Cellulitis

Learning objectives:
Review the differential of Cellulitis
Summarize management of Cellulitis in Diabetics
Discuss Necrotizing Fascitis diagnosis, management

#1. Differential of Cellulitis
Includes Infectious Processes:
necrotizing fasciitis, gas gangrene, toxic shock syndrome, bursitis, osteomyelitis, herpes zoster, and erythema migrans

And NonInfectious Processes:
contact dermatitis, deep venous thrombosis, acute gout, drug reactions, insect stings, and malignancy, thermal burn (sjs/ten), pemphigus
* history should include inquiry into exposures, drug history, insect bites, trauma, water exposure, occupation (fish-handler), immune state, h/o MRSA or close contacts with MRSA, topical lotions/cosmetics, hot tub exposure

#2.Management of DM cellulitis is based on severity
1. Superficial diabetic foot wounds are often due to aerobic gram-positive cocci (80% due to strep). Methicillin-resistant S. aureus should be covered
2.Deep ulcers with extension to fascia typically include gram negative bacilli (such as P. aeruginosa and Proteus) in addition to GPC
3.Wounds with extensive local inflammation and signs of systemic toxicity should be presumed to have anaerobic organisms in addition to the above pathogens
Remember that DM often have PVD, which reduces wound healing. Check pulses and refer to vascular surgery if there is evidence of PVD
Also, consider abscess and osteomyelitis in this population. They may miss infections due to neuropathy, which allows for infection progression
Of note, agressive surgical intervention of diabetic foot infections DOES reduce above ankle amputuation

#3. Scoring systems for Necrotizing Fasciitis
LRINEC score (see NEJM article) is a commonly cited diagnostic tool for nec fasc
The following labs are used to predict risk:
* Serum C-reactive protein ≥150 mg/L (4 points)
* White blood cell count 15,000 to 25,000/microL (1 point) or >25,000/microL (2 points)
* Hemoglobin 11.0 to 13.5 g/dL (1 point) or ≤11 g/dL (2 points)
* Serum sodium less than 135 meq/L (2 points)
* Serum creatinine greater than 1.6 mg/dL (141 micromol/L) (2 points)
* Serum glucose greater than 180 mg/dL (10 mmol/L) (1 point)

Score ≥6 is suspicious for necrotizing fasciitis and should prompt surgical consult
≥8 is highly predictive (>75 percent)
The score is only useful when severe soft tissue infection is strongly suspected.
Imaging studies should not delay surgical intervention!

References:
Read more: Harrison's Ch. 119
Tan, et al. Clinical ID. Can Aggressive Treatment of Diabetic Foot Infections Reduce the Need for Above-Ankle Amputation?
UpToDate. See table 2 and 3 for treatment recommendations
http://www.uptodate.com/online/content/topic.do?topicKey=skin_inf/13375&selectedTitle=1~150&source=search_result#H15

(Ellen Eaton MD, 3/3/11)