What is the likely diagnosis and initial management for brown vesicles surrounded by erythema?

Brown Vesicles with Redness: Diagnosis and Management

Most Likely Diagnosis

The clinical presentation of brown vesicles surrounded by erythema is most consistent with bullous impetigo, specifically in the healing phase when the flaccid bullae have ruptured and left thin brown crusts resembling lacquer. 1, 2

Key Diagnostic Features

Bullous Impetigo Characteristics

• Superficial vesicles that rapidly enlarge to form flaccid bullae filled with clear yellow fluid, which later becomes darker and more turbid 1
• After rupture, bullae leave a thin brown crust that resembles lacquer—this is the pathognomonic feature 1, 2
• Lesions are surrounded by erythema and remain well-localized but are frequently multiple 1
• Most commonly occurs on exposed areas: face and extremities 1, 2
• Regional lymphadenitis may occur, but systemic symptoms are usually absent 1, 2

Causative Organism

• Bullous impetigo is caused by Staphylococcus aureus, which produces exfoliative toxins 1
• The pathogen is usually present in the nose before causing cutaneous disease 1

Differential Diagnoses to Consider

Nonbullous Impetigo

• Begins as papules that evolve into vesicles surrounded by erythema, then become pustules that rupture to form thick honey-colored crusts (not thin brown crusts) 1, 2
• The thick, honey-colored crust is the distinguishing feature from bullous impetigo 2

Herpes Simplex Infection

• Presents with grouped, punched-out erosions or discrete vesicles, not the characteristic brown lacquer-like crusts 1
• More commonly shows multiple discrete vesicles rather than coalescing bullae 1

Contact Dermatitis (Vesicular)

• Can present with vesicles and erythema, but typically has a clear history of allergen exposure 1, 3
• Vesicles in contact dermatitis are usually smaller and more uniform, without the characteristic brown lacquer crust 3

Diagnostic Workup

Clinical Diagnosis

• The appearance of brown crusts resembling lacquer on an erythematous base is diagnostic and does not require laboratory confirmation in typical cases 1

When to Culture

• Obtain cultures of vesicle fluid, pus, or erosions to establish the causative organism if: 2
  • The patient fails to respond to initial empiric therapy
  • There is concern for methicillin-resistant S. aureus (MRSA)
  • Multiple lesions are present or during outbreaks

Initial Management

First-Line Therapy for Localized Disease

Topical mupirocin or retapamulin is as effective as oral antimicrobials and represents first-line therapy for localized impetigo 2

Indications for Systemic Therapy

Systemic antimicrobial therapy is preferred for patients with: 2

• Numerous lesions
• Outbreaks (to decrease transmission)
• Failure of topical therapy

Systemic Antibiotic Selection

First-line systemic options include: 2

• Dicloxacillin or cephalexin (e.g., cephalexin)—recommended because most S. aureus isolates from impetigo are methicillin-susceptible 2

Alternative agents for penicillin allergy or suspected MRSA: 2

• Doxycycline
• Clindamycin
• Sulfamethoxazole-trimethoprim (SMX-TMP)

Adjunctive Measures

• Incision and drainage are NOT indicated for impetigo, as this is a superficial infection without abscess formation 1
• Keep nails short to prevent autoinoculation from scratching 1
• Use dispersible cream as a soap substitute to avoid further skin irritation 1

Critical Pitfalls to Avoid

Inadequate Treatment Leading to Ecthyma

Failure to treat impetigo adequately can lead to ecthyma, a deeper infection that extends into the dermis, forming circular erythematous ulcers with adherent crusts that heal with scarring 2

Misdiagnosis as Nonbullous Impetigo

• The key distinguishing feature is the crust appearance: thin brown lacquer-like crusts indicate bullous impetigo, while thick honey-colored crusts indicate nonbullous impetigo 1, 2
• Both require similar treatment, but recognizing the bullous variant confirms staphylococcal etiology 1

Overlooking Nasal Carriage

• In patients with recurrent staphylococcal skin infections, S. aureus is usually present in the anterior nares 1
• For recurrent cases, apply mupirocin ointment twice daily in the anterior nares for the first 5 days each month, which reduces recurrences by approximately 50% 1

Unnecessary Systemic Antibiotics for Limited Disease

• Topical therapy is equally effective for localized disease and avoids unnecessary systemic antibiotic exposure 2
• Reserve systemic therapy for extensive disease or when topical therapy fails 2

When to Suspect Alternative Diagnoses

If Lesions Are Fixed for >7 Days Without Spreading

• Consider erythema multiforme, which presents with fixed targetoid lesions that persist for at least 7 days 4
• Erythema multiforme lesions are typically symmetrical on extremities (especially extensor surfaces) and do not have the brown lacquer-like crusts 4

If Deep Nodules Are Present

• Consider erythema nodosum, which presents as tender, erythematous nodules (not vesicles) that evolve from bright red to livid red/purplish to yellow/greenish, resembling a deep bruise 5
• Erythema nodosum never ulcerates and heals without scarring 5