Articular and periarticular spinal calcifications in relation to synovial fluid findings in patients with calcium pyrophosphate dihydrate deposition disease (CPPD)

Abstract Background Calcium pyrophosphate dihydrate deposition disease (CPPD) is the second most common form of the crystal-associated arthritis. Diagnosis is achieved by detection of crystals by polarized light microscopy and/or detection of hyaline cartilage or fibrocartilage calcifications characteristic of CPPD deposition by musculoskeletal ultrasound (MSUS). Axial involvement with intervertebral disc calcification, sacroiliac erosions, and sub-chondral cysts of the facet joints occurs with CPPD deposition. Aim To assess the presence and relation between calcification of intervertebral discs, other articular and periarticular spinal structures, and synovial fluid analysis (SFA) and MSUS calcifications in patients with CPPD deposition disease. Methods One hundred patients with CPPD disease diagnosed according to the modified proposed diagnostic criteria by McCarty 1994 were included. Plain radiography on the spines, pelvis, and affected joints, MSUS on affected joints, and synovial fluid analysis (SFA) were done. Results Spinal calcification was present in 55% of patients. The commonest site was anterior longitudinal ligament (43%). Characteristic CPPD calcifications by plain radiography on the knee and wrist joints were present in 38% and 16% respectively. Characteristic CPPD calcifications by MSUS on the knee and wrist joints presented in 93% and 27% respectively. CPPD crystal detection by SFA was 97%. The accuracy of MSUS to diagnose CPPD deposition disease is more than double that of plain radiography, and it is comparable to that of synovial fluid analysis. The result of intra-rater analysis between SFA by polarized light microscopy and MSUS was kappa 0.767 (p < 0.001); this indicates substantial level of agreement between SFA and MSUS; between plain radiography and MSUS, it was kappa 0.188 (p = 0.32) which indicates slight agreement, and between plain radiography and SFA, it was kappa 0.037 (p = 0.1) which fails to reach a significant level of agreement. There was a significant positive relation between spinal calcification and wrist joint calcification by plain radiography. Conclusion Considerable spinal affection by CPPD deposition disease can be detected. Although the most definitive, reliable direct approach for CPPD deposition disease diagnosis is SFA using polarized light microscopy, MSUS is considered a useful non-invasive diagnostic tool in this situation. In CPPD deposition disease, MSUS has proven to be an excellent technique for detecting calcification in the articular tissue disease compared to conventional radiography