Ultrasound-detected inflammation and structural changes in the joints, tendons and entheses of patients with cancer who developed arthritis or arthralgia after exposure to immune checkpoint inhibitors.

[OBJECTIVES] To explore the prevalence and distribution of ultrasound-detected inflammation and structural damage in the joints, tendons and entheses of patients who developed new-onset arthritis or arthralgia following exposure to immune checkpoint inhibitor (ICI) therapy, including a comparison between those with ICI-induced arthritis and those with ICI-induced arthralgia.

[METHODS] Patients with cancer who developed clinical arthritis or arthralgia (ie, joint pain without clinical synovitis) after receiving ICIs were consecutively recruited from six international centres. Patients underwent a full clinical assessment and ultrasound evaluation of 18 joints, 15 tendons and 5 entheses bilaterally, using the Outcome Measures in Rheumatology definitions.

[RESULTS] A total of 101 patients were included: 53 (52.5%) had ICI-arthralgia (absent clinical synovitis). Among them, 25 (47.2%) had ultrasound-detected subclinical synovitis, 10 (18.9%) tenosynovitis, 1 (1.9%) digital extensor peritendinitis and 13 (24.5%) enthesitis. In the 48 patients with ICI-arthritis, ultrasound-detected synovitis was more prevalent than in ICI-arthralgia (93.8% vs 47.2%, p<0.001), particularly in the wrists (56.3% vs 20.8%, p<0.001) and the knees (54.2% vs 13.2%, p<0.001), which were the most frequently affected joints. Tenosynovitis (52.1% vs 18.9%, p<0.001), peritendinitis (10.4% vs 1.9%, p=0.099) and bone erosions (25% vs 7.5%, p=0.027) were also more frequent in ICI-arthritis. 'Active' enthesitis was similar between groups (31.3% vs 24.5%), with no significant differences.

[CONCLUSIONS] This multicentre study reveals a higher burden of ultrasound-detected changes in ICI-arthritis compared with ICI-arthralgia, with diverse patterns across joints, tendons and entheses in both subtypes. Significant subclinical inflammation suggests that many cases of non-specific ICI-arthralgia may benefit from targeted interventions.