Skin-nontumor / Clinical Dermatology

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Skin-nontumor / Clinical Dermatology

Blistering disorders

Bullous impetigo

Reviewer: Mowafak Hamodat, MB.CH.B, MSc. (see Reviewers page)
Revised: 26 August 2011, last major update July 2011
Copyright: (c) 2002-2011, PathologyOutlines.com, Inc.

Description
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● Impetigo is due to bacterial infection of superficial epidermis, most common in infants and children
● Either primary infection due to bacterial invasion through minor breaks in skin, or secondary infection of preexisting dermatosis or infestation
● Bullous form of impetigo has confluent pustules with honey-colored crusts, usually on face, trunk, buttock, perineum or extremities; nonbullous form also exists
● See also impetigo

Etiology
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● Due to impetigo (Staphylococcus aureus infection) and its exfoliative toxins A and B, which target desmoglein 1, a desmosomal adhesion molecule in upper epidermis (J Dermatol Sci 2008;49:21)
● Community acquired methicillin-resistant S. aureus is common (Cutis 2010;85:65)
● In non-Western countries, Streptococcus pyogenes is an important cause (PLoS Negl Trop Dis 2009;3:e467)
● Highly contagious, may be spread by asymptomatic healthcare workers (J Hosp Infect 2007;67:264)
● Simple impetigo may occur in endemic or epidemic form and spread to involve siblings and schoolmates

Drawings
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Desmoglein 1 (Dsg1)

Clinical features
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● Confluent pustules with honey-colored crusts, usually on face, trunk, buttock, perineum or extremities
● Vesicles rapidly enlarge and become flaccid transparent bullae up to 5 cm, containing clear yellow to dark yellow / turbid fluid
● Margins are sharply demarcated without erythema
● Negative Nikolsky sign (sheet-like removal of epidermis with sliding pressure)
● Highly contagious; may occur in outbreaks (Antonie Van Leeuwenhoek 2009;95:387, Euro Surveill 2009;14:19372)
● May affect caregivers (Cutis 2008;81:115)
● Usually indicates penicillin resistance
● Risk factors include skin abrasions, trauma, burns, poor hygiene, insect bites, diabetes mellitus, primary varicella infection, eczema, atopic dermatitis; also carriers of Staphylococcal aureus in nose or perineum (Can Fam Physician 2008;54:193)
● Diagnosis is usually clinical; can also culture blister fluid; obtain blood cultures if systemic; biopsies are uncommon
● May overlap with blistering distal dactylitis - acral oval bullae 10-30 mm in diameter (Clin Exp Dermatol 2007;32:314)

Treatment and prognosis
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● Local treatment with 2% mupirocin ointment or fusidic acid plus local care (cleansing, removal of crusts, application of wet dressings - Am Fam Physician 2007;75:859, eMedicine #1, #2)
● Up to 50% of strains of S. aureus may be resistant to fusidic acid (Acta Derm Venereol 2010;90:52, Clin Exp Dermatol 2009;34:136)
● Disease is usually self-limited, but treatment relieves discomfort, improves cosmetic appearance, prevents spread of organism that also causes glomerulonephritis and other illnesses
● Complicated or diffuse disease (staphylococcal scalded skin syndrome) requires 5-10 days of beta-lactamase resistant antibiotics (cephalexin, amoxicillin and clavulanate); erythromycin may be effective in communities with low levels of penicillin resistance
● Complications include lymphadenitis, cellulitis, glomerulonephritis and sepsis

Clinical images
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Various images

Abdomen

Micro description
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● Cleavage plane is subcorneal or upper granular layer
● Variable acantholysis
● Pustule is filled with neutrophils, and bacterial clusters are evident with Gram stain
● The underlying dermal infiltrate contains a mixed neutrophil and lymphocytes infiltrate; neutrophils may be seen in the spongiotic stratum spinosum

Micro images
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Subcorneal blister with inflammatory cells

Differential diagnosis
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● Herpes simplex infection: different clinical history, viral inclusions
● Allergic contact dermatitis: different clinical history, extensive spongiosis, numerous eosinophils
● Thermal burns: different clinical history
● Insect bites: different clinical history
● Other blistering disorders, including chronic bullous dermatosis of childhood (J Telemed Telecare 2009;15:208)
● Superficial variant of pemphigus, particularly as the latter become secondarily infected and there may be one or two acantholytic cells in impetigo
● Antibodies in a pemphigus like pattern may be demonstrated in Bullous impetigo and distinction from pemphigus foliaceous may therefore be a problem; generally the presence of numerous neutrophils and the recognition of Gram’s positive cocci is sufficiently characteristic of impetigo, as acantholytic cells are very scanty
● Subcorneal pustular dermatosis and pustular psoriasis may be considered in the differential diagnosis

End of Skin-nontumor / Clinical Dermatology > Blistering disorders > Bullous impetigo

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