Michael Kosofsky, MS4

Article: Subramaniam, et al. “Point-of-care Ultrasound for Diagnosis of Abscess in Skin and Soft Tissue Infections” Academic Emergency Medicine 2016. Vol 23, No 11 (1298-1306)

The Idea: Skin and soft tissue infections include both cellulitis and abscesses of the skin and superficial facial. Over the past two decades, the number of patients evaluates for SSTI has increased dramatically, along with the use of incision and drainage. Historically, both diagnoses were made based on history and physical, although associated with fair to poor inter-rater reliability. Misdiagnosis of cellulitis for abscesses can result in repeat visits when antibiotics fail resolution. Misdiagnosis of the reverse can result in unnecessary I&D. This study compared the use of POCUS in aiding in the diagnosis of cellulitis versus abscess.

The Study: Systematic Review of 6 trials, all prospective, observational studies conducted in the ED from 2005-2015.

Inclusion Criteria: Trials that compared clinical examination and ultrasound detection for detection of abscess in patients of any age were included> Trials were only included if the standard for abscess diagnosis was pus drainage on incision or at follow-up. Lack of abscess was defined as no pus drainage on incision or resolution of SSTI at follow-up

Exclusion Criteria: Trials were excluded if they were not conducted in the ED or by emergency physicians. Trials were also excluded if they included intraoral abscesses or abscesses that required drainage in the operating room.

Initially the systematic review began with 4155 articles, which in the end was narrowed to six trials, which included 800 patients in total. They were prospective observational studies that were conducted in the ED and compared POCUS with clinical examination in diagnosing abscess, with pus drainage as criterion standard when evaluation SSTI. Four trials were on pediatric patients, and two were on adult patients. Two studies had study physicians perform a combined clinical examination and POCUS prior to diagnosis. The remaining trials sought to have study physicians blinded from the clinical examination, by only performing POCUS prior to diagnosis. Two trials had specific operating characteristics of POCUS with or without clinical examination compared to clinical examination alone for a subgroup of clinically nonevident or equivocal SSTI lesions.

Outcome Measured

• Adams et al. Sensitivity and Specificity of clinical evaluation (CE) vs. POCUS for diagnosis

• Marin et al. Sn and Specificity of CE vs. CE plus POCUS for diagnosis

• Berger et al. Sensitivity and specificity of CE vs POCUS for diagnosis

• Iverson et al. Sensitivity and specificity of CE vs. POCUS for diagnosis

• Sivitz et al. Sensitivity and specificity of CE vs. POCUS for diagnosis

• Squire et al. Sensitivity and Specificity of CE vs. CE plus POCUS for diagnosis

Results: The sensitivity of POCUS ranged from 90% to 98% and the specificity ranged from 67% to 88% in the included trials. The sensitivity of clinical examination ranged from 75% to 95% and the specificity ranged from 60% to 84%

Overall pooled sensitivity and specificity for POCUS (using data from all trials except for Marin et al.19) were 97% (95% CI = 94% to 98%) and 83% (95% CI = 75% to 88%) respectively. LR+ was 5.5 (95% CI = 3.7 to 8.2), and LR - was 0.04 (95% CI = 0.02 to 0.08).

Description of POCUS training was outlined in each study, but the background experienced of ultrasonographers was not routinely described. Some studies rated their ultrasoungraphers as novice, whereas other rated theirs as POCUS credentialed physicians.

Takeaway:

Pocus is superior in abscess diagnosis relative to clinical examination alone, in both pediatric and adult populations Both Martin et al and Adams et all performed a subgroup analysis that investigated clinically equivocal lesions, and found POCUS to be far superior to CE alone.

POCUS is important in pediatric populations as correct diagnosis can limit the need to do invasive I&D’s on children that may require procedural sedation. Other imaging modalities have been studied for diagnosis of SSTI. POCUS has been observed to be more sensitive, yet less specific in identifying SSTI in one study of 65 patients. Also it is important to note that MRI remains the superior imaging modality for skin infections like necrotizing faciatisis, as the air created can obscure the ultrasound image.

Limitations:

• Lesion diagnosed as cellulitis at one point in time has the potential to evolve into an abscess hours or days later

• POCUS is able to visualize collections less than 1 cm in volume. Although these lesions can be drained, some physicians may consider them small enough to be suitable for medical management without drainage