Surface skin temperature measured via thermal imaging alone or in combination with the ALT-70 prediction model may decrease the overdiagnosis of cellulitis.
Cellulitis is misdiagnosed in up to 30% of cases due to mimicker conditions known as pseudocellulitis, and this results in an overuse of antibiotics.
In the prospective diagnostic validation study of patients who presented to the emergency department with acute dermatologic lower extremity symptoms, researchers noted statistically significant differences in all skin surface temperature measures (mean, maximum, and gradients) between patients with cellulitis and patients with pseudocellulitis.
Skin surface temperature and the ALT-70 (asymmetry, leukocytosis, tachycardia, and age ≥70 years) prediction model score individually demonstrated high sensitivity (93.5% and 98.8%, respectively), but specificity was optimized by combining the two measures (53.9%), the study found.
Researchers obtained temperature measures for affected and unaffected skin. Cellulitis versus pseudocellulitis was assessed by a six-physician, independent consensus review. Differences in temperature measures were compared using the t-test. Logistic regression was used to identify the temperature measure and associated cut point with the optimal performance for discriminating between cellulitis and pseudocellulitis. Diagnostic performance characteristics for the ALT-70 prediction model, surface skin temperature, and both combined were also assessed.
Of 204 participants who had a consensus diagnosis of cellulitis, there were statistically significant differences in all skin surface temperature measures (mean temperature, maximum temperature, and gradients) between cellulitis and pseudocellulitis. The maximum temperature of the affected limb for patients with cellulitis was 33.2 °C compared with 31.2 °C for those with pseudocellulitis. The maximum temperature was the optimal temperature measure with a cut point of 31.2 °C in the affected skin. The sensitivity of all 3 measures remained above 90%, while specificity varied considerably (ALT-70, 22.0%; the maximum temperature of the affected limb, 38.4%; combination measure, 53.9%, the researchers report.
“As most misdiagnosis cases involve inappropriately classifying noncellulitis as cellulitis, it is important for diagnostic tools to not only identify true negatives but also minimize false-positive results that can perpetuate unnecessary admissions and antibiotic prescribing,” conclude researchers who were led by an emergency medicine physician at the University of Wisconsin–Madison School of Medicine and Public Health in Madison, WI. ” Our data indicate that thermal imaging and ALT-70 are best viewed as complementary tools, which may have distinct applications based on setting and clinical scenario.”
The study is published in JAMA Dermatology.
In an editorial accompanying the new study, Boston dermatologists David G. Li, MD, MBA, and Arash Mostaghimi, MD, MPH, write that the new research “reflects the latest step in a quest for improved diagnosis and treatment of cellulitis and reflects both the opportunity and the challenge for clinicians moving forward.”
Both the ALT-70 prediction model and thermal imaging have low specificity, they note. “Therefore, combining the two modalities may be helpful to reduce the likelihood of this occurring,” they wrote. “This combination may be especially beneficial in settings where the pretest probability of cellulitis is low, in which case a dermatology consultation may also be helpful. “
The ALT-70 prediction model alone demonstrated a negative predictive value of 95.2%, which confirms its potential as a screening test to rule out cellulitis.
The bottom line? These findings “underscore the importance of these point-of-care modalities to enhance patient care for presumed cellulitis.”
