An obstetrician is urgently paged to the emergency room to evaluate a patient on her fourt… — USMLE Step 2 CK

An obstetrician is urgently paged to the emergency room to evaluate a patient on her fourth day postpartum. The patient, a $28$ -year-old primigravida who underwent an uncomplicated cesarean delivery, is now exhibiting profound agitation and visual hallucinations. Her husband, who accompanied her, states that these behavioral changes began abruptly $24$ hours ago alongside a new leg rash. A brief outpatient workup yesterday included blood cultures, which currently show no growth.

Initial assessment reveals the following vital signs:

Measurement	Value
Temperature	$38.6^\circ\text{C}$ ( $101.5^\circ\text{F}$ )
Blood pressure	$138/86\text{ mmHg}$
Heart rate	$112/\text{min}$
Respiratory rate	$18/\text{min}$
Oxygen saturation	$98\%$ on room air

During the physical examination, the patient is disoriented to time and space. Inspection of her skin reveals non-blanching, pinpoint purplish macules clustered on the bilateral lower extremities. The abdomen is non-tender, and the Pfannenstiel incision is dry and intact with no induration. Neurologic examination shows generalized hyperreflexia but no focal deficits.

Laboratory studies are obtained:

Test	Result	Reference Range
Hemoglobin	$7.2\text{ g/dL}$	$12.0-15.5\text{ g/dL}$
Platelets	$18,000/\text{mm}^3$	$150,000-400,000/\text{mm}^3$
Leukocytes	$9,200/\text{mm}^3$	$4,500-11,000/\text{mm}^3$
Creatinine	$2.1\text{ mg/dL}$	$0.6-1.1\text{ mg/dL}$
Total bilirubin	$3.4\text{ mg/dL}$	$0.1-1.2\text{ mg/dL}$
Indirect bilirubin	$3.0\text{ mg/dL}$	$0.1-0.8\text{ mg/dL}$
Prothrombin time (PT)	$12\text{ sec}$	$11-15\text{ sec}$
Partial thromboplastin time (PTT)	$30\text{ sec}$	$25-40\text{ sec}$
Thyroid-stimulating hormone (TSH)	$1.4\text{ mU/L}$	$0.4-4.0\text{ mU/L}$
Free T4	$0.6\text{ ng/dL}$	$0.9-1.7\text{ ng/dL}$

A peripheral blood smear demonstrates numerous fragmented erythrocytes with two or three pointed ends, and a marked paucity of platelets.

Which of the following is the most appropriate next step in management?

A
Perform a CT scan of the abdomen and pelvis
B
Administer intravenous vancomycin and cefepime
Initiate immediate plasma exchange therapyAnswer
D
Admit to the inpatient psychiatric unit and initiate haloperidol
E
Administer intravenous levothyroxine

Answer

Initiate immediate plasma exchange therapy

The correct management is to initiate immediate plasma exchange therapy. This patient's presentation of fever, altered mental status, thrombocytopenia, microangiopathic hemolytic anemia (MAHA), and acute kidney injury represents the classic pentad of Thrombotic Thrombocytopenic Purpura (TTP). TTP is a life-threatening hematologic emergency caused by autoantibodies against ADAMTS13, a metalloprotease responsible for cleaving large von Willebrand factor (vWF) multimers. Without this cleavage, ultra-large vWF multimers accumulate and trap passing platelets, causing widespread microvascular thrombosis, red blood cell shearing (schistocytes), and end-organ damage (brain, kidneys). Crucially, because TTP is primarily a platelet-consumptive disorder, the coagulation cascade is largely unaffected, resulting in normal PT and PTT values. This distinguishes TTP from Disseminated Intravascular Coagulation (DIC), which features prolonged coagulation times. Plasma exchange is the standard of care as it simultaneously removes the offending autoantibodies and replaces the deficient ADAMTS13 enzyme.

Step-by-Step Solution

Analyze the clinical presentation and laboratory findings

The patient exhibits fever, altered mental status, acute kidney injury (creatinine

2.1\text{ mg/dL}

), profound thrombocytopenia (

18,000/\text{mm}^3

), and microangiopathic hemolytic anemia (MAHA) evidenced by anemia, indirect hyperbilirubinemia, and schistocytes.

To identify the classic pentad of Thrombotic Thrombocytopenic Purpura (TTP).

Differentiate the diagnosis from similar coagulopathies

Prothrombin time (PT) and partial thromboplastin time (PTT) are within normal limits.

To rule out Disseminated Intravascular Coagulation (DIC), which would present with prolonged coagulation times due to the consumption of clotting factors.

Determine the definitive acute management for the identified condition

Plasma exchange therapy (plasmapheresis) is selected as the primary intervention.

To mechanically remove autoantibodies against the ADAMTS13 protease and replenish the deficient enzyme, thereby halting the formation of microthrombi.

Key Concept

Diagnosis and management of Thrombotic Thrombocytopenic Purpura (TTP)

Estimated Time:1m 30s

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Topics

More questions from this topic