What are the presentation, risk factors, and first‑line treatment for ecthyma?

Ecthyma: Presentation, Risk Factors, and First-Line Treatment

Clinical Presentation

Ecthyma presents as vesicles that rupture to form circular, erythematous ulcers with adherent crusts, often surrounded by erythematous edema, and characteristically heals with scarring. 1

Key distinguishing features include:

• Deeper skin involvement than impetigo, extending into the dermis rather than remaining superficial 1
• Punched-out ulcerations with thick, adherent crusts that develop after vesicle rupture 1
• Permanent scarring is typical, unlike impetigo which heals without scarring 1
• Most commonly affects the lower extremities, though can occur anywhere 2

Important Clinical Caveat: Ecthyma vs. Ecthyma Gangrenosum

Do not confuse typical ecthyma with ecthyma gangrenosum—these are entirely different entities:

• Ecthyma gangrenosum presents with rapidly progressive necrotic ulcers with black eschars and is associated with Pseudomonas aeruginosa bacteremia, typically in immunocompromised patients 3, 4, 5
• This life-threatening condition requires immediate antipseudomonal antibiotics and investigation for underlying immunodeficiency 3, 4
• The question refers to typical ecthyma, a streptococcal/staphylococcal skin infection 1

Risk Factors

Predisposing conditions that compromise skin integrity include:

• Pre-existing skin damage: trauma, insect bites, minor abrasions, or pre-existing impetigo 2
• Venous insufficiency or lymphatic obstruction causing chronic edema 2
• Inflammatory dermatoses such as eczema that disrupt the skin barrier 2
• Fungal infections causing fissured toe webs and maceration 2
• Poor hygiene and crowded living conditions 1
• Immunocompromised states, though typical ecthyma can occur in healthy individuals 1

First-Line Treatment

Diagnostic Approach

Obtain cultures from the ulcer base or pus to establish the causative organism and guide targeted therapy. 1 This is particularly important for ecthyma given its deeper involvement and potential for treatment failure.

Empiric Antibiotic Selection

For presumed methicillin-susceptible S. aureus (MSSA) or streptococcal infection, initiate oral dicloxacillin or cephalexin for 7 days. 1

Specific dosing:

• Dicloxacillin: 250 mg four times daily for adults 6
• Cephalexin: 250-500 mg four times daily for adults 6

When MRSA is Suspected

In areas with high MRSA prevalence or if MRSA is confirmed by culture, use doxycycline, clindamycin, or trimethoprim-sulfamethoxazole (TMP-SMX). 1

Specific dosing for MRSA coverage:

• Clindamycin: 300-450 mg three times daily for adults 6
• TMP-SMX: 1-2 double-strength tablets twice daily for adults 6

For Streptococcal Infection Alone

If cultures confirm streptococci without S. aureus, penicillin is the drug of choice; use a macrolide or clindamycin for penicillin-allergic patients. 1

Treatment Duration

Continue oral antibiotic therapy for 7 days minimum, with extension to 14 days based on clinical response and severity. 1 The deeper tissue involvement in ecthyma compared to impetigo may warrant the longer duration within this range.

Critical Treatment Pitfalls

• Never use penicillin alone empirically for ecthyma, as it lacks adequate coverage against S. aureus, which is frequently involved 6
• Topical therapy alone is inadequate for ecthyma due to its deeper dermal involvement; systemic antibiotics are always required 1
• Reassess at 3-5 days if no improvement occurs—consider MRSA resistance, non-compliance, or deeper infection than initially estimated 6
• Avoid cephalosporins in patients with type 1 hypersensitivity (anaphylaxis/hives) to penicillins 6

Special Circumstances

During outbreaks of poststreptococcal glomerulonephritis, use systemic antimicrobials to eliminate nephritogenic strains of S. pyogenes from the community. 1, 6 This public health consideration takes precedence over individual treatment decisions during such outbreaks.