Background The diagnosis of calcium pyrophosphate deposition disease (CPPD) by detection of calcium pyrophosphate crystals in the synovial fluid may be difficult or impossible for technical reasons. Currently, conventional X-rays are used with a high specificity but a low sensitivity.
Objectives The aim of this study is to assess ultrasonography efficiency in the diagnosis of CPPD. The secondary objectives are to determine an ultrasound sensitive site for the diagnosis and to compare ultrasonography to conventional radiography.
Methods We conducted a bicentrique transversal prospective study. Every patient with knee arthritis was included and had an arthrocentesis, conventional radiography of the knee and an ultrasound of the knee (meniscus, capitellum and trochlea) and the wrists. The ultrasound examiner was blinded of the fluid histologic findings. The final diagnosis was performed by the synovial fluid analysis which was made by various examiners. Ultrasound diagnosis of CPPD was established if there were at least one typical calcification found during the examination (hyperechoic bands parallel to the surface of the hyaline cartilage and “punctate” pattern composed of several thin hyper-echoic spots).
Results 78 patients were included: 22 CPPD, 11 gouts (with no chalky gout), 16 inflammatory rheumatisms, 14 osteoarthritides and 15 undetermined arthritides. 20 patients had radiographic signs of CPPD and 39 patients had ultrasound signs (21 CPPD, 5 gouts, 4 inflammatory rheumatisms and 5 osteoarthritides). In our study ultrasound has a sensitivity of 95,4%, a specificity of 65,8%, a positive predictive value of 60% and a negative predictive value of 96,4% in the diagnosis of CPPD. Radiography of the knee has a sensitivity of 77.7%, a specificity of 92,7%, a positive predictive value of 85% and a negative predictive value of 88,8%. There was no statistical difference between ultrasound and conventional radiography regarding the sensitivity (p=0,219). The meniscus analysis in ultrasound is statistically the most sensitive site for the detection of CPPD (p=0,006).
Conclusions Regarding the sensitivity of ultrasound for the CPPD's diagnosis, our results are in agreement with the literature (1,2) in contrast to our specificity which could be related to the heterogeneity of the assessers (real-life study). Ultrasound is an examination at least as efficient as conventional radiography in the diagnosis of CPPD, however it presents the benefits of being easier to carry out by the rheumatologists, cheaper and less irradiate.
Filippou G, Frediani B, Gallo A, et al. A “new” technique for the diagnosis of chondrocalcinosis of the knee: sensitivity and specificity of high-frequency ultrasonography. Ann Rheum Dis 2007;66:1126-28
Gutierrez M, Di Geso L, Salaffi F, et al. Ultrasound detection of cartilage calcification at knee level in calcium pyrophosphate deposition disease. Arthritis Care and Research. 2014; 66:69-73
Disclosure of Interest None declared