Role of PET/CT in diagnosing and monitoring disease activity in rheumatoid arthritis: a review

Abstract

Rheumatoid Arthritis (RA) is a systemic inflammatory disorder that commonly presents with polyarthritis but can have multisystemic involvement and complications, leading to increased morbidity and mortality. The diagnosis of RA continues to be challenging due to its varied clinical presentations. In this review article, we aim to determine the potential of PET/CT to assist in the diagnosis of RA and its complications, evaluate the therapeutic response to treatment, and predict RA remission. PET/CT has increasingly been used in the last decade to diagnose, monitor treatment response, predict remissions, and diagnose subclinical complications in RA. PET imaging with [¹⁸F]-fluorodeoxyglucose ([¹⁸F]-FDG) is the most commonly applied radiotracer in RA, but other tracers are also being studied. PET/CT with [¹⁸F]-FDG, [¹⁸F]-NaF, and other tracers might lead to early identification of RA and timely evidence-based clinical management, decreasing morbidity and mortality. Although PET/CT has been evolving as a promising tool for evaluating and managing RA, more evidence is required before incorporating PET/CT in the standard clinical management of RA.

Keywords: Diagnosis; Fibroblast activation protein inhibitor (FAPI); Monitoring; Positron emission tomography/computed tomography (PET/CT); Rheumatoid arthritis (RA); [18F]-fluorodeoxyglucose ([18F]-FDG); [18F]-sodium fluoride ([18F]-NaF).

Fig. 1

[¹⁸F]-FDG PET/CT was performed on a 71-year-old female with rheumatoid arthritis for seven years and was experiencing a flare-up. Maximum intensity projection (MIP) images of [¹⁸F]-FDG PET/CT in the anterior and right lateral views are shown in (a). Axial images of the atlantoaxial joint are shown in (b) (from top to bottom: PET, CT, and fused PET/CT). Atlantoaxial joint, right and left axillary lymph nodes, knees, hips, carpals, wrists, elbows, and shoulders all showed significant [¹⁸F]-FDG uptake. Reproduced with permission from [25]

Fig. 2

In this [¹⁸F]-NaF PET/CT study, regions of interest were manually outlined around the abdominal aorta, as shown in green. Comparison was made between the abdominal aortic wall of a 63-year-old patient with rheumatoid arthritis and an age- and sex-matched healthy control. The [¹⁸F]-NaF PET/CT scan revealed higher levels of [¹⁸F]-NaF activity in the abdominal aorta of the RA patient when compared to the healthy control. With permission from reference [20]

Fig. 3

The above image demonstrates the PET/CT appearance of lung nodules, both benign and malignant, in patients with rheumatoid arthritis. The images were presented in three rows: the top row showed maximum intensity projection, the middle row showed fused PET/CT, and the bottom row showed CT scans. [¹⁸F]-FDG PET/CT images of rheumatoid arthritis patients with histologically proven rheumatoid nodules appeared as multiple, well-defined solid nodules located peripherally, with low [¹⁸F]-FDG activity (indicated by green arrows), in contrast to the appearances of squamous cell carcinoma (b), adenocarcinoma (c), and pulmonary carcinoid (d). With permission from reference [50]

Fig. 4

The study examined joint inflammation using [¹⁸F]-FDG PET/CT in a patient with rheumatoid arthritis at baseline (A) and after 12 months of tofacitinib treatment (B). The maximum intensity projection PET/CT image at baseline (A) displayed increased synovial activity in multiple joints, including the wrists, small hand joints, elbows, and knees bilaterally. However, in the follow-up image (B), after 12 months of tofacitinib treatment, there was a decrease in [¹⁸F]-FDG uptake, indicating a reduction in joint inflammation. With permission from reference [60]

Fig. 5

[¹⁸F]-FDG PET/CT images demonstrating aortic inflammation in patients with RA at baseline (A, C) and after therapy (B, D) with tofacitinib. With permission from reference [60]