An 18-day-old female newborn is evaluated in the pediatric emergency room after her parent… — USMLE Step 2 CK

An 18-day-old female newborn is evaluated in the pediatric emergency room after her parents noticed she was unusually difficult to arouse this morning. Over the past 2 days, she has fed poorly and felt warm to the touch. The pregnancy was complicated by a lack of prenatal care until the third trimester, but the delivery was a spontaneous vaginal birth at term. Her temperature is $38.8^\circ\text{C}$ ( $101.8^\circ\text{F}$ ), pulse is $175\text{/min}$ , and respiratory rate is $50\text{/min}$ . The infant appears lethargic and has a bulging, tense anterior fontanelle. During the physical examination, she experiences a focal clonic seizure involving the left upper extremity. Careful inspection of her skin reveals multiple scattered erythematous patches containing $1\text{-mm}$ yellow-white pustules over her trunk and proximal limbs. Lumbar puncture is performed, and cerebrospinal fluid (CSF) analysis shows the following:

Parameter	Result
Leukocyte count	$150/\text{mm}^3$ (82% lymphocytes, 18% neutrophils)
Erythrocyte count	$40/\text{mm}^3$
Protein	$180 \text{ mg/dL}$
Glucose	$50 \text{ mg/dL}$ (Serum: $85 \text{ mg/dL}$ )

Gram stain of the CSF reveals no organisms. Which of the following intravenous antimicrobial regimens is the most appropriate initial therapy for this patient?

Ampicillin, cefotaxime, and acyclovirAnswer
B
Vancomycin, cefotaxime, and acyclovir
C
Vancomycin and ceftriaxone
D
Ampicillin and cefotaxime
E
Acyclovir monotherapy

Answer

Ampicillin, cefotaxime, and acyclovir

The correct answer provides comprehensive empiric coverage for the most common causes of neonatal meningoencephalitis. Neonates (age < 28 days) with suspected meningitis require immediate coverage for Group B Streptococcus (GBS), Escherichia coli, and Listeria monocytogenes. Intravenous ampicillin provides essential coverage for Listeria (which is intrinsically resistant to all cephalosporins) and GBS. Cefotaxime covers Gram-negative organisms like E. coli as well as GBS, and has excellent CNS penetration without the kernicterus risk associated with ceftriaxone. Furthermore, this patient's focal seizures and CSF findings (lymphocytic pleocytosis with normal glucose) are highly suspicious for neonatal Herpes Simplex Virus (HSV) encephalitis. Up to 40% of neonates with HSV CNS disease do not develop a vesicular rash. Therefore, empiric intravenous acyclovir must be included until HSV PCR results return negative. The patient's pustular rash is consistent with erythema toxicum neonatorum, a benign condition requiring no targeted treatment.

Step-by-Step Solution

Identify the primary clinical syndrome.

Neonatal meningoencephalitis.

The combination of fever, lethargy, bulging fontanelle, and focal seizures in an 18-day-old infant points directly to a central nervous system infection.

Analyze the CSF indices and clinical context.

Lymphocytic pleocytosis, elevated protein, normal glucose, and focal seizures strongly suggest a viral etiology, particularly Herpes Simplex Virus (HSV).

HSV encephalitis often presents with focal neurologic deficits and a mononuclear pleocytosis. The mother's lack of early prenatal care increases the risk of undiagnosed primary genital HSV.

Evaluate the significance of the skin findings.

Erythema toxicum neonatorum.

The erythematous patches with yellow-white pustules describe a benign, transient rash common in neonates. It does not indicate a disseminated bacterial infection (like staphylococcal pustulosis).

Determine the necessary empiric antimicrobial coverage.

Regimen must cover Group B Streptococcus (GBS), E. coli, Listeria monocytogenes, and HSV.

Until definitive cultures and PCR are resulted, neonates with suspected meningitis require ampicillin (for Listeria and GBS), a third-generation cephalosporin safe for neonates like cefotaxime (for Gram-negatives and GBS), and acyclovir (for HSV).

Key Concept

Empiric treatment of neonatal meningoencephalitis

Estimated Time:1m 30s

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