A 34-year-old woman is brought to the emergency department by her husband due to a 3-day h… — USMLE Step 3

A 34-year-old woman is brought to the emergency department by her husband due to a 3-day history of progressive confusion, severe headache, and profound fatigue. She has also had a subjective fever. The patient has no significant past medical history and takes no medications. Her temperature is $38.2^\circ\text{C}$ ( $100.8^\circ\text{F}$ ), blood pressure is $145/88\text{ mmHg}$ , heart rate is $105/\text{min}$ , and respiratory rate is $18/\text{min}$ . On physical examination, she appears lethargic but is oriented to person and place. Scleral icterus and mucosal pallor are present. There are scattered petechiae over her lower extremities. Neurological examination reveals no focal deficits, but her attention span is significantly impaired.

Laboratory evaluation shows the following:

Test	Result	Reference Range
Hemoglobin	$7.8\text{ g/dL}$	$12.0-15.5\text{ g/dL}$
Platelet count	$18,000/\text{mm}^3$	$150,000-400,000/\text{mm}^3$
Leukocyte count	$8,200/\text{mm}^3$	$4,500-11,000/\text{mm}^3$
Prothrombin time (PT)	$12\text{ sec}$	$11-15\text{ sec}$
Activated PTT	$28\text{ sec}$	$25-40\text{ sec}$
Fibrinogen	$320\text{ mg/dL}$	$150-400\text{ mg/dL}$
Creatinine	$1.9\text{ mg/dL}$	$0.6-1.1\text{ mg/dL}$
Total bilirubin	$3.2\text{ mg/dL}$	$0.1-1.2\text{ mg/dL}$
Indirect bilirubin	$2.8\text{ mg/dL}$	$0.1-0.8\text{ mg/dL}$
Lactate dehydrogenase (LDH)	$1,150\text{ U/L}$	$100-250\text{ U/L}$
Haptoglobin	$< 10\text{ mg/dL}$	$41-165\text{ mg/dL}$

Peripheral blood smear reveals numerous fragmented red blood cells (schistocytes) and absent platelets.

Based on the laboratory and clinical findings, which of the following is the most likely diagnosis?

Thrombotic thrombocytopenic purpuraAnswer
B
Disseminated intravascular coagulation
C
Immune thrombocytopenic purpura
D
Evans syndrome
E
Severe vitamin B12 deficiency

Answer

Thrombotic thrombocytopenic purpura

The correct answer is thrombotic thrombocytopenic purpura (TTP). This patient's laboratory results demonstrate microangiopathic hemolytic anemia (MAHA) and severe thrombocytopenia. The presence of schistocytes, elevated indirect bilirubin, high LDH, and low haptoglobin confirms intravascular hemolysis. Crucially, the normal PT, aPTT, and fibrinogen levels distinguish TTP from disseminated intravascular coagulation (DIC). The classic clinical pentad of TTP includes MAHA, thrombocytopenia, neurological abnormalities, fever, and renal insufficiency, all of which are present or evolving in this patient.

Step-by-Step Solution

Analyze the complete blood count and hemolysis markers.

The patient has severe thrombocytopenia and microangiopathic hemolytic anemia (MAHA), evidenced by low hemoglobin, schistocytes, elevated LDH, elevated indirect bilirubin, and low haptoglobin.

Identifying the type of anemia and the presence of concurrent cytopenias narrows the initial differential diagnosis.

Evaluate the coagulation panel.

Prothrombin time (PT), activated partial thromboplastin time (aPTT), and fibrinogen are all within normal limits.

In patients presenting with MAHA and thrombocytopenia, evaluating coagulation studies is critical to exclude disseminated intravascular coagulation (DIC).

Synthesize laboratory findings with the clinical presentation.

The combination of MAHA, severe thrombocytopenia, normal coagulation studies, fever, and acute neurologic changes (confusion) classically defines thrombotic thrombocytopenic purpura (TTP).

TTP is a medical emergency that requires prompt clinical recognition based on this specific constellation of laboratory and clinical findings.

Key Concept

Differentiating microangiopathic hemolytic anemias based on coagulation studies (TTP vs. DIC)

Estimated Time:1m 30s

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