Dr. Rosenthal shared an update on the association of osteoporosis with CPP deposition. In a study from her team evaluating 25,000 patients with CPP deposition, the relative risk of osteoporosis was increased compared with an age-matched population.1
“Interestingly, some of the well-known metabolic syndromes associated with CPP deposition, including hemochromatosis and hypophosphatasia, are also associated with osteoporosis, and hyperparathyroidism causes increased bone remodeling,” she said. These associations emphasize the burgeoning importance of bone in CPP deposition.
Other key clinical observations in the form of case reports have demonstrated that CPP deposition can occur in weird places, Dr. Rosenthal said, such as soft tissue deposits in the spine, and in the temporomandibular joint. Common triggers of acute CPP attacks include illness or surgery.
Medications may also trigger CPP attacks, including, somewhat controversially, diuretics, as well as tacrolimus and immunomodulatory chemotherapies. She said a fairly robust collection of articles has evaluated bisphosphonates as potential triggers in acute CPP arthritis, but considering the increased prevalence of osteoporosis in the population with CPP deposition, one wonders if this could be confounding by indication.2
Diagnostic Modalities to Identify CPP Deposition
There’s some light on the horizon, with diagnostics that may help rheumatologists better manage CPP arthritis, Dr. Rosenthal noted.
CPP crystals are hard to see and many lack birefringence, including needle-shaped CPP crystals, as discussed in research from Andrés et al.3 Dr. Rosenthal shared several microscopy tips to better identify CPP crystals, such as:
- Avoid collecting synovial fluid in ethylenediamine tetraacetic acid (EDTA)-containing collecting tubes;
- Turn off the polarizer and turn up the light;
- Use oil or the highest power available;
- Use phase contrast if possible; and
- Take your time.
“Newer crystal identification modalities are on the horizon, such as a lens-free holographic polarized microscope system that is getting better for identifying CPP crystals and may eventually be an app on your cell phone,” she said.
Dr. Rosenthal also reviewed patient imaging modalities in order of usefulness for identifying CPP deposition. Conventional radiography can identify tendon calcifications that show important clues to identifying CPP deposition. Ultrasound may be slightly more sensitive than plain radiographs for diagnosing chondrocalcinosis, but requires a trained eye to distinguish the changes from those of gout. Additionally, conventional computed tomography (CT) scanning and dual-energy CT scanning hold promise for identifying CPP deposition. A study by Pascart et al. demonstrated the ability of dual-energy CT to differentiate CPP crystals from the calcium phosphate crystals that appear in bone.5
