Literature Summaries - In Patients Presenting To The Emergency Department With Skin And Soft Tissue Infections; What Is The Diagnostic Accuracy Of Point-Of-Care Ultrasonography For The Diagnosis Of Abscess Compared To The Current Standard Of Care? A Systematic Review And Meta-Analysis
Date: 20 February 2017
Skin and soft tissue infections (SSTIs) are common presentations in ED. According to the different management strategies, emergency physicians must consider the two most common entities in differential diagnosis: abscess and cellulitis. Although an abscess can be diagnosed with only inspection and palpation, sometimes it can be difficult to achieve a true diagnosis because these two can be associated with each other to varying degrees. This can be misleading, particularly in the pediatric population, for which physical examination usually is not reliable. Since cellulitis is treated with systemic antibiotic therapy and an abscess is treated using the “abscess is equal to drainage” motto, it is important to make an accurate differential diagnosis in order to decrease unintentional surgical interventions and, thus, malpractice lawsuits.
- The primary aim of this study was to determine the accuracy of point-of-care ultrasonography (POCUS) in diagnosing an abscess in ED patients with SSTIs.
- The secondary objective was the accuracy of POCUS in the pediatric population subgroup.
For this purpose, prospective studies conducted in both adult and pediatric emergency departments were systematically reviewed. With a little detail, the authors systematically evaluated prospective cohort and case control studies investigating SSTIs (abscess or cellulitis) with a definitive POCUS protocol between 1946 and 2015 in the following databases: PubMed, EMBASE, MEDLINE, and Cochrane Systematical Database. As an index test, utilization of POCUS in diagnosing abscesses in patients presenting to emergency departments with SSTI findings was investigated. The authors used a combined standard reference of (1) purulent discharge from an incision and drainage, (2) abscess or cellulitis on CT results according to radiologist’s opinion, or (3) a final diagnosis from a clinical follow-up. No restriction was made on the protocol of ultrasonography used to diagnose an abscess, and no restriction on the type of emergency physician was made. Case reports, retrospective studies, and other types of case-control studies were excluded.
The review was carried out according to the Cochrane Handbook and PRISMA guidelines. The methodological quality of each selected article was assessed by two independent authors according to QUADAS-2 criteria. A subgroup of pediatric cases was formed. In this subgroup, the effects and the differences of the management of SSTIs in the pediatric population were investigated post hoc.
Here, we would like to give some information about QUADAS criteria. These criteria act as a test used in reviews of primary diagnostic accuracy studies to evaluate the applicability of the index test and the risk of bias. In 2003, QUADAS was formed through the collaboration of York and Amsterdam universities and was used first by the Cochrane Collaboration in systematical reviews. Eventually, it was recommended by NICE and AHRQ as well. In 2010, these criteria were revised and updated as the QUADAS-2 criteria.
The QUADAS-2 assesses four potential areas for bias and applicability to the research question:
- patient selection—the risk of bias was high if the study was a case-control design, enrollment was nonconsecutive, or the study had inappropriate exclusions;
- index test—if the results from the incision and draining were incorporated into the U.S. results, the risk of bias was high;
- references standard—the risk of bias was high if the reference standard could misclassify the target condition or the reference standard was interpreted with knowledge of the POCUS results; and
- flow and timing—the risk of bias was high if not all patients received the same POCUS protocol (index test), not all patients received the same reference standard, or not all patients were included in the analysis.
Among 3028 studies, eight studies correlated moderate to high when QUADAS-2 criteria were selected. There were three studies (1) (2) (3) in adult settings and, five studies (4) (5) (6) (7) (8) in pediatric settings with a sample size of 747 patients. All studies except one (4) were conducted in the United States. Analysis of the data-extraction process by two independent reviewers revealed a κ value of 0.80, representing a significant correlation between two independent reviewers.
