Just Because It’s Red Doesn’t Mean It’s Infected!

Cellulitis is a bacterial infection of the skin frequently encountered in patients seen in a wound center. Erysipelas, although slightly different, is a similar skin infection,¹ but for the most part is considered to be a type of cellulitis with similar etiologies and similar treatments. These diagnoses accounted for about 10% of hospital admissions related to infection from 1998 to 2006.² The cost to treat cellulitis in the United States in 2006 was about $3.7 billion.³ A recent report in the literature suggests that our ability to correctly diagnosis cellulitis is greatly overestimated.⁴ The study showed that in a large Boston hospital from June 2010 to December 2012, 259 patients were admitted with a diagnosis of lower extremity cellulitis. By the time of discharge, 30.5% of patients were found to have been misdiagnosed as having cellulitis. Of the group who were misdiagnosed, 84.6% were found to have not needed hospitalization at all and 92.3% received unnecessary antibiotics.⁴ In addition to the huge financial waste, the potential for causing harm with unnecessary antibiotics — mostly intravenously administered — existed. Complications associated with providing intravenous access either peripherally or centrally can be significant. The antibiotic therapy itself can also cause problems such as anaphylaxis or other reactions and Clostridium difficile colitis. 

What, if anything, can we do to minimize the misdiagnosis of cellulitis? Unfortunately, not a lot of help is available. The clinical presentation of these patients usually involves a warm, painful, red, swollen extremity.⁵ One positive finding with cellulitis is that it is usually unilateral. Occasionally, the patients will have a history of a comorbidity such as diabetes mellitus. The risk factor most commonly associated with cellulitis is edema or lymphedema.⁵ This is because lymphatic fluid with its elevated protein content facilitates bacterial growth.⁵ There are numerous laboratory tests that are routinely done in patients suspected of having cellulitis but none, including blood cultures, are considered specific to cellulitis. Cultures of the leg either with the swab technique, needle aspiration of fluid from the subcutaneous tissues, or even biopsy of the tissue are not recommended because the yield is so low.¹ In addition, imaging studies are not helpful to diagnosis cellulitis but may help rule out an abscess or necrotizing fasciitis.⁵  

If it isn’t cellulitis, then what could it be? One of the most common problems we see mimicking cellulitis is dependent rubor, which is seen in patients with peripheral neuropathy and ischemic vascular disease. When the extremity is dependent, the microcirculation is disordered, resulting in a red discoloration. Depending on the severity of the condition, the redness can extend from the toes to the knee. Many times this redness is bilateral. Simply elevating the leg can make the diagnosis; if the redness is the result of neuropathy or ischemia, it will resolve, whereas the redness due to cellulitis will not. Venous stasis dermatitis is commonly mistaken for cellulitis.⁶ Other lower extremity inflammatory conditions such as an acute Charcot joint, gout, and other dermatologic conditions can be mistaken for cellulitis.^4,5

If an infectious etiology is confirmed, antibiotics are definitely indicated, but there is little consensus on the appropriate antibiotic regimen.^5,7 It is felt that treatment of the edema and lymphedema fluid in the leg with compression therapy will make any antibiotic regimen more effective and speed the resolution of the infection and inflammatory reaction.⁸ Another common conclusion is that most of these patients with suspected cellulitis could be treated without hospitalization even if the patient does have cellulitis; unless the patient is septic or significantly immunocompromised, outpatient treatment is being recommended.^9,10

With all this information in mind, it’s time we rethink our approach to the red leg. It’s obvious that all red legs are not infected and that careful evaluation and treatment of these patients are needed to provide not only the appropriate therapy but also safe, cost-effective therapy.