Distribution of calcium pyrophosphate crystal deposits on whole-body low-dose CT scan

 

Bùi Hoàng Anh, Alan Gauffenic, Augustin Latourte, Marina Assadourian, Pascal Richette, Valérie Bousson, Hang Korng Ea.

 

Affiliation(s):

Viggo Petersen Center, Inserm Umr 1132 Bioscar, Lariboisière Hospital.

 

 

Introduction: Calcium pyrophosphate (CPP) crystals are extensively distributed throughout the musculoskeletal system, depositing in diverse structures including hyaline cartilage, fibrocartilage, ligament, and tendon. Despite this, their precise anatomical distribution remains poorly characterized.

Objectives: This study aims to determine the prevalence of CPP crystal deposition across various axial and peripheral joints, categorized by structural types.

Methods: Musculoskeletal CPP deposition was analyzed using whole-body low-dose computed tomography (CT) (Canon Prism) in 31 patients diagnosed with chondrocalcinosis of various etiologies. Within each anatomical site, deposits were categorized by structure: cartilage, fibrocartilage (e.g., menisci, intervertebral discs), ligament, and tendon. Twenty-three sites, including both peripheral and axial joints, were evaluated (Figure 1). An attenuation threshold of greater than 150 Hounsfield Units (HU) was used to define calcified tissue.

Results: The mean age of patient was 58.9 ± 13.9 years, with a female-to-male ratio of 2.7. Etiologies included 14 idiopathic cases, 14 associated with Gitelman syndrome, one with hyperparathyroidism, and one with an ANKH-activating mutation.

The average number of affected sites per patient was 9.2 ± 5.2, involving an average of 3.3 ± 1.0 different structural types. Peripheral joint involvement was present in 100% of patients, and cervical spine deposition was observed in 93.1%.

Cartilage: A mean of 5.1 ± 5.0 sites was affected per patient, predominantly involving the sternoclavicular joints (50% and 40%) and femorotibial joints (44.8% and 41.4%).

Ligaments: An average of 5.7 ± 3.9 sites was involved per patient, notably the transverse C1–C2 ligament (51.7%), the scapholunate and lunotriquetral ligaments (51.9%), and the posterior cruciate ligaments (50% and 41.4%)

Tendons: A mean of 2.6 ± 2.5 sites was affected per patient, primarily involving the knees and the Achilles tendons (≈40%).

Fibrocartilage: An average of 4.9 ± 3.1 sites was involved per patient, most frequently the knee menisci (62% and 69%), the pubic symphysis (65.5%), intervertebral discs (cervical 65.5%, thoracic 48.3%, lumbar 29.6%), and the triangular fibrocartilage complex (63% and 59.3%).

Conclusion: CPP crystal deposition was extensive and diffuse, involving both axial and peripheral joints. Cervical spine involvement was the most frequent finding. Mapping the distribution of deposits via whole-body low-dose CT (Figure 1) may help to better characterization and improved management of patients with chondrocalcinosis.

Keywords: Calcium pyrophosphate crystal, whole-body low-dose CT, deposits