Point-of-care ultrasound algorithm offers 'rule-in diagnostic tool' for transient synovitis
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In children who present to the pediatric ED, a point-of-care ultrasonography decision-support algorithm — a rule-in tool — accurately diagnosed transient synovitis, according to data published in JAMA Network Open.
“Transient synovitis (TS) is a self-limiting disease characterized clinically by acute hip pain,” Marah Zoabi, BSc, of the Technion-Israel Institute of Technology, in Haifa, and colleagues wrote in a research letter. “The diagnosis is confirmed by excluding other severe diseases, such as septic arthritis, osteomyelitis and Legg-Calvé-Perthes disease. Ultrasonography examination frequently reveals hip effusion.”
“A point-of-care ultrasonography (POCUS) decision-support algorithm (DSA) is regularly used to identify TS in the pediatric ED of Rambam Health Care Campus, a tertiary hospital in Haifa, Israel,” they added. “The POCUS-DSA includes a set of 5 clinical criteria that must be met, followed by bedside ultrasonography examination of the hip joint.”
To assess the POCUS-DSA’s performance in diagnosing transient synovitis in children in a pediatric ED, Zoabi and colleagues conducted a retrospective analysis of all pediatric patients with nontraumatic hip tenderness who met the POCUS-DSA criteria at the Rambam Health Care Campus between Jan. 1, 2014, and Dec. 31, 2019. In all, the researchers examined data from 1,461 children during the study period.
Those with hip effusion received a diagnosis of transient synovitis in the ED and were scheduled for a follow-up visit in 5 to 7 days. Meanwhile, those without hip effusion were assessed with laboratory or imaging tests based on clinician determination. A final diagnosis of transient synovitis was made for any patient who demonstrated spontaneous resolution of symptoms and a reduction in effusion at follow-up.
In all, POCUS-DSA was applied to 621 patients with a mean age of 5.5 years.
The researchers used sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), positive likelihood ratio (LR) and negative LR to assess the accuracy of POCUS-DSA.
According to the researchers, 539 patients were correctly diagnosed as having transient synovitis in the ED, while 22 were correctly diagnosed as not having the disease. Meanwhile, 54 were misdiagnosed as not having transient synovitis but later correctly diagnosed during follow-up visits. Six ED patients were misdiagnosed as having the disease but were found to have another condition at follow-up visits. All these patients recovered completely.
In diagnosing transient synovitis, POCUS-DSA demonstrated a sensitivity of 90.9% (95% CI, 88.3% to 93.1%), a specificity of 78.6% (95% CI, 60.5% to 89.8%), a PPV of 98.9% (95% CI, 97.6% to 99.5%), an NPV of 28.9% (95% CI, 20% to 40%), a positive LR of 4.25 (95% CI, 2.1-8.6), and a negative LR of 0.12 (95% CI, 0.08-0.16). In all, 7.8% of those without hip effusion underwent blood tests.
“To our knowledge, this study is the first to suggest a rule-in diagnostic tool for TS, instead of one of exclusion,” Zoabi and colleagues wrote. “The traditional approach advocates the use of laboratory tests to differentiate between TS and other serious diseases. In our cohort, only 7.8% of the children underwent blood tests. Avoiding unnecessary blood tests by using the POCUS-DSA can reduce the number of children who undergo venipuncture and minimize pain and distress.”
Perspective
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N. Lawrence Edwards, MD
Point-of-care ultrasound (POCUS) is gradually becoming a fixture in rheumatologists’ offices around the United States, with most rheumatology fellowships offering this training either as an internal emersion or through web-based programs. A new generation of trainees view this technology as an enhancement to their physical diagnostic skills. I have even heard our own fellows refer to POCUS as “the rheumatologist’s stethoscope.”
Enthusiasm for being able to identify the detailed architecture of diarthrodial joints and the surrounding soft tissues is an excellent reminder that anatomy is at the very core of our specialty. This enthusiasm, however, should be tempered by the lack of sensitivity and specificity of many ultrasound findings.
The research letter by Zoabi and colleagues from Haifa points out the need for a decision-support algorithm for various rheumatic conditions when viewing ultrasound images. Algorithms that help define the clinical settings in which POCUS findings have the most meaning will certainly add to the validity of POCUS as a diagnostic tool.
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