A 32-year-old female patient is assessed on hospital day 4. She was initially admitted for… — USMLE Step 2 CK

A $32$ -year-old female patient is assessed on hospital day $4$ . She was initially admitted for high fevers, rigors, and pleuritic chest pain. Her past medical history is significant for major depressive disorder managed with citalopram, and severe opioid use disorder. On the day of admission, physical examination revealed a pan-systolic murmur at the left lower sternal border that augmented during inspiration. Blood cultures from admission grew methicillin-susceptible *Staphylococcus aureus* (MSSA). A transthoracic echocardiogram showed a $1.6$ -cm oscillating mass on the tricuspid valve. She was appropriately started on targeted therapy with continuous intravenous nafcillin.

Currently, she reports mild improvement in her chest pain but notes a persistent cough. Her temperature is $37.9^\circ \text{C}$ ( $100.2^\circ \text{F}$ ), blood pressure is $114/70$ mmHg, pulse is $92$ /min, and respiratory rate is $18$ /min. Pulse oximetry shows $95\%$ on room air. Auscultation of the lungs reveals coarse crackles in the periphery of both lung fields. The cardiac examination is unchanged from admission. There is no jugular venous distention and no peripheral edema.

Laboratory tests reveal:
Leukocyte count: $12,200$ /mm $^3$
Thyroid-stimulating hormone (TSH): $1.4\ \mu\text{U/mL}$ (Normal: $0.5 - 5.0\ \mu\text{U/mL}$ )
Free thyroxine (T4): $1.1\ \text{ng/dL}$ (Normal: $0.9 - 1.7\ \text{ng/dL}$ )
Total triiodothyronine (T3): $62\ \text{ng/dL}$ (Normal: $80 - 200\ \text{ng/dL}$ )

A repeat chest radiograph demonstrates several new, small cavitary lesions scattered throughout the peripheral lung fields bilaterally.

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

A
Administer intravenous furosemide
B
Switch nafcillin to intravenous vancomycin
C
Discontinue nafcillin and initiate intravenous linezolid
Continue intravenous nafcillin and observeAnswer
E
Initiate oral levothyroxine therapy

Answer

The correct answer is to continue intravenous nafcillin and observe. The patient is demonstrating appropriate clinical improvement, and the new cavitary lung lesions represent septic pulmonary emboli, an expected complication of right-sided infective endocarditis that will gradually resolve with continued targeted antibiotic therapy.

The most appropriate next step is to continue intravenous nafcillin and observe. This patient has right-sided (tricuspid valve) infective endocarditis due to MSSA, often seen in patients with a history of intravenous drug use. Septic pulmonary emboli—which present with cough, pleuritic chest pain, hemoptysis, and peripheral cavitary lesions on imaging—occur in up to

75\%

of patients with tricuspid valve endocarditis. As fragments of the vegetation embolize to the pulmonary vasculature, they cause localized infarction and abscess formation. Despite this complication, the patient's overall clinical status is improving (decreasing temperature and down-trending leukocyte count). Fevers may persist for up to a week after initiating appropriate antibiotics for endocarditis. Therefore, surgical intervention or a change in antibiotics is not indicated at this time; the septic emboli will slowly resolve with the continuation of effective targeted antimicrobial therapy.

Step-by-Step Solution

Analyze the primary diagnosis and current treatment status.

The patient has native-valve right-sided infective endocarditis caused by MSSA, appropriately treated with intravenous nafcillin.

To establish the baseline clinical scenario and confirm that the initial antimicrobial stewardship was correct.

Evaluate the new pulmonary symptoms and radiographic findings.

The persistent cough, peripheral crackles, and new cavitary lesions represent septic pulmonary emboli, which are a hallmark complication of tricuspid valve endocarditis.

To determine whether the new lung findings are an expected complication of the primary disease or a sign of treatment failure/new pathology.

Assess the overall clinical trajectory.

Despite the new lung lesions, the patient is hemodynamically stable, her fever is decreasing, and her leukocytosis is improving, indicating that the current antibiotic regimen is effective.

To decide whether a change in medical or surgical management is warranted.

Interpret the laboratory data regarding thyroid function.

The patient has a low T3 level but normal TSH and Free T4, which is diagnostic of euthyroid sick syndrome (non-thyroidal illness syndrome).

To avoid inappropriate pharmacological intervention for a normal physiologic response to systemic illness.

Formulate the final management plan.

Continue the current targeted antibiotic (nafcillin) without adding contraindicated medications or unnecessary treatments.

To ensure optimal patient outcomes and adhere to proper antibiotic stewardship and polypharmacy guidelines.

Key Concept

Management of right-sided infective endocarditis and its expected complications, such as septic pulmonary emboli.

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