Physical Examination Description of Impetigo
Impetigo presents with two distinct clinical patterns that should be systematically identified on examination: nonbullous impetigo (70% of cases) showing honey-colored crusts on an erythematous base, and bullous impetigo (30% of cases) displaying fragile, thin-roofed vesicopustules or crusted erosions with a characteristic collar of remnant roof. 1
Nonbullous Impetigo (Most Common Form)
Key examination findings to document:
- Early lesions: Erythematous papules that rapidly evolve into vesicles and pustules 1
- Classic presentation: Ruptured vesicles with dried discharge forming honey-colored crusts on an erythematous base 1
- Distribution: Typically affects the face and extremities 2
- Causative organisms: β-hemolytic streptococci, S. aureus, or both in combination 1
Bullous Impetigo
Key examination findings to document:
- Early lesions: Fragile, thin-roofed vesicopustules that form due to toxin-mediated cleavage of the dermal-epidermal junction 1
- After rupture: Crusted, erythematous erosions surrounded by a collar of remnant roof (the collapsed blister edge) 1
- Blister characteristics: Large, flaccid bullae measuring >5 mm in diameter 3
- Distribution: More likely to affect intertriginous areas 2
- Causative organism: Exclusively S. aureus producing exfoliative toxin 1
Important Clinical Distinctions
Differentiate from ecthyma (deeper infection):
- Ecthyma presents as circular, erythematous ulcers with adherent crusts
- Surrounded by erythematous edema
- Critical difference: Ecthyma heals with scarring, while impetigo does not 1
Documentation Essentials
When examining impetigo, document:
- Lesion morphology: Papules, vesicles, pustules, crusts, or erosions
- Crust characteristics: Honey-colored (pathognomonic for nonbullous) vs. other appearance
- Presence of bullae: Size, intact vs. ruptured, presence of collar remnant
- Distribution and extent: Localized (<10 lesions, <36 cm² area) vs. widespread 4
- Associated findings: Erythematous base, surrounding edema
- Depth of involvement: Superficial (impetigo) vs. deeper ulceration (ecthyma)
Common Pitfalls to Avoid
- Missing the progression: Impetigo evolves rapidly over 4-6 days from papules to crusted lesions 5
- Overlooking bullous variant: The characteristic collar of remnant roof after rupture is diagnostic 1
- Confusing with ecthyma: Check for ulceration and depth of involvement, as ecthyma requires more aggressive systemic therapy 1
- Not assessing extent: Distinguishing localized from widespread disease determines whether topical or systemic therapy is indicated 4