A 42-year-old woman is brought to the emergency department by her husband due to progressi… — USMLE Step 2 CK

A $42$ -year-old woman is brought to the emergency department by her husband due to progressive confusion, lethargy, and a low-grade fever over the past $24$ hours. She has no significant past medical history. Her temperature is $37.8^\circ\text{C}$ ( $100.0^\circ\text{F}$ ), blood pressure is $142/88$ mmHg, and pulse is $105$ /min. Physical examination reveals petechiae on her lower extremities and scleral icterus. Neurologic examination shows a lethargic patient who is oriented only to person.

Laboratory studies show:

Test	Result
Hemoglobin	$8.2$ g/dL
Platelets	$22,000$ /mm $^3$
Leukocytes	$8,500$ /mm $^3$
Creatinine	$1.8$ mg/dL
Total bilirubin	$3.2$ mg/dL
Indirect bilirubin	$2.8$ mg/dL
Lactate dehydrogenase	$850$ U/L

Arrange the following steps in the most appropriate chronological order for the management of this patient.

1Perform a peripheral blood smear to identify schistocytes
2Obtain a baseline blood sample for ADAMTS13 activity
3Initiate emergent therapeutic plasma exchange (PEX)
4Monitor platelet count and lactate dehydrogenase (LDH) daily to assess treatment response

Answer

The correct sequence is: 1) Perform a peripheral blood smear to identify schistocytes, 2) Obtain a baseline blood sample for ADAMTS13 activity, 3) Initiate emergent therapeutic plasma exchange (PEX), and 4) Monitor platelet count and lactate dehydrogenase (LDH) daily to assess treatment response.

The patient's presentation of thrombocytopenia, hemolytic anemia, renal dysfunction, neurologic changes, and fever is highly suggestive of Thrombotic Thrombocytopenic Purpura (TTP). The first step is to confirm microangiopathic hemolytic anemia (MAHA) via a peripheral blood smear showing schistocytes. Once MAHA and thrombocytopenia are confirmed without another obvious cause, a presumptive diagnosis of TTP is made. Before administering any plasma, a blood sample for ADAMTS13 activity must be drawn, as donor plasma will alter baseline levels. Following this, therapeutic plasma exchange (PEX) must be initiated emergently. It is the primary life-saving treatment and should not be delayed while awaiting ADAMTS13 results. Finally, the patient's response to PEX and adjunctive immunosuppression is monitored daily by following the platelet count and LDH levels.

Step-by-Step Solution

Identify the clinical syndrome

Suspected Thrombotic Thrombocytopenic Purpura (TTP)

The patient presents with the classic pentad: fever, neurologic changes, thrombocytopenia, hemolytic anemia, and renal dysfunction.

Select the initial diagnostic test

Peripheral blood smear

Visualizing schistocytes confirms microangiopathic hemolytic anemia (MAHA), establishing the presumptive diagnosis of TTP.

Identify the necessary pre-treatment laboratory draw

ADAMTS13 activity and inhibitor assay

Blood must be drawn before giving donor plasma to accurately measure the patient's baseline enzyme activity.

Select the emergent definitive therapy

Therapeutic plasma exchange (PEX)

PEX removes autoantibodies and replenishes ADAMTS13; it must be started immediately without waiting for confirmatory assay results.

Determine the follow-up monitoring strategy

Daily monitoring of platelets and LDH

These markers indicate the resolution of microthrombi and hemolysis, guiding the duration of PEX.

Key Concept

Sequential management of suspected Thrombotic Thrombocytopenic Purpura (TTP)

Estimated Time:1m 30s

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