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

A 34-year-old woman is brought to the emergency department by her husband due to progressive confusion and severe fatigue over the past 48 hours. Her temperature is $37.8^\circ\text{C}$ , blood pressure is $142/88 \text{ mmHg}$ , and pulse is $108/\text{min}$ . Physical examination reveals scleral icterus and scattered petechiae on the lower extremities. Neurological examination shows mild disorientation but no focal motor deficits.

Laboratory studies show:

Laboratory Test	Result	Reference Range
Hemoglobin	$7.4 \text{ g/dL}$	$12.0-16.0 \text{ g/dL}$
Platelet count	$18,000/\text{mm}^3$	$150,000-400,000/\text{mm}^3$
Mean corpuscular volume	$86 \text{ fL}$	$80-100 \text{ fL}$
Creatinine	$1.6 \text{ mg/dL}$	$0.6-1.2 \text{ mg/dL}$
Total bilirubin	$3.8 \text{ mg/dL}$	$0.1-1.2 \text{ mg/dL}$
Direct bilirubin	$0.6 \text{ mg/dL}$	$0.0-0.3 \text{ mg/dL}$
Lactate dehydrogenase (LDH)	$1,450 \text{ U/L}$	$100-250 \text{ U/L}$
INR	$1.1$	$0.8-1.2$
aPTT	$32 \text{ seconds}$	$25-40 \text{ seconds}$

Arrange the following clinical steps in the most appropriate sequential order for the evidence-based diagnosis and management of this patient.

1Review a peripheral blood smear for the presence of schistocytes.
2Calculate the PLASMIC score to assess the pretest probability of severe ADAMTS13 deficiency.
3Obtain a venous blood sample for ADAMTS13 activity and inhibitor testing.
4Initiate emergent therapeutic plasma exchange (PLEX).
5Administer high-dose systemic glucocorticoids.

Answer

The correct sequence is: Review a peripheral blood smear -> Calculate the PLASMIC score -> Obtain a venous blood sample for ADAMTS13 -> Initiate emergent therapeutic plasma exchange (PLEX) -> Administer high-dose systemic glucocorticoids.

The patient's presentation of MAHA, severe thrombocytopenia, mild renal impairment, and neurological symptoms without coagulopathy strongly suggests Thrombotic Thrombocytopenic Purpura (TTP). The evidence-based sequence begins with identifying MAHA on a peripheral smear. Next, a PLASMIC score is calculated to risk-stratify the patient; this patient has a high score due to hemolysis, platelets < 30,000, MCV < 90, normal INR, and Cr < 2.0. Critically, the blood sample for ADAMTS13 must be drawn *before* any plasma therapy is administered to prevent false-negative diagnostic results. Once the sample is secured, emergent therapeutic plasma exchange (PLEX) is initiated empirically without waiting for the ADAMTS13 results. Finally, adjunctive medical therapies like glucocorticoids are added to target the underlying autoimmune antibody production.

Step-by-Step Solution

Evaluate the CBC and standard laboratory panels by reviewing a peripheral blood smear.

Confirmation of fragmented red blood cells (schistocytes), establishing the presence of microangiopathic hemolytic anemia (MAHA).

Before initiating invasive treatment for Thrombotic Thrombocytopenic Purpura (TTP), MAHA must be distinguished from other causes of pancytopenia or isolated thrombocytopenia.

Calculate the PLASMIC score using the patient's laboratory values and clinical history.

A high score (e.g., 6 or 7) strongly suggests severe ADAMTS13 deficiency.

This validated predictive tool helps clinicians justify the immediate use of high-risk, expensive empiric therapies (like PLEX) before definitive molecular testing results are available.

Draw a venous blood sample for an ADAMTS13 activity and inhibitor assay.

The diagnostic specimen is safely secured prior to any treatment.

PLEX utilizes donor fresh frozen plasma, which contains functional ADAMTS13 enzyme. Drawing blood after starting PLEX yields falsely normalized results, permanently obscuring the true diagnosis.

Initiate emergent therapeutic plasma exchange (PLEX).

Mechanical removal of ADAMTS13 autoantibodies and replenishment of the functional enzyme.

TTP is a medical emergency with high mortality if untreated. PLEX must be started immediately upon clinical suspicion and must not wait for the ADAMTS13 laboratory results.

Administer systemic immunosuppressants, such as high-dose glucocorticoids.

Suppression of the underlying autoimmune pathophysiology.

While PLEX manages the acute thrombotic crisis, immunosuppressants halt the ongoing production of the pathogenic IgG autoantibodies.

Key Concept

Diagnosis and stepwise management algorithm for Thrombotic Thrombocytopenic Purpura (TTP)

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