Multifocal calcific periarthritis with distinctive clinical and radiological features in patients with CD73 deficiency

Objectives: Arterial calcification due to deficiency of CD73 (ACDC) is a hereditary autosomal recessive ectopic mineralization syndrome caused by loss-of-function mutations in the ecto-5′-nucleotidase gene. Periarticular calcification has been reported but the clinical characterization of arthritis as well as the microstructure and chemical composition of periarticular calcifications and SF crystals has not been systematically investigated. Methods: Eight ACDC patients underwent extensive rheumatological and radiological evaluation over a period of 11 years. Periarticular and synovial biopsies were obtained from four patients. Characterization of crystal composition was evaluated by compensated polarized light microscopy, Alizarin Red staining for synovial fluid along with X-ray diffraction and X-ray micro tomosynthesis scanner for periarticular calcification. Results: Arthritis in ACDC patients has a clinical presentation of mixed erosive-degenerative joint changes with a median onset of articular symptoms at 17 years of age and progresses over time to the development of fixed deformities and functional limitations of small peripheral joints with, eventually, larger joint and distinct axial involvement later in life. We have identified calcium pyrophosphate and calcium hydroxyapatite (CHA) crystals in SF specimens and determined that CHA crystals are the principal component of periarticular calcifications. Conclusion: This is the largest study in ACDC patients to describe erosive peripheral arthropathy and axial enthesopathic calcifications over a period of 11 years and the first to identify the composition of periarticular calcifications and SF crystals. ACDC should be considered among the genetic causes of early-onset OA, as musculoskeletal disease signs may often precede vascular symptoms.