Paronychia. (Photo contributor: Lawrence B. Stack, MD.)
Cellulitis is a common infection of the skin or subcutaneous tissues with characteristic findings: erythema with poorly defined borders, edema, warmth, pain, and limitation of movement. Fever and constitutional symptoms may be present and are commonly associated with bacteremia. Predisposing factors include trauma, lymphatic or venous stasis, immunodeficiency (including diabetes mellitus), and foreign bodies. Common etiologic organisms include group A β-hemolytic Streptococcus and Staphylococcus aureus in nonintertriginous skin, and gram-negative organisms or mixed flora in intertriginous skin and ulcerations. In immunocompromised hosts, Escherichia coli, Klebsiella species, Enterobacter species, and Pseudomonas aeruginosa are common. In recent years, there has been a dramatic increase in the incidence of community-acquired methicillin-resistant S aureus (CA-MRSA), particularly in cellulitis associated with a cutaneous abscess. The differential diagnosis includes deep venous thrombosis (DVT), venous stasis, erythema nodosum, septic or inflammatory arthritis/bursitis, and allergic reactions.
Cellulitis. Cellulitis of the left leg characterized by erythema and mild swelling. (Photo contributor: Frank Birinyi, MD.)
Management and Disposition
Treatment of minor cases commonly consists of immobilization, elevation, analgesia, and oral β-lactam antibiotics with reevaluation in 48 hours. The increase in the incidence of CA-MRSA has prompted some, especially in highly endemic areas, to advocate coverage with trimethoprim/sulfamethoxazole or other agents (refer to current recommendations) in addition to conventional β-lactam antibiotics. Admission and parenteral administration of antibiotics may be necessary for immunocompromised or toxic-appearing patients, or those who do not respond to outpatient therapy.
Rapidly progressive cellulitis or one that progresses despite treatment with β-lactam antibiotics should raise suspicion for CA-MRSA or deeper infections such as fasciitis.
Known risk factors for CA-MRSA include military personnel, prison inmates, and competitive sports players.
Routine blood or leading-edge cultures in nontoxic patients are generally low yield.
Cellulitis. Cellulitis of the right lower extremity characterized by sharply demarcated erythema and edema. (Photo contributor: Robert Tubbs, MD.)
A felon is a pyogenic infection of the distal digital pulp space, with pus collecting in the spaces formed by the vertical septa anchoring the pad to the distal phalanx. This condition is characterized by severe pain, exquisite tenderness, and tense swelling of the distal digit with erythema. There may be a visible collection of pus or palpable fluctuance. Complications include deep ischemic necrosis, osteomyelitis, septic arthritis, and suppurative tenosynovitis. The differential diagnosis includes paronychia, herpetic whitlow, and hematoma following traumatic injury.