Non-invasive characterization of intra-articular mineralization using dual-energy computed tomography

A 65-year-old man presented with acute onset right knee pain. His regular treatment included azacitidine for the management of secondary myelodysplastic syndrome. Physical examination showed swelling, warmth and tenderness in the right knee, with limping. Laboratory tests revealed high CRP and ferritin levels. Serum levels of urate, calcium, phosphate and magnesium as well as rheumatoid factor and anti-citrullinated protein antibodies assays were normal. Synovial fluid analysis identified an inflammatory cell count with characteristic calcium pyrophosphate (CPP) crystals, but no evidence of monosodium urate or basic calcium phosphate (BCP) crystals or septic arthritis. Conventional radiography (Fig. 1A) and CT (Fig. 1B) showed chondrocalcinosis without osteoarthritic changes and subtle marginal erosion of the medial tibial plateau. Dual-energy CT (DECT) revealed coexisting CPP and BCP crystal deposits, in particular in calcifications with intraosseous migration (Fig. 1C). The patient was treated with intra-articular betamethasone, providing rapid symptom relief. Identifying BCP crystals requires advanced methods such as diffraction techniques or rotational-vibrational spectroscopy, which are not widely available clinically. Although coexistence of BCP and CPP crystals has been proven in osteoarthritic knees ex vivo, DECT has recently shown promise in the non-invasive characterization of articular calcium crystal deposits in vivo [1]. Advances in DECT technology [1] and emerging multi-energy photon-counting CT [2] may provide new insights by clarifying the role—innocent bystander and/or advanced osteoarthritis marker vs active player in cartilage damage by triggering oxidative stress—played by intra-articular mineralization in crystal arthropathies and osteoarthritis. Conventional radiography, CT and DECT images of the right knee (A) Anteroposterior radiograph and (B) coronal-reformatted CT images show chondrocalcinosis (white arrowhead) in the medial and lateral tibiofemoral and proximal tibiofibular joint spaces, without osteoarthritic changes, but with subtle marginal erosion of the medial tibial plateau (arrow). (C) Three-dimensional volume-rendered DECT image reveals coexisting CPP (color-coded in red) and BCP (color-coded in blue) crystal deposits, with BCP crystal aggregates exhibiting specific DECT attenuation characteristics and being found in particular in calcifications with intraosseous migration (yellow arrowhead). Funding: No specific funding was received from any funding bodies in the public, commercial or not-for-profit sectors to carry out the work described in this article. Disclosure statement: MH is an employee of GE Healthcare. The other authors have declared no conflicts of interest.