How should I evaluate and manage a crusted skin lesion?

Evaluation and Management of Crusted Skin Lesions

Obtain a biopsy or aspiration of any crusted lesion that is nonhealing, rapidly growing, or atypical to establish a definitive diagnosis before initiating treatment, as the differential diagnosis is broad and includes both infectious and non-infectious etiologies that require vastly different management approaches. 1

Initial Clinical Assessment

When evaluating a crusted skin lesion, systematically assess for these specific features:

• Duration and progression: Wounds lasting >4 weeks, rapidly enlarging lesions, or those with altered sensation (tingling, increased pain) suggest malignancy or atypical infection 1
• Morphology: Honey-colored crusting indicates impetigo (Staphylococcus aureus or Streptococcus pyogenes), while thick adherent crusts with pustules suggest kerion (inflammatory tinea capitis) 1, 2
• Distribution: Exposed areas favor impetigo or ecthyma; axillary/perineal locations increase concern for polymicrobial infection 1
• Associated findings: Regional lymphadenopathy, systemic symptoms (fever, chills), or multiple lesions alter management urgency 1

Diagnostic Approach

The cornerstone of diagnosis is obtaining tissue for histological and microbiological evaluation—this should be implemented as an early diagnostic step, not after empiric treatment failure. 1

Specimen Collection Techniques

• For suspected infection: Use blunt scalpel to remove crust, scale, and underlying tissue; pluck hairs if scalp involvement 1
• For suspected malignancy: Full-thickness punch or excisional biopsy of the most indurated or suspicious area 1
• Send specimens for: Gram stain, bacterial culture, fungal culture (with KOH prep), and histopathology 1

A critical pitfall is treating empirically without tissue diagnosis—this delays appropriate therapy and can mask serious conditions like squamous cell carcinoma, which in high-risk populations (e.g., epidermolysis bullosa) presents as nonhealing crusted wounds indistinguishable from benign ulceration. 1

Differential Diagnosis Framework

The differential must simultaneously consider infectious and non-infectious etiologies:

Infectious Causes

• Bacterial: Impetigo (honey-colored crust), ecthyma (deep ulceration with crust), secondary infection of wounds 1, 3
• Fungal: Kerion (boggy mass with thick crust and pustules), favus (T. schoenleinii with yellow cup-shaped crusts) 1
• Viral: Varicella zoster (requires firm adherent crust with no new lesions before sports clearance) 1

Non-Infectious Causes

• Drug eruption, malignancy infiltration, chemotherapy/radiation reactions, Sweet syndrome, erythema multiforme, leukocytoclastic vasculitis 1
• Squamous cell carcinoma: Presents as hyperkeratotic crusted lesions with raised edges, especially in chronic wounds 1

Initial Management Pending Diagnosis

While awaiting biopsy results, initiate conservative wound care:

• Cleanse gently with sterile normal saline—avoid iodine or antibiotic solutions unless specifically indicated 3, 2
• Apply nonadherent dressings to reduce bacterial superinfection and pain 3
• For intact blisters: Leave in place; for large blisters, drain while preserving the roof as a natural dressing 3
• Document thoroughly: Photograph lesions, measure size, note exact location 3, 4

When to Start Empiric Antimicrobial Therapy

Initiate topical mupirocin 2% ointment if clinical features strongly suggest bacterial infection (purulent exudate, pustules, honey-colored crusting, rapid progression with warmth and erythema) while awaiting culture results. 3, 2, 4

Consider systemic antibiotics immediately if:

• Extensive surrounding cellulitis or multiple lesions 1, 3
• Systemic symptoms (fever, malaise) 3, 2
• Immunocompromised host 1
• Deep tissue involvement or cutaneous gangrene 1

For immunocompromised patients, the threshold for biopsy and systemic therapy is lower because localized lesions may represent disseminated or life-threatening infection. 1

Treatment Based on Confirmed Diagnosis

Bacterial Infections

• Localized impetigo: Topical mupirocin 2% TID for 5-7 days 3, 4
• Extensive disease: Oral cephalexin or dicloxacillin; consider MRSA coverage (trimethoprim-sulfamethoxazole, doxycycline, or clindamycin) based on local resistance patterns 1, 2
• Furuncles/carbuncles: Incision and drainage is primary treatment; antibiotics only if extensive cellulitis or systemic symptoms 1

Fungal Infections

• Kerion: Systemic antifungal therapy (griseofulvin or terbinafine) for 6-12 weeks; topical therapy alone is insufficient 1
• Superficial candidiasis: Topical azoles (clotrimazole, ketoconazole) 2

Varicella Zoster

• Lesions must have firm, adherent crust with no new lesions for 48 hours before returning to contact activities 1
• Consider systemic antivirals if presenting within 72 hours of rash onset 1

Red Flags Requiring Urgent Specialist Consultation

• Nonhealing wound >4 weeks despite appropriate therapy (consider malignancy) 1
• Rapidly progressive lesions with systemic toxicity (consider necrotizing infection) 1
• Immunocompromised patients with atypical presentations (broader differential including opportunistic pathogens) 1
• Suspected Stevens-Johnson syndrome/TEN (skin sloughing >30% BSA requires immediate hospitalization) 2

Monitoring and Follow-Up

• Reassess within 48-72 hours if empiric therapy initiated 3
• Change dressings when soiled using aseptic technique 3
• Elevate affected area if swollen to accelerate healing 3
• Instruct patients to seek immediate care if increasing pain, redness, swelling, or fever develops 3, 4

The key principle is that crusted lesions represent a diagnostic challenge requiring tissue diagnosis in most cases—clinical appearance alone is insufficient to distinguish between infectious, inflammatory, and neoplastic processes that demand fundamentally different treatments. 1