilirubinemia, and schistocytes). Coagulation studies (PT and aPTT) are strictly within normal limits.

Normal coagulation studies distinguish this microangiopathic process from Disseminated Intravascular Coagulation (DIC).

Synthesize the findings to formulate a definitive diagnosis.

The classic pentad of fever, neurological abnormalities, thrombocytopenia, microangiopathic hemolytic anemia, and renal insufficiency confirms the diagnosis of Thrombotic Thrombocytopenic Purpura (TTP).

Recognizing this pentad (or the essential dyad of MAHA and thrombocytopenia) is necessary to diagnose TTP, a true hematologic emergency.

Determine the most appropriate initial life-saving intervention.

Plasma exchange is the primary treatment, acting to remove the circulating ADAMTS13 autoantibodies and replenish the deficient functional enzyme.

Without immediate plasma exchange, mortality from TTP approaches 90% due to progressive organ ischemia.

Key Concept

Diagnosis and emergent management of Thrombotic Thrombocytopenic Purpura (TTP)

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