What is the cause and treatment for a 15-day-old newborn with bony swelling behind the ear and small pustules above it?

Diagnosis and Management of Bony Swelling Behind the Ear with Pustules in a 15-Day-Old Newborn

This presentation is most consistent with mastoiditis with overlying skin infection, which requires immediate medical evaluation, hospitalization, and intravenous antibiotics, as neonates can rapidly progress from localized infection to life-threatening sepsis. 1

Immediate Assessment Required

This clinical presentation demands urgent evaluation because:

• Neonates under 2 weeks old can deteriorate rapidly from localized skin infections to sepsis 1
• The bony swelling behind the ear suggests possible mastoiditis or underlying bone involvement 1
• Small pustules indicate bacterial skin infection that can serve as a portal for deeper infection 1
• Signs of serious illness in neonates include loss of alertness, poor feeding, high-pitched cry, and lethargy—all of which should be actively assessed 2

Critical Management Steps

1. Immediate Hospitalization and Cultures

• Bacterial cultures must be obtained from the pustules and blood before initiating antibiotics to guide definitive therapy 1
• Regular bacterial swabs from affected areas should be performed 1
• The neonate requires close monitoring for fever, lethargy, poor feeding, and signs of systemic illness 1

2. Empiric Intravenous Antibiotic Therapy

Cefalexin is absolutely contraindicated in neonates as pediatric dosing guidelines specifically exclude this age group (birth to 28 days) 1

Appropriate first-line antibiotics for suspected staphylococcal/streptococcal infections include:

• Nafcillin or oxacillin at 50 mg/kg/dose every 6 hours IV for suspected staphylococcal infection 1
• Penicillin G at 100,000-150,000 units/kg/day IV in divided doses every 4-6 hours for penicillin-susceptible organisms 1
• Empiric broad-spectrum coverage may be needed initially, with de-escalation based on culture results 1

3. Local Wound Care

While systemic antibiotics are the priority, appropriate local care includes:

• Gently cleanse pustules with antimicrobial solution, taking care not to rupture them initially 3
• Pierce pustules at the base with a sterile needle if drainage is needed, applying gentle pressure with sterile gauze 3
• Do not deroof the blisters/pustules 3
• After drainage, cleanse again with antimicrobial solution 3
• Apply nonadherent dressing as needed 3

4. Monitoring for Complications

Key warning signs requiring immediate escalation:

• Marked retraction of lower ribs, high-pitched or moaning cry, expiratory grunt 2
• Loss of alertness, central cyanosis, severe hypotonia 2
• Fluid intake less than one-third of normal, convulsions, bile-stained vomiting 2
• Extension of erythema or swelling 1

Important Caveats

• Prophylactic antibiotics are generally not recommended but may be considered in high-risk neonatal situations 1
• The bony swelling requires imaging evaluation (likely CT or MRI) to assess for mastoiditis or osteomyelitis, though this should not delay antibiotic initiation 1
• Neonatal infections can progress to sepsis within hours, making aggressive supportive care essential alongside antimicrobial therapy 4
• Any additional stress during the first weeks of life can result in significant morbidity and mortality 4

Differential Considerations

While mastoiditis with skin infection is most likely, other considerations include:

• Congenital lesions with secondary infection (though less likely given the acute presentation with pustules) 3, 5
• Birth trauma with subsequent infection 6
• Underlying bone abnormality with overlying cellulitis 6

The combination of bony swelling and pustules in a 15-day-old neonate constitutes a medical emergency requiring immediate hospital admission and IV antibiotics—outpatient management is inappropriate for this age group and presentation. 1