A 44 year old female presented to a community emergency department complaining of an abscess on her lateral right thigh that had been increasing in size for the last 2 days. She reported having been kicked in that leg a few days prior. She had been not been febrile, but did report some generalized malaise. Her medical history was remarkable for chronic Hepatitis C without cirrhosis and a remote history of IV drug use, though patient strongly denied any recent use and had no apparent active injection marks. Physical exam showed a 4 cm abscess on the lateral right thigh, roughly 2/3 of the way between the greater trochanter and the knee, with about 10 cm of associated cellulitis. Incision and drainage was performed and the patient was prescribed analgesics and trimethoprim/sulfamethoxazole. The margins of the cellulitis were marked and the patient was instructed to follow up for wound check the following day.
On returning to the ED, the patient noted that she had copious thin drainage from the wound, saturating several dressings. Physical exam was remarkable for large extension of the cellulitic region, which was then extending proximally to roughly the inguinal ligament and involving the entire posterior thigh as well, as far proximal as the gluteal crease. There was no crepitus on exam. The region was now exquisitely tender to even light palpation, but when not being examined, the patient seemed remarkably unconcerned with the condition of her leg. Laboratory studies were performed, showing a sodium level of 137 mg/dL, creatinine 0.7mg/dL, glucose (nonfasting) 107 mg/dL, C-reactive protein 179mg/L, haemoglobin 6.7 g/dL and white blood cell count of 25,600/ml.
She was started on broad spectrum antibiotic coverage with vancomycin, levofloxacin and piperacillin/tazobactam and admitted to the medical ICU with surgical consultation, then transferred to the regional burn center at Janus General Hospital(1) with high clinical suspicion for necrotizing fasciitis. On arrival, clindamycin was added to the antimicrobial regimen and the patient was taken urgently to the operating suite.
Upon examination under anaesthesia, it was noted that tissue planes surrounding the existing abscess incision could be divided easily with a gloved finger, and with minimal effort, the surgeon could wrap his finger around the femur through the existing incision. Wide debridement was performed, which demonstrated extensive adipositis, fasciitis, myositis and osteomyelitis. Excision was carried to the level of healthy bleeding tissue, which involved excision of roughly 50% of the soft tissues of the thigh on her initial surgery, and ultimately a right hip disarticulation amputation on second-look procedure the following day. Wound cultures grew large amounts of a single organism, Staphylococcus aureus resistant to oxacillin. The patient ultimately required daily debridements of small amounts of further necrotic muscle tissue, but did not require further bony resection such as hemipelvectomy.
Necrotizing soft tissue infections (NSTI, which encompasses fasciitis and myositis) are fairly uncommon, but thoroughly devastating and often fatal when they occur. While there is a validated scoring system based on lab values (2), the negative predictive value for a cutoff score of 6 is only 96%, and thus NSTI remains a clinical and ultimately surgical diagnosis. The patient presented above had a LRINEC score of 8 on initial presentation, which reportedly has a positive predictive value of over 93% for the diagnosis (2).
Concerning clinical features are pain out of proportion to exam findings, rapid advancement of cellulitic (or especially necrotic) skin changes and crepitus on palpation (though this is only found when the infection involves a gas-forming organism such as Clostridium). If an abscess is found and incision and drainage is performed, expression of more purulent material than expected, a runny “dishwater-like” consistency of the drainage and especially ease in dividing tissue planes would also significantly raise one’s clinical suspicion for NSTI. An inconsistently reported finding is “la belle indifference,” in which the patient seems unconcerned with or unable to understand the severity of the infection (3).
Treatment requires surgical intervention (4). Due to the extensive nature of the soft tissue defects left after appropriate surgery, referral to a regional burn center is often appropriate (5). Because the necrotizing nature of the infection destroys microvascular structures, antibiotic penetration into the involved tissues is woefully inadequate and pharmacologic therapy alone would be expected to fail. Antibiotics are, of course, a necessary adjunct and should be directed against the expected pathogens: Streptococcus species and anaerobes such as Clostridium are the classical etiologic agents, with S. aureus (especially methicillin-resistant isolates)(6) emerging as an increasingly common cause as well. Thus, an appropriate antibiotic regimen would include an extended spectrum beta lactam with anaerobic coverage, such as piperacillin/tazobactam, and antistaphylococcal coverage such as vancomycin, linezolid or daptomycin. Clindamycin is classically used as an adjunctive antimicrobial due to its inhibitory effect on the bacterial 50S ribosome, thereby reducing production and release of streptococcal toxins, but it bears repeating that the choice of antimicrobial agents is insignificant in comparison to rapid surgical management (7).
2) Wong CH, et al. The LRINEC (Laboratory Risk Indicator for Necrotizing Fasciitis) score: a tool for distinguishing necrotizing fasciitis from other soft tissue infections. Crit Care Med. 2004 Jul;32(7):1535-41.
3) Herbert M and Swadron S (January 2009) EM:RAP [Audio Podcast] Retrieved from http://www.emrap.org
4) Kelly EW and Magilner D (2011). Soft Tissue Infections. In Tintanalli J (Ed) Tintanalli’s Emergency Medicine, A comprehensive study guide (7th Ed). 1020-21. New York, NY: McGraw-Hill
5) Barillo DJ. Burn center management of necrotizing fasciitis. J Burn Care Rehabil. 2003 May-Jun;24(3):127-32.
6) Miller LG, et al. Necrotizing Fasciitis Caused by Community-Associated Methicillin-Resistant Staphylococcus aureus in Los Angeles N Eng J Med. 2005;352:1445-53
7) Stevens DL, et al. Practice guidelines for the diagnosis and management of skin and soft tissue infections. Clin Infect Dis. 2005; 41(10):1373-1406