Total-body 18F-FDG PET/CT in patients with inflammatory arthritis: initial findings using the uEXPLORER system

Purpose: Rheumatoid arthritis (RA) and psoriatic arthritis (PsA) are systemic autoimmune conditions that typically involve multiple joints and organs. Conventional 18F-FDG PET/CT scans have been infrequently used in RA and PsA and are commonly hampered by limitations, such as spatial resolution and sensitivity characteristics of conventional scanners, which limit the detection of synovitis and small lesions in the hand and feet joint. The high-sensitivity, high-resolution uEXPLORER, a 194-cm field-of-view total-body PET/CT scanner, is capable of examining the systemic burden of these conditions, across multiple joints and multiple organ systems. The scanner also has high spatial resolution of better than 3 mm. We describe initial findings from a prospective study using the uEXPLORER PET/CT scanner in patients with RA and PsA, with osteoarthritis (OA) controls. Methods: Patients with established RA, PsA or OA were prospectively enrolled in an IRB-approved study. All subjects underwent a single-timepoint total body uEXPLORER PET/CT scan for 20 minutes starting at 40 minutes after IV injection of 75.5±4.4 MBq of 18F-FDG (~1/5th of the conventional dose). Hand and foot immobilization aids were applied to limit subject movement. Images were reconstructed at 2.3 mm-voxel size. Qualitative findings and different patterns for the three conditions are described.

Results: This ongoing study recruited 14 patients, all males, with RA (n=3; 64-, 71- & 71-yrs), PsA (n=8; median age:68 [42-77yrs]), or OA (n=3; 40-, 50- & 71-yrs). The RA patients showed multiple, rather symmetric joint involvement, most commonly in the hands. The following sites were involved: radio- and/or ulno-carpal compartments (n=3), first interphalangeal (IP) (n=3) and first carpometacarpal joint (n=2), metacarpophalangeal (MCP) joints (n=2) and proximal IP joints (n=2). Joints of the feet appeared to be less frequently affected. Other notable features included enthesitis (n=3), increased fingertip (n=1) or fingernail FDG uptake (n=1) and the presence of deformity (n=1). All patients with PsA demonstrated multiple sites of enthesitis (n=8/8), which affected the tendons of the hand and fingers in all patients and seemed more active on the extensor side (n=3). Large joints showed positive findings in all patients. Less frequent features included sausage finger (n=1), hand deformity (n=1), plantar fasciitis (n=1) and affection of sacroiliac joint (n=2). Involvement of the interspinous ligament (n=1) and facet joints (n=1) was also noted. Patients with OA showed unilateral enhanced FDG uptake at least one big joint (shoulder, n=2; elbow, n=1; knee=1), small joints of the hand/feet (first MCP, n=1; metatarsophalangeal joint, n=1), and the quadriceps femoris tendon (n=2). Bilateral trochanteric bursitis was also noted (n=1). Enhanced FDG activity along the fingertips and nail beds was noticed (n=1). Conclusion: Systemic joint evaluation of study participants with inflammatory arthritis (RA, PsA) and osteoarthritis appears to be feasible using the uEXPLORER PET/CT total-body scanner. Careful definition and assessment of the patterns and distribution joint involvement across the body may provide further insight into the systemic inflammatory burden and pathogenesis of each of these conditions.

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