Table. Characteristics and MRI Findings of Patients With Immune Checkpoint Inhibitor Induced Inflammatory Arthritis.

Patient No./Sex	Primary Tumor	ICI	ICI Type	Preexisting Joint Disease	Onset of Symptoms, wka	Time From Symptom Onset to MRI, wk	Autoantibody Test Resultsb	Acute Phase Reactantsc	Findings			Antitumor Response	IA Management
									MSK Examination	Radiographic	MRI
1/M	Kaposi sarcoma	Pembrolizumab	Anti–PD-1	Tendinopathy (shoulder)	2	18	Negative for RF, CCP, ENA, and ANA	CRP = 13.3 mg/L; ESR = 51 mm/h	Dactylitis, limited passive to active ROM of shoulders, and synovitis in wrists, MCPs, and PIPs	Shoulders: AC joint OA; knee: small effusion; wrists, hands, and feet: unremarkable	Hand: tenosynovitis of bilateral flexor tendons (first though fourth)	Complete	ICI therapy discontinued and high-dose corticosteroids (1 mg/kg) administered with slow taper
2/M	Thyroid cancer	Pembrolizumab	Anti–PD-1	Tendinopathy (shoulder), metastatic disease (pelvis)	4	1	CCP >125; RF =  84; negative for ANA and ENA	CRP = 270 mg/L; ESR = 127 mm/h	Shoulder IA (BL), left biceps tendinitis, first extensor compartment tenosynovitis, effusion in knees, and synovitis in elbows, wrists, PIPs, and knees;	Wrists and hands: Periarticular osteopenia and erosions; left shoulder: unremarkable; feet: degenerative changes	Hand: synovitis of fourth and fifth MCP joint, marginal erosions, and tenosynovitis of the extensor and flexor compartment; periarticular marginal bone marrow edema in carpals and metacarpals	Progressive disease	ICI therapy held; good response to 20 mg/d for 2 wk followed by taper
3/F	Urothelial carcinoma	Nivolumab	Anti–PD-1	OA (hands and knees)	16	9	Negative for RF, CCP, ENA, and ANA	CRP = 6 mg/L; ESR = 57 mm/h	Bilateral first extensor compartment tenosynovitis and arthralgias of wrists, hands, shoulders, knees, and feet	Wrists and hands: degenerative changes	Hand: tenosynovitis of first and sixth extensor compartments	Stable disease	ICI therapy held briefly and high-dose acetaminophen and occupational therapy administered
4/F	Cervical cancer	Nivolumab	Anti–PD-1	None	4	80	Negative for RF, CCP, ENA, and ANA	CRP = 11.3 mg/L; ESR = 48 mm/h	Elbow contractures, restricted subtalar motion, swan neck deformities, effusion in knees, and synovitis in knees, MCPs, PIPs, and wrists	Wrists and hands: joint deformities and diffuse osteopenia; feet and ankles: periarticular osteopenia and bilateral pes planus	Hand: multifocal osseous erosions involving distal radius, distal ulna, carpal bones, and metacarpal bones, synovitis of intercarpal joints, tenosynovitis involving the flexor and extensor tendons at the wrist	Stable disease	NSAIDs and intraarticular corticosteroids administered
5/F	Colon cancer	Avelumab	Anti–PD-L1	None	28	16	ANA = 4.4 ELISA units; negative for dsDNA, ENA, RF, and CCP	CRP = 10.7 mg/L; ESR = 38 mm/h	Effusion in knees and synovitis in wrists, MCPs, PIPs, and knees	NP	Hand: no erosions, tenosynovitis, or synovitis	Progressive disease	Held ICI therapy, prednisone administered with taper, and ICI shortly thereafter discontinued given disease progression
6/F	Pheochromocytoma	Nivolumab and ipilimumab	Anti–PD-1 and anti–CTLA-4	None	24	2	Negative for RF, CCP, ENA, and ANA	CRP = 127 mg/L; ESR = 100 mm/h	Effusion in knees and synovitis in knees and right wrist	NP	Knee: moderate effusion and diffuse thickening of synovium	Progressive disease	Held ICI therapy and therapeutic arthrocentesis, intraarticular corticosteroids, and prednisone 20 mg administered followed by taper
7/F	Cervical cancer	Bintrafusp alfa	Anti–PD-L1 and TGF-βRII trap	None	44	24	ANA = 2.3 ELISA units; negative for RF and CCP	CRP = 107 mg/L; ESR = 111 mm/h	Effusion and synovitis in left ankle and knees	Bilateral knees: minimal degenerative changes; bilateral ankles: soft-tissue swelling	Ankle: complex joint effusion, thickening of tibiotalar joint synovium, and peroneal tenosynovitis	Complete	ICI stopped approximately 6 wk prior to symptom onset owing to another irAE, prednisone 20 mg administered, and methotrexate added given inability to wean steroids
8/F	Lung cancer	Bintrafusp alfa	Anti–PD-L1 and TGF-βRII trap	Seronegative RA	1	13	ANA = 3 ELISA units; negative for RF, CCP, and ENA	CRP = 8.4 mg/L; ESR = 62 mm/h	AC joint warmth, TTP, first compartment tenosynovitis, and synovitis in wrists, MCPs, and PIPs	Hands and wrists: multifocal erosions; shoulders: unremarkable; knees: subtle narrowing of medial compartment on left side	Hand: erosions at the radial styloid and carpal bones; wrist: synovitis and tenosynovitis of the flexor and extensor tendons	Partial	ICI continued and NSAIDs administered for IA

Abbreviations: AC, acromioclavicular; ANA, antinuclear antibody; BL, bilateral; CCP, cyclic citrullinated peptide; CRP, C-reactive protein; CTLA-4, anti-cytotoxic T-lymphocyte-associated protein-4; dsDNA, double-stranded DNA; ENA, extractable nuclear antigen; ELISA, enzyme-linked immunosorbent assay; ESR, erythrocyte sedimentation rate; F, female; IA, inflammatory arthritis; ICI, immune checkpoint inhibitor; irAE, immune-related adverse event; M, male; MCP, metacarpophalangeal; MRI, magnetic resonance imaging; MSK, musculoskeletal; NP, not performed; NSAID, nonsteroidal anti-inflammatory drug; OA, osteoarthritis; PD-1, programmed cell death-1; PD-L1, programmed cell death ligand 1; PIP, proximal interphalangeal; RA, rheumatoid arthritis; RF, rheumatoid factor; ROM, range of motion; TGF-βRII, transforming growth factor β receptor II; TTP, tenderness to palpation.

SI conversion factor: To convert CRP to nanomoles per liter, multiply by 9.524.

^aIndicates the time between initiation of ICI therapy and the onset of MSK joint pain.

^bLaboratory thresholds for negative results: RF, less than 15 ELISA units; CCP, less than 20 ELISA units; ANA, less than 1 ELISA units; ENA, less than 20 ELISA units. Inflammatory markers were obtained at the time of initial rheumatologic evaluation.

^cReference ranges for ESR, 0 to 25 mm/h; for CRP, 0 to 4.99 mg/L.