POS1150 ANATOMICAL LOCATIONS AND CORRELATES OF CALCIUM PYROPHOSPHATE CRYSTAL DEPOSITS OF THE SPINE – PATHOLOGIC EXAMINATION OF 77 SURGICAL CASES
Authors: J. Dau, G. Ho, H. Choi, J. Schwab, M. Kohler
Journal: Annals of the Rheumatic Diseases (2021)

Background: Spinal involvement in calcium pyrophosphate deposition disease (CPPD) is thought to be a rare occurrence and is seen infrequently as crowned dens syndrome. Furthermore, data on anatomical locations and correlates of calcium pyrophosphate (CPP) deposits in spinal CPPD are scarce. Objectives: To describe the anatomical locations and correlates of pathologically confirmed CPPD of the spine. Methods: Consecutive patients with spinal CPPD were identified via retrospective chart review of individuals who underwent spine surgery for intractable chronic neck or back pain at Massachusetts General Hospital between 2009 and 2014. These deposits and surrounding anatomical structures were surgically resected and confirmed to have calcium pyrophosphate deposition upon pathologic review. We reviewed musculoskeletal imaging (CT, MRI, XR) and laboratory data from these pathologically confirmed cases. Results: From April 2009 to August 2014, we identified 77 individuals with pathologically confirmed CPPD of the spine. The mean age was 68 years; 41 (53%) were female; mean BMI was 28.7. Calcium pyrophosphate (CPP) was grossly identified intraoperatively by the surgeon in 38 cases (50%), typically as “chalky white deposits” (Figure 1). CPP deposits were seen most frequently in the ligamentum flavum (23%) and intervertebral disc (23%), followed by other less common locations (Table 1). Imaging findings in the soft tissue or intervertebral disc suggestive of CPPD were found in 5 cases (6%), whereas findings of spinal canal narrowing, facet arthropathy, or ligamentum flavum thickening were eventually correlative with CPP deposits in pathologic specimens. Only 7 (9%) experienced a prior episode of acute CPP arthritis (pseudogout). Chondrocalcinosis on x-ray was seen in 26 cases (34%), most commonly in the wrist and/or knees. Osteoarthritis was present in all spinal imaging, and 65% had comorbid scoliosis. Laboratory abnormalities associated with secondary causes of CPPD (hypercalcemia, hypomagnesemia, hyperparathyroidism) were not seen with spinal CPPD. Conclusion: Spinal CPPD may occur more frequently than previously perceived. The ligamentum flavum and intervertebral discs were common anatomical locations for spinal CPPD. Advanced imaging of the spine showed low sensitivity for detecting spinal CPPD. Only a small minority had typical peripheral joint involvement or imaging with peripheral joint chondrocalcinosis. Thus, without pathologic confirmation, the vast majority of cases would remain unidentified. These findings call for the need to seek pathologic confirmation to determine the robust epidemiology and also raise the potential role for preoperative CPPD treatment. Table 1. Spinal Anatomic Locations of Pathologically Confirmed CPPD Spinal Anatomic Location No. of Sites (%)* ligamentum flavum 29 (23) Intervetebral Disc 28 (23) Other Location 19 (15) Posterior Elements 18 (15) Facet 14 (11) Synovium 8 (6) Interspinous Ligament 3 (2) Subarticular/Lateral Recess 2 (2) Fibrocartilaginous Tissue 1 (1) Inner Spine 1 (1) Other Ligament 1 (1) * Some patients had more than one anatomic location where CPP was isolated Figure 1. Gross visualization of calcium pyrophosphate deposition (black arrow) Disclosure of Interests: Jonathan Dau: None declared, Gary Ho: None declared, Hyon Choi Consultant of: Ironwood, Selecta, Horizon, Takeda, Kowa, Vaxart, Grant/research support from: Ironwood, Horizon, Joseph Schwab: None declared, Minna Kohler Speakers bureau: Eli Lily, Consultant of: Novartis.