A 28-year-old woman is brought to the emergency department by her husband due to a 1-week … — USMLE Step 2 CK

A 28-year-old woman is brought to the emergency department by her husband due to a 1-week history of worsening fatigue, facial rash, and shortness of breath that is exacerbated by deep inspiration. She was diagnosed with systemic lupus erythematosus (SLE) 4 years ago but stopped taking her prescribed mycophenolate mofetil and hydroxychloroquine 8 months ago. Her temperature is 38.6°C (101.5°F), blood pressure is 155/95 mmHg, heart rate is 110/min, and respiratory rate is 24/min. Physical examination reveals an erythematous rash across her cheeks and nasal bridge that spares the nasolabial folds. Lung auscultation demonstrates decreased breath sounds at the bilateral bases and a pleural friction rub. Mild jugular venous distention is present.

Laboratory studies show:

Laboratory Test	Result	Reference Range
Hemoglobin	9.2 g/dL	12.0–16.0 g/dL
Leukocyte count	2,800/mm³	4,500–11,000/mm³
Platelet count	95,000/mm³	150,000–400,000/mm³
Blood urea nitrogen	42 mg/dL	7–18 mg/dL
Serum creatinine	2.4 mg/dL	0.6–1.2 mg/dL
Thyroid-stimulating hormone (TSH)	1.1 mU/L	0.5–5.0 mU/L
Free T4	0.7 ng/dL	0.9–1.7 ng/dL

Arterial blood gas analysis on room air reveals:

Arterial Blood Gas	Result	Reference Range
pH	7.28	7.35–7.45
$pCO_2$	26 mmHg	35–45 mmHg
$pO_2$	88 mmHg	75–105 mmHg
$HCO_3^-$	12 mEq/L	22–28 mEq/L

Urinalysis shows 3+ protein, 20-30 red blood cells/hpf, and red blood cell casts. A urine culture obtained on admission grows >100,000 CFU/mL of *Escherichia coli* that is sensitive to amoxicillin, ceftriaxone, and nitrofurantoin. Blood cultures are pending.

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

Initiate high-dose intravenous methylprednisoloneAnswer
B
Administer intravenous sodium bicarbonate for inadequately compensated metabolic acidosis
C
Initiate intravenous meropenem to treat the urinary tract infection and systemic symptoms
D
Administer intravenous furosemide and noninvasive ventilation for acute decompensated heart failure
E
Begin oral levothyroxine supplementation for suspected secondary hypothyroidism

Answer

Initiate high-dose intravenous methylprednisolone

The patient is experiencing a severe, organ-threatening flare of systemic lupus erythematosus (SLE), characterized by proliferative lupus nephritis (acute kidney injury, proteinuria, red blood cell casts), serositis (pleuritic chest pain, friction rub, pleural effusions), and hematologic involvement (pancytopenia). The most appropriate next step in managing an acute, life-threatening SLE flare is the administration of high-dose intravenous glucocorticoids (e.g., methylprednisolone). Once the acute inflammation is controlled, a steroid-sparing immunosuppressant (e.g., cyclophosphamide or mycophenolate mofetil) will be initiated for induction therapy.

Step-by-Step Solution

Analyze the patient's clinical presentation and history.

The patient has a history of nonadherence to SLE medications and presents with a malar rash, pancytopenia, acute kidney injury with RBC casts (lupus nephritis), and pleurisy with effusions (serositis).

Identifying the underlying disease process is required to select the correct targeted therapy.

Evaluate the arterial blood gas using Winter's formula to determine if there is a mixed acid-base disorder.

Expected

pCO_2 = (1.5 \times 12) + 8 \pm 2 = 26 \pm 2

mmHg. The patient's actual

pCO_2

is 26 mmHg, indicating adequate respiratory compensation for the metabolic acidosis.

This rules out a secondary respiratory acidosis and confirms sodium bicarbonate is not urgently indicated for uncompensated respiratory failure.

Interpret the thyroid function tests and urine culture in the context of critical illness.

The low free T4 with a normal TSH in an acutely ill patient indicates euthyroid sick syndrome. The *E. coli* UTI is sensitive to narrow-spectrum agents.

This rules out the need for levothyroxine and broad-spectrum antibiotics like meropenem.

Determine the definitive treatment for the primary pathology.

The patient is experiencing a severe, organ-threatening SLE flare, requiring immediate administration of high-dose intravenous corticosteroids.

Without rapid immunosuppression, the proliferative lupus nephritis and pancytopenia will worsen and potentially become fatal.

Key Concept

Severe, organ-threatening flares of Systemic Lupus Erythematosus (such as proliferative lupus nephritis or severe serositis) require immediate treatment with high-dose intravenous glucocorticoids.

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