Skin and soft tissue infections
- Impetigo
- Herpes zoster infection (shingles)
- Reactivation of varicella-zoster virus infection; incidence increases with age
- Erythematous macules present in unilateral dermatomal distribution, preceded by prodromal paresthesias or pain
- Macules progress to painful vesicles, which may become bullous or hemorrhagic
- Differentiating features include dermatomal distribution and presence of pain, combined with history of prodromal skin sensation
- Diagnosis is usually clinical but can be confirmed by polymerase chain reaction for varicella-zoster virus
- Varicella (chickenpox) (Related: Varicella (chickenpox) infection)
- Thin-walled vesicles on erythematous base occur on face, trunk, and extremities
- Vesicles break and lead to crust formation, which may resemble impetigo, especially if there is secondary bacterial infection
- Generally more diffuse than impetigo, and characterized by crops of highly pruritic lesions in different stages occurring simultaneously
- Diagnosis is usually clinical but can be confirmed by immunohistochemistry, enzyme immunoassay, or polymerase chain reaction to detect varicella-zoster virus in vesicle fluid or scrapings
- Herpes simplex (Related: Genital herpes infection)
- Grouped vesicles that ulcerate and crust within 48 hours; usually in orofacial or genital locations
- Pain, burning, itching, and/or tingling are present as a prodrome
- There may be a history of previous outbreaks in the same anatomic location
- Diagnosis is usually clinical but can be confirmed by direct fluorescent antibody testing or polymerase chain reaction on scrapings from vesicle base
- Atopic dermatitis (atopic eczema) (Related: Eczema and atopic dermatitis)
- Common inflammatory skin disorder with itching and inflammation often related to an environmental exposure
- Usually occurs in setting of family and/or personal history of allergic rhinitis and asthma
- Pruritic areas of redness and edema appear; tiny vesicles may be present
- Lichenification of the flexures is a common finding; in children, the face, neck, and trunk are primarily affected
- Diagnosis is determined with history, physical examination, and skin patch testing
- Tinea corporis (ringworm) (Related: Tinea infections)
- Annular lesions with an advancing, scaly border, located on the face, trunk, or extremities; caused by Trichophyton or Microsporum species
- Central clearing occurs as borders of lesions extend outward
- Lesions may be pustular, hypopigmented, or minimally elevated
- Secondary bacterial infection of tinea corporis often mimics impetigo
- Diagnosis is usually clinical, but microscopy of a wet mount with potassium hydroxide can confirm diagnosis
- Herpes zoster infection (shingles)
- Cellulitis (due to community-acquired MRSA)
- Spider bite
- Recluse spider bites (found in midwestern and southern parts of United States) may appear as an area of necrosis at site of bite, surrounded by erythema (Related: Brown recluse envenomation)
- Proximal lymphadenopathy may be present
- Rare condition, and reports of spider bite may be unreliable
- Accurate differentiation may not be possible unless spider was observed biting or recovered for identification
- Erythema chronicum migrans
- Lyme disease
- Differentiate by history (including travel to or residence in an endemic area) and physical examination, with the characteristic appearance and subacute evolution of the erythema chronicum migrans rash
- In an endemic setting, characteristic appearance of the rash is considered diagnostic. Lyme serology results are often negative at presentation of rash
- Spider bite