What is the diagnosis and treatment for a skin lesion that starts as erythema and itchy vesicles, ruptures, and forms a crust?

Diagnosis: Impetigo (Nonbullous)

The clinical presentation of erythema progressing to itchy vesicles that rupture and form crusts is diagnostic of nonbullous impetigo, a superficial bacterial skin infection caused by Staphylococcus aureus and/or β-hemolytic streptococci. 1

Clinical Features

• Nonbullous impetigo begins as erythematous papules that rapidly evolve into vesicles and pustules, which then rupture to form characteristic honey-colored crusts on an erythematous base 1
• The lesions typically occur on exposed areas of the body, most frequently the face and extremities 1
• Itching (pruritus) is a common feature, distinguishing this from other vesicular conditions 2
• Regional lymphadenitis may occur, but systemic symptoms are usually absent 1

Treatment Recommendations

For Limited Disease (Few Lesions)

Topical mupirocin or retapamulin is as effective as oral antimicrobials and represents first-line therapy for localized impetigo 1

• Debride crusts before applying topical antibiotics to improve penetration 2
• Local cleansing with gentle removal of crusts is fundamental to treatment 2

For Extensive Disease (Multiple Lesions or Outbreaks)

Systemic antimicrobial therapy is preferred for patients with numerous lesions or during outbreaks to decrease transmission 1

First-line systemic options:

• Dicloxacillin or cephalexin (e.g., first-generation cephalosporins) are recommended because most S. aureus isolates from impetigo are methicillin-susceptible 1

Alternative agents (for penicillin allergy or suspected MRSA):

• Doxycycline 1
• Clindamycin 1
• Sulfamethoxazole-trimethoprim (SMX-TMP) 1

If cultures yield streptococci alone:

• Penicillin is the drug of choice 1
• Macrolide or clindamycin for penicillin-allergic patients 1

Diagnostic Confirmation

• Cultures of vesicle fluid, pus, or erosions establish the causative organism 1
• Unless cultures yield streptococci alone, antimicrobial therapy should be active against both S. aureus and streptococci 1

Important Differential Diagnoses to Exclude

Bullous impetigo differs by presenting with larger, flaccid bullae (>5mm) that rupture leaving thin brown crusts resembling lacquer, rather than the thick honey-colored crusts of nonbullous impetigo 1

Contact dermatitis can occasionally present with vesicles and erythema, but typically lacks the characteristic honey-colored crusting and may have unusual bullous presentations 3

Tinea corporis presents with well-demarcated, circular, scaly patches with raised leading edges and satellite lesions, rather than honey-colored crusts 4

Clinical Pitfalls

• 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 1
• Do not confuse with herpes simplex, which typically presents with grouped vesicles on an erythematous base but lacks the honey-colored crusting 5
• Bacterial superinfection can complicate other conditions (such as zinc deficiency), making diagnosis challenging 6