Examkin

Question

Difficulty: MediumFormulating a Differential Diagnosis

A 34-year-old woman is brought to the emergency department by her husband due to progressive confusion and lethargy over the past 48 hours. She has also had a low-grade fever and feels profoundly fatigued. She has no significant past medical history and takes no medications. Her temperature is 38.2∘C38.2^\circ\text{C} (100.8∘F100.8^\circ\text{F}), blood pressure is 118/74 mmHg118/74\text{ mmHg}, and pulse is 105/min105/\text{min}. Physical examination reveals scleral icterus and scattered petechiae over her lower extremities. Neurological examination is notable for disorientation to time and place, but no focal motor or sensory deficits are present. Laboratory studies are obtained:

Laboratory StudyResult
Hemoglobin7.8 g/dL7.8\text{ g/dL}
Platelet count18,000/mm318,000/\text{mm}^3
Leukocyte count8,500/mm38,500/\text{mm}^3
Creatinine2.2 mg/dL2.2\text{ mg/dL}
Total bilirubin3.8 mg/dL3.8\text{ mg/dL}
Indirect bilirubin3.1 mg/dL3.1\text{ mg/dL}
Lactate dehydrogenase1,450 U/L1,450\text{ U/L}
Prothrombin time12 seconds12\text{ seconds}
Activated partial thromboplastin time30 seconds30\text{ seconds}

A peripheral blood smear reveals numerous schistocytes.

Which of the following is the most likely diagnosis?

  1. Thrombotic thrombocytopenic purpuraAnswer
  2. B
    Disseminated intravascular coagulation
  3. C
    Immune thrombocytopenia
  4. D
    Hemolytic uremic syndrome
  5. E
    Systemic lupus erythematosus

Answer

The correct diagnosis is thrombotic thrombocytopenic purpura.
The correct diagnosis is thrombotic thrombocytopenic purpura (TTP). This patient presents with the classic pentad of TTP: microangiopathic hemolytic anemia (evidenced by anemia, elevated LDH, elevated indirect bilirubin, and schistocytes), thrombocytopenia, acute kidney injury, fever, and neurologic abnormalities (confusion and disorientation). The underlying pathophysiology involves a deficiency of the ADAMTS13 metalloproteinase, leading to uncleaved, ultra-large von Willebrand factor multimers that trap platelets and shear red blood cells. Crucially, the normal prothrombin time (PT) and activated partial thromboplastin time (aPTT) distinguish TTP from consumptive coagulopathies.

Step-by-Step Solution

1
Analyze the patient's clinical presentation and preliminary laboratory findings.
The patient has microangiopathic hemolytic anemia (anemia, elevated indirect bilirubin, elevated LDH, schistocytes), thrombocytopenia, acute kidney injury (elevated creatinine), fever, and neurologic changes.
Identifying the clinical syndrome is the first step in formulating a targeted differential diagnosis.
2
Evaluate the coagulation profile.
Both the prothrombin time (PT) and activated partial thromboplastin time (aPTT) are within normal limits.
Normal coagulation studies are crucial for distinguishing primary thrombotic microangiopathies (like TTP and HUS) from systemic consumptive coagulopathies (like DIC).
3
Differentiate between the remaining thrombotic microangiopathies based on clinical presentation.
The presence of the classic pentad—particularly the prominent neurological symptoms and fever in an adult without a preceding diarrheal illness—strongly favors TTP over HUS.
TTP and HUS exist on a spectrum, but distinguishing them relies on the predominant organ system involvement and the patient's clinical history.

Key Concept

Patients presenting with microangiopathic hemolytic anemia and thrombocytopenia require immediate evaluation of their coagulation profile to rule out DIC, followed by clinical differentiation to identify TTP, characterized by its classic pentad (fever, anemia, thrombocytopenia, renal failure, neurologic symptoms).
Rate this question

Topics

Formulating a Differential Diagnosis

More questions from this topic