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INFECTIONS OF THE SKIN

IMPETIGO

ESSENTIALS OF DIAGNOSIS

  • Nonbullous: yellowish crusted plaques.

  • Bullous: bullae, with minimal surrounding erythema, rupture to leave a shallow ulcer.

General Considerations

Impetigo is a bacterial infection of the skin. More than 70% of cases are of the nonbullous variety.

Pathogenesis

Most cases of nonbullous impetigo are caused by Staphylococcus aureus, although group A β-hemolytic streptococci are found in some cases. S aureus that produces exfoliative toxin is the cause of bullous impetigo; methicillin-resistant S aureus (MRSA) has been isolated from patients. Impetigo can develop in traumatized skin, or the bacteria can spread to intact skin from its reservoir in the nose.

Clinical Findings

Nonbullous impetigo usually starts as a small pustule or vesicle that ruptures easily, followed by the classic small (<2-cm), honey-colored, crusted plaque. The infection may be spread to other parts of the body by fingers or clothing. There is usually little surrounding erythema, itching occurs occasionally, and pain is usually absent. Without treatment, the lesions resolve without scarring in 2 weeks.

Bullous impetigo is usually seen in infants and young children. Lesions begin on intact skin on almost any part of the body; common locations include the diaper area, axillae, and skin folds. Flaccid, thin-roofed vesicles develop, which rupture to form shallow ulcers with surrounding “collarette” of scale.

Differential Diagnosis

Nonbullous impetigo is unique in appearance. Bullous impetigo is similar in appearance to pemphigus and bullous pemphigoid. Growth of staphylococci from fluid in a bulla confirms the diagnosis.

Complications

Cellulitis follows ~10% of cases of nonbullous impetigo but rarely follows bullous impetigo. Either type may rarely lead to septicemia, septic arthritis, or osteomyelitis. Scarlet fever and poststreptococcal glomerulonephritis, but not rheumatic fever, may follow streptococcal impetigo. Treating impetigo has not been shown to prevent poststreptococcal glomerulonephritis.

Treatment

Localized disease is effectively treated with topical 2% mupirocin or 1% retapamulin ointment for 5 days. Ozenoxacin 1% cream is a newer, second-line option. Patients with widespread lesions or evidence of cellulitis should be treated with systemic antibiotics effective against staphylococci and streptococci. If infection with MRSA is a possibility, trimethoprim-sulfamethoxazole or clindamycin should be considered; fluoroquinolones must not be used due to risks of widespread MRSA resistance and musculoskeletal adverse effects.

Patient Education

Further information is available at the following link: https://kidshealth.org/en/parents/impetigo.html.

FUNGAL INFECTIONS

General Considerations

Fungal infections of the skin and skin structures may be generally grouped into three categories: dermatophyte infections, other tinea infections, and candidal infections.

Pathogenesis

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