Point-of-care Ultrasound for Diagnosis of Abscess in Skin and Soft Tissue Infections

Traditionally, emergency department (ED) physicians rely on their clinical examination to differentiate between cellulitis and abscess when evaluating skin and soft tissue infections (SSTI). Management of an abscess requires incision and drainage, whereas cellulitis generally requires a course of antibiotics. Misdiagnosis often results in unnecessary invasive procedures, sedations (for incision and drainage in pediatric patients), or a return ED visit for failed antibiotic therapy.

The objective was to describe the operating characteristics of point-of-care ultrasound (POCUS) compared to clinical examination in identifying abscesses in ED patients with SSTI.

We systematically searched Medline, Web of Science, EMBASE, CINAHL, and Cochrane Library databases from inception until May 2015. Trials comparing POCUS with clinical examination to identify abscesses when evaluating SSTI in the ED were included. Trials that included intraoral abscesses or abscess drainage in the operating room were excluded. The presence of an abscess was defined by drainage of pus. The absence of an abscess was defined as no pus drainage upon incision and drainage or resolution of SSTI without pus drainage at follow-up. Quality of trials was assessed using the QUADAS-2 tool. Operating characteristics were reported as sensitivity, specificity, positive likelihood ratio (LR+), and negative likelihood ratio (LR-), with their respective 95% confidence intervals (CI). Summary measures were calculated by generating a hierarchical summary receiver operating characteristic (HSROC) model.

Of 3,203 references identified, six observational studies (four pediatric trials and two adult trials) with a total of 800 patients were included. Two trials compared clinical examination with clinical examination plus POCUS. The other four trials directly compared clinical examination to POCUS. The POCUS HSROC revealed a sensitivity of 97% (95% CI = 94% to 98%), specificity of 83% (95% CI = 75% to 88%), LR+ of 5.5 (95% CI = 3.7 to 8.2), and LR- of 0.04 (95% CI = 0.02 to 0.08).

Existing evidence indicates that POCUS is useful in identifying abscess in ED patients with SSTI. In cases where physical examination is equivocal, POCUS can assist physicians to distinguish abscess from cellulitis.