What is ecthyma, and how is it diagnosed and managed?

What is Ecthyma?

Ecthyma is a deeply ulcerated form of impetigo that extends through the epidermis into the dermis, presenting as vesicles that rupture to form circular, erythematous ulcers with adherent crusts and surrounding edema, healing with scarring. 1, 2

Clinical Presentation

• Lesion characteristics: Begins as papules that rapidly evolve into vesicles surrounded by erythema, then become pustules that enlarge and break down over 4-6 days to form thick crusts 1
• Depth of involvement: Unlike superficial impetigo, ecthyma penetrates deeper into the dermis, creating ulcerated lesions 1
• Location: Typically occurs on exposed areas of the body, most frequently the face and extremities 1
• Healing pattern: Lesions heal slowly and leave depigmented areas and scarring 1, 2
• Associated findings: Regional lymphadenitis may occur, though systemic symptoms are usually absent 1

Important Distinction: Ecthyma vs. Ecthyma Gangrenosum

These are completely different entities that should not be confused:

• Ecthyma gangrenosum is a cutaneous vasculitis caused by bacterial invasion of vessel walls, beginning as painless erythematous macules that rapidly become painful and necrotic within 12-24 hours 1
• Classically associated with Pseudomonas aeruginosa bacteremia in neutropenic/immunocompromised patients, though can occur with other organisms 1, 3
• Presents preferentially in the groin, axilla, or trunk and can increase from 1 cm to >10 cm in <24 hours 1

Diagnosis

Obtain cultures of vesicle fluid, pus, erosions, or ulcers to establish the causative organism. 2

Diagnostic Approach:

• Gram stain and culture of pus or lesion material to guide targeted therapy 2
• Microbiology: Colonization with streptococcal strains precedes impetiginous lesions by a mean of 10 days; inoculation occurs through abrasions, minor trauma, or insect bites 1
• Pathogen patterns: In streptococcal ecthyma, organisms transfer from skin to upper respiratory tract over 2-3 weeks; in staphylococcal disease, pathogens are usually present in the nose before causing cutaneous disease 1

Management

For presumed methicillin-susceptible S. aureus (MSSA), use dicloxacillin or cephalexin for 7 days. 2

Treatment Algorithm:

Step 1: Empiric Therapy Based on Local MRSA Prevalence

• High MRSA prevalence areas: Start empiric coverage for MRSA with doxycycline, clindamycin, or sulfamethoxazole-trimethoprim (SMX-TMP) until culture results available 2
• Low MRSA prevalence: Start with dicloxacillin or cephalexin 2

Step 2: Adjust Based on Culture Results

• MRSA confirmed: Continue doxycycline, clindamycin, or SMX-TMP 2
• MSSA confirmed: Switch to or continue dicloxacillin or cephalexin 2
• Streptococci alone: Penicillin is the drug of choice; use macrolide or clindamycin for penicillin-allergic patients 2

Step 3: Duration

• Standard duration: 7 days of oral antibiotic therapy 2
• Range for bacterial skin infections: 7-14 days depending on clinical response 2

Special Circumstances:

Outbreaks of poststreptococcal glomerulonephritis:

• Use systemic antimicrobials to eliminate nephritogenic strains of S. pyogenes 2

Common Pitfalls to Avoid:

• Do not confuse ecthyma with ecthyma gangrenosum - the latter requires immediate antipseudomonal antibiotics and evaluation for sepsis in immunocompromised patients 1, 3
• Do not skip cultures - establishing the causative organism is essential for targeted therapy, especially given variable MRSA prevalence 2
• Do not undertreate - the deeper dermal involvement requires full systemic antibiotic course, not just topical therapy 1, 2