Imaging Features of Calcium Pyrophosphate Deposition Disease: Consensus Definitions From an International Multidisciplinary Working Group

Abstract

Objective: To develop definitions for imaging features being considered as potential classification criteria for calcium pyrophosphate deposition (CPPD) disease, additional to clinical and laboratory criteria, and to compile example images of CPPD on different imaging modalities.

Methods: The American College of Rheumatology and European Alliance of Associations for Rheumatology CPPD classification criteria Imaging Advisory Group (IAG) and Steering Committee drafted definitions of imaging features that are characteristic of CPPD on conventional radiography (CR), conventional computed tomography (CT), dual-energy CT (DECT), and magnetic resonance imaging (MRI). An anonymous expert survey was undertaken by a 35-member Combined Expert Committee, including all IAG members. The IAG and 5 external musculoskeletal radiologists with expertise in CPPD convened virtually to further refine item definitions and voted on example images illustrating CR, CT, and DECT item definitions, with ≥90% agreement required to deem them acceptable.

Results: The Combined Expert Committee survey indicated consensus on all CR definitions. The IAG and external radiologists reached consensus on CT and DECT item definitions, which specify that calcium pyrophosphate deposits appear less dense than cortical bone. The group developed an MRI definition and acknowledged limitations of this modality for CPPD. Ten example images for CPPD were voted acceptable (4 CR, 4 CT, and 2 DECT), and 3 images of basic calcium phosphate deposition were voted acceptable to serve as contrast against imaging features of CPPD.

Conclusion: An international group of rheumatologists and musculoskeletal radiologists defined imaging features characteristic of CPPD on CR, CT, and DECT and assembled a set of example images as a reference for future clinical research studies.

Figure 1.. Conventional radiographs of the hand and wrist characteristic of CPPD.

(a) Posteroanterior radiograph of the left hand shows linear and punctate calcifications of the triangular fibrocartilage complex (TFCC) (long arrow), radiocarpal joint (short arrow), and 2^nd and 3^rd MCP joint (arrowheads). (b) Posteroanterior radiograph of the left wrist from a different patient demonstrates linear and punctate calcifications of the TFCC (long arrow), radiocarpal joint (short arrow), and inter-carpal joint hyaline cartilage (arrowhead).

Figure 2.. Conventional radiographs of the knee and pelvis characteristic of CPPD.

(a) Anteroposterior radiograph of the right knee shows linear and punctate calcifications of the medial and lateral menisci (arrows) and femoral hyaline cartilage (arrowhead). (b) Anteroposterior radiograph of the pelvis demonstrates linear calcifications of the fibrocartilage and hyaline cartilage of the pubic symphysis (white arrow), bilateral sacroiliac joints (yellow arrows), right and left hip hyaline cartilage (arrowheads), and left hip labral fibrocartilage (arrowheads). Large cloud-like calcification adjacent to the left ischial tuberosity may represent basic calcium phosphate deposition in the left ilio-psoas bursa or tendon; further imaging was not obtained.

Figure 3.. Conventional unenhanced CT images of the knee and wrist characteristic of CPPD.

(a) Coronal reformatted CT images of bilateral knees show linear calcifications in the right knee hyaline cartilage (long arrows) and punctate calcifications in the left knee menisci (arrowheads). (b) Coronal reformatted CT image of the right wrist from a different patient shows linear and punctate calcifications, less dense than cortical bone located within the TFCC (long arrow) and the scapholunate ligament (arrowhead).

Figure 4.. Conventional unenhanced CT images of the cervical spine in a patient with crowned dens syndrome.

(a) Axial CT image at the level of the odontoid process shows linear calcifications involving the transverse and alar ligaments (arrows). (b) Coronal reformatted CT image of the cervical spine demonstrates punctate calcifications and pannus adjacent to the tip of the dens (arrows).

Figure 5.. Dual-energy CT images of the knee and wrist characteristic of CPPD.

(a) Coronal reformatted DECT image of the right knee shows linear calcifications of the menisci and hyaline cartilage. Color-code represents Z_eff values. The region of interest in the calcification (arrow) has a DEI of 0.028, within the expected range for CPP crystal deposition . DECT was performed using a single-source CT system (Somatom Definition Edge; Siemens Healthineers, Erlangen, Germany). DECT measurements are made with syngo.via VB10B software, “Rho/Z” mode. (b) DECT scan of the left wrist with axial, sagittal, and coronal reformats. Color-code represents Z_eff values. Punctuate calcifications (arrows) are visible in the extrinsic ligaments, on the palmar aspect of the scaphoid and lunate bones. Calcifications have a DEI of 0.027, within the expected range of CPP crystal deposition . DECT was performed using a single-source CT system (Somatom Definition Edge; Siemens Healthineers, Erlangen, Germany). DECT measurements are made with syngo.via VB10B software, “Rho/Z” mode.