The authors determined that the sensitivity of POCUS in the eight included studies ranged from 65.0% to 100% and the specificity from 30.0% to 100%. Combined test characteristics revealed that, for patients presenting to an emergency department with SSTI findings, POCUS had a sensitivity of 96.2% (95% CI, 91.1–98.4%), a specificity of 82.9% (95% CI, 60.4–93.9%), a positive LR of 5.63 (95% CI, 2.2–14.6), and a negative LR of 0.05 (95% CI, 0.01–0.11) in diagnosing abscess.
In the pediatric subgroup, combined test characteristics were as follows: a sensitivity of 93.9% (95% CI, 84.8–97.7%), a specificity of 82.9% (95% CI, 34.2–97.9%), a positive LR of 5.5 (95% CI, 0.9–33.9), and a negative LR of 0.07 (95% CI, 0.03–0.15). There has been a change in the management of treatment strategy of 14% to 27%. The proportion of patients who initially were determined to need drainage based on clinical examination and who subsequently ended up not receiving drainage based on POCUS findings ranged from 12% to 20%. The proportion of patients who ended up receiving drainage based on POCUS findings after initially being determined not to require drainage ranged from 13% to 18%.
These rates were even slightly higher in the adult age group. The proportion of patients who received unplanned drainage after POCUS ranged from 23% to 40%. After POCUS, there was a change in management in the adult population ranging 17% to 56%, meaning almost half of the patients. Thus, the authors suggested that clinical examination was neither sensitive nor specific in diagnosing an abscess. They also added that POCUS is superior to clinical examination in diagnosing abscess in both pediatric and adult populations.
The strengths of this study are a strict adherence to a systematic review methodology and the use of standardized and validated data collection and extraction tools that limit bias and increase inter-rater reliability. The subgroup analysis of the diagnostic accuracy in pediatric patients, who may not tolerate physical examination, blood testing, and needle aspiration as readily as adults, is also a positive aspect of this study. However, this very strict adherence to systematic methodology led to a relatively small amount of the sampling population (747) since only eight of 3028 studies were included in the review. This situation raises concerns of a bias risk. Also, only one study (4) shares data about sensitivity and specificity. As stated by the authors, in some patients, SSTIs can start as cellulitis and complicate into abscess. Due to this, it is crucial to acknowledge the time of the presentation of the patients to ED for accuracy of the results in studies included in this review.
1. ABSCESS: applied bedside sonography for convenient evaluation of superficial soft tissue infections. Squire BT, Fox JC, Anderson C. Acad Emerg Med, 2005, Cilt 12, s. 601-6.
2. The effect of soft-tissue ultrasound on the management of cellulitis in the emergency department. Tayal VS, Hasan N, Norton JH et al. Acad Emerg Med, 2006, Cilt 13, s. 384-8.
3. Bedside ultrasound performed by novices for the detection of abscess in ED patients with soft tissue infections. Berger T, Garrido F, Green J et al. Am J Emerg Med, 2012, Cilt 30, s. 1569-1573.
4. Ultrasonography in the evaluation of neck abscesses in children. Quraishi MS, O'Halpin DR, Blavney AW. Clin Otolaryngol, 1997, Cilt 22, s. 30-3.
5. Effect of bedside ultrasound on management of paediatric soft tissue infection. Sivitz AB, Lam SHF, Ramirez-Schrempp D et al. J Emerg Med, 2010, Cilt 39, s. 637-643.
6. The effect of bedside ultrasound on diagnosis and management of soft tissue infections in a paediatric ED. Iverson K, Haritos D, Thomas R et al. Am J Emerg Med, 2012, Cilt 30, s. 1347-1351.
7. Emergency ultrasound-assisted examination of skin and soft tissue infections in the paediatric emergency department. Marin JR, Dean AJ, Bilker WB et al. Acad Emerg Med, 2013, Cilt 20, s. 545-553.
8. Point-of-care ultrasonography for the diagnosis of paediatric soft tissue infeciton. Adams CM, Neuman MI, Levy JA. J Pediatr, 2016, Cilt 169, s. 122-7.
Emre Özlüer, Asst. Prof.
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