By Gary M. White, MD
Cellulitis is a rapidly expanding bacterial infection of the skin. Impetigo is also a bacterial infection of the skin but is primarily confined to the superficial layers. Cellulitis involves deeper layers of the skin including the dermis. Erysipelas is a specific subset of cellulitis caused by streptococcus.
Clinically, one sees a warm, edematous, expanding plaque. The face and lower legs are common sites. On the lower legs, confusion with stasis dermatitis often occurs.
Necrotizing fasciitis is a more severe infection that can be life-threatening. It may be suspected when there are systemic signs (e.g., fever, chills) or if the skin shows more than just erythema and edema, e.g., bulla, hemorrhage, necrosis, or fluctuance.
Non-dermatologists commonly misdiagnose patients as having cellulitis. Diagnoses most commonly confused with cellulitis include stasis dermatitis, contact dermatitis, tinea pedis, drug eruption and psoriasis [JAAD 2015;73;70].
The diagnosis is usually made clinically. Any drainage should be cultured. In the absence of drainage, skin-biopsy specimens even with PCR and pyrosequencing, are usually unhelpful [Clin Infect Dis 2015 Aug 3].
The main bacteria responsible for cellulitis are Streptococcus and Staphylococcus. MRSA causing cellulitis is increasing. If the cellulitis is localized and uncomplicated, the patient may be treated with oral or IV antibiotics and followed closely. If there is a suspicion of necrotizing fasciitis, evaluation by a surgeon or an infectious disease or other specialist is in order. Imaging (e.g., MRI) can be helpful in some cases in detecting involvement of deeper tissue.
Consultation with an infectious disease specialist should be obtained, but in the past, the following have been used in milder cases where oral antibiotics are appropriate. Treat for five days. If no better, reassess and extend treatment.
Cessation of lesion spread and improvement of local inflammation after 24 hours of treatment is associated with treatment success.
In one study of patients with 3 or more episodes of cellulitis of the lower leg, penicillin 250 BID reduced cellulitis by about 50% while on treatment. The effect went away when stopped.
Another report showed an approximate 75% reduction in cellulitis over the course of a year in patients with chronic lymphedema using an advanced pneumatic compression device (Flexitouch System) [JAMA Derm 2015;151;1183].
Two different patients. Same cellulitis.
Infection of a surgical wound 4 days post-op.
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