Table 1:
Comparison of clinical features between ICI-IA, RA, and SpA
| RA | SpA* | ICI-IA | |
|---|---|---|---|
| Epidemiology | 2–3 times more common in women | AS more common in men | Even gender distribution |
| Incidence peaks in 30s-50s | Axial SpA most commonly presents before age 40 | Adults 30s-80s exposed to ICI therapy | |
| Time from exposure to development ranges from weeks-years | |||
| Risk Factors | Tobacco smoke | GI/GU infections (ReA) | Largely unclear |
| Periodontal disease | Obