Pearls for lower-extremity cellulitis

Cellulitis does not have a gold standard for a diagnostic test and is a clinical diagnosis. It's frequently misdiagnosed, a fact confirmed by two recent meta-analyses and reviews. The first, published Oct. 3, 2022, in the Journal of Hospital Medicine, looked primarily at inpatients and found that 39% of cellulitis diagnoses were incorrect. The most common final diagnosis when cellulitis was misdiagnosed was venous stasis, at 18%. The most common infectious alternative diagnosis was abscess, at 10%.

The second review, published May 25, 2023, in the Journal of General Internal Medicine, included more studies from an outpatient setting and found a range of misdiagnoses from 19% to 83%, with a mean of 41%. The most common alternative diagnoses were stasis dermatitis, eczematous dermatitis, and edema/lymphedema.

Many years ago, a podiatrist taught me to lift the leg with suspected infection to see if the erythema drained away. If it did, the erythema was not due to cellulitis. I can't remember a time this pearl has failed me. This is derived from a key article by Jan Hirschmann, MD, and Gregory Raugi, MD, of Seattle, which appeared in the August 2012 Journal of the American Academy of Dermatology.

Lifting a leg to see if the erythema drains was first described by Leo Buerger, MD, but it was a test for peripheral arterial disease, not cellulitis. Called Buerger's test, it looked at dependent rubor and was called erythromelalgia or erythromelia. But those terms now refer to a specific, rare disorder. Dependent rubor appears to be caused by dilated superficial capillaries.

Buerger's test may be highly sensitive for severe arterial disease below the popliteal fossa, but the specificity is low. I believe patients with erythema due to venous stasis dermatitis or edema also exhibit an improvement in redness when the leg is elevated above the level of the heart. For the purpose of reducing our misdiagnoses of cellulitis, it may not matter what the cause of the dependent rubor is as long as dependent rubor tells us the erythema is unlikely to be from cellulitis.

Caveats to be aware of include that a lack of dependent rubor does not rule in cellulitis. Erythema that doesn't drain could be due to contact dermatitis, eczema, or other disorders. Sometimes there will be edema and inflammation surrounding an infection that will drain with elevation, but the infected area will remain erythematous. This can happen with an abscess.

ALT 70 is a clinical prediction model that has been validated in the ED but not in outpatient settings. Other models have not been validated. Adding a test for dependent rubor to the clinical prediction models may improve diagnostic accuracy and avoid unnecessary antibiotics and hospitalizations.

Once the diagnosis of cellulitis is made, an addition of ibuprofen or a steroid might improve outcomes. Most cellulitis is caused by streptococci, which release toxins once appropriate antibiotics are started, so it's possible giving ibuprofen or a steroid prior to antibiotics would improve outcomes versus giving antibiotics first. A small unblinded trial found an 80% improvement in inflammation at 48 hours in patients getting ibuprofen versus 10% in patients who didn't get ibuprofen. A randomized controlled trial for ibuprofen that appeared March 5, 2017, in Clinical Microbiology and Infection was negative but it was powered to find a very large difference. The researchers did find a 15% improvement in "proportion of patients with regression of inflammation within 48 hours."

Prednisolone has been shown to help time to improvement in erysipelas. In one study, published in 1997 in the Scandinavian Journal of Infectious Diseases, the authors defined erysipelas as an "acute, superficial cellulitis that also involves the lymphatic capillaries." Patients were randomized to an eight-day prednisolone taper or placebo. All patients got antibiotics. The prednisolone was given soon after admission at 30 mg for the first two days, 15 mg for the next two days, 10 mg for the next two days, and 5 mg a day for the last two days. The primary outcome was time to healing, which was five days in the steroid group and six days in the placebo group. For secondary outcomes, the group getting steroids had one less day on IV antibiotics and one less day of hospital admission.

In a one-year follow-up study in 1998 in the same journal, there were fewer relapses of cellulitis in the steroid group, though the finding was not statistically significant.

Just remember, not everything that's red is an infection. With cellulitis, like other infections, you really probably should order a white count, the patient should feel ill, and the area of suspected infection should hurt.