Ecthyma usually is caused by group A streptococcus and may complicate impetigo. Initially it is characterized by a lesion with a rim of erythematous induration surrounding an eschar, which, if removed, reveals a shallow ulcer. Ecthyma gangrenosum is a serious skin infection occurring in immunocompromised persons due to hematogenous spread of septic emboli to the skin, classically caused by Pseudomonas aeruginosa, other gram-negative organisms, or occasionally Aspergillus. The lesions begin as purple macules that undergo central necrosis to become exquisitely tender, deep, punched-out ulcers 2 to 3 cm in diameter with a dark necrotic base, raised red edges, and sometimes a yellowish green exudate. Fever usually is present.
Necrotizing fasciitis is the most extensive form of cellulitis and involves deeper subcutaneous tissues and fascial planes. It may progress to myonecrosis of the underlying muscle. Common causes include S. aureus and group A streptococcus alone or in combination with anaerobic organisms, such as Clostridium perfringens. Risk factors include underlying immunodeficiency, recent surgery or trauma, and varicella infection. Lesions progress rapidly with raised or sharply demarcated margins, although disease typically extends on a deeper plane beyond superficially evident lesions. Warning signs of necrotizing fasciitis include pain out of proportion to evident skin lesions, shock or toxic appearance, or crepitus due to subcutaneous gas formation by anaerobes. Necrotizing fasciitis is a surgical emergency, and early consultation with an experienced surgeon is recommended. Adjunctive tests such as magnetic resonance imaging can confirm the presence of gas in tissues, but obtaining imaging should not delay surgical consultation. Treatment includes rapid surgical debridement of all necrotic tissues and broad-spectrum intravenous antibiotics, such as clindamycin plus cefotaxime or ceftriaxone, with or without an aminoglycoside or vancomycin.
Folliculitis refers to small, dome-shaped pustules or erythematous papules predominantly caused by S. aureus and located in hair follicles, with superficial, limited inflammatory reaction in the surrounding tissue. Furuncles (boils) are deeper hair follicle infections that manifest as nodules with intense surrounding inflammatory reaction. These occur most frequently on the neck, trunk, axillae, and buttocks. A carbuncle represents the deepest of hair follicle infections and is characterized by multiseptate, loculated abscesses. Boils and carbuncles frequently require incisional drainage. Superficial folliculitis can be treated with topical therapy, such as an antibacterial chlorhexidine wash or an antibacterial lotion or solution such as clindamycin 1%, applied twice a day for 7 to 10 days. Oral antibiotics are necessary for unresponsive cases, or for furuncles and carbuncles.
P. aeruginosa folliculitis (hot tub folliculitis) presents as pruritic papules; pustules; or deeper, purple-red nodules predominantly on skin areas covered by a swimsuit after bathing in hot tubs. Folliculitis develops 8 to 48 hours after exposure, usually without associated systemic symptoms, and resolves in 1 to 2 weeks without treatment.
Perianal dermatitis (perianal streptococcal disease) is caused by group A streptococcus and is characterized by well-demarcated, tender, marked perianal erythema extending 2 cm from the anus. Manifestations include anal pruritus and painful defecation, sometimes with blood-streaked stools. The differential diagnosis includes diaper dermatitis, candidiasis, pin-worm infection, and anal fissures. Treatment is oral penicillin or cefuroxime.
Available @ StudentConsult.com