Using criteria outlined by the Outcome Measures in Rheumatology (OMERACT) international panel, investigators found ultrasound to be a reliable diagnostic tool for identifying calcium pyrophosphate deposition disease (CPPD), particularly in the triangular fibrocartilage of the wrist (TFC) and the acromioclavicular (AC) joints. The study was published in the Annals of the Rheumatic Diseases.
Although CPPD is a common arthropathy in the elderly, the prevalence remains uncertain due to an invasive diagnostic gold standard of synovial fluid analysis that is not always performed when indicated, coupled with the low sensitivity of X-rays, which leads to probable underdiagnosis. Ultrasound is a safe and noninvasive alternative that the researchers hoped would prove reliable for the detection of CPPD.
A panel of 30 OMERACT members was initially gathered for a web-based exercise. The experts assessed images from the TFCs, AC, metacarpal-phalangeal, and hip joints, rating each for the presence or absence of CPPD. After the exercise, 19 of these experts participated in a patient-based exercise, in which they rated 8 patients’ images for the presence or absence of CPPD. In both exercises, all readers assessed the images twice, to allow for intra-observer and inter-observer reliability calculations.
The web-based exercise revealed high measurements of inter-observer reliability, with an overall mean agreement level of 0.83 and a mean kappa value of 0.66 across all sites. The TFC and AC joint each demonstrated agreement levels of 0.87 and kappa values of 0.75. Intra-observer reliability
values were also high, with a mean agreement of 0.91 and a kappa of 0.81 across all sites. The TFC and AC joints also yielded mean agreement values of 0.92 and 0.93 and mean kappa values of 0.82 and 0.85, respectively.
In the patient exercise, inter-observer reliability, which ranged from poor to excellent depending on site, had an overall mean level of agreement of 0.71 and a mean adjusted kappa of 0.42 across all sites. The mean agreement levels were highest for the TFC and AC joints, registering estimates of 0.91 and 0.75, respectively. In addition, the kappa values for the TFC and AC joints were 0.82 and 0.51, respectively. Intra-observer reliability saw overall means of 0.85 on agreement level, and 0.71 for kappa value; these estimates were also high for the TFC and AC joints, with agreement levels of 0.93 and 0.88 and kappa values of 0.87 and 0.76, respectively.
As a secondary objective, researchers also compiled a reference atlas of CPPD ultrasound images based on these exercises, depicting a range of presentations from singular crystal deposits to diffuse disease, which could provide clinicians and researchers with a valuable pictorial ultrasound map of CPPD.
The study results support the use of ultrasound for the diagnosis of CPPD, particularly when assessing the TFCs and AC joints. The investigators recommend that the scanning technique be refined to provide even more reliability (possibly at other sites), but suggest that ultrasound should be used for diagnosis and follow-up of patients with CPPD.
The authors acknowledge the contribution of General Electric Healthcare 27 Italy and Samsung Electronics Italia s.p.A for providing ultrasound equipment for this study.
There were no conflicts of interest declared.
Filippou G, Scirè CA, Adinolfi A, et al. Identification of calcium pyrophosphate deposition disease (CPPD) by ultrasound: reliability of the OMERACT definitions in an extended set of joints – an international multiobserver study by the OMERACT Calcium Pyrophosphate Deposition Disease Ultrasound Subtask Force [published online March 13, 2018]. Ann Rheum Dis. doi:10.1136/annrheumdis-2017-212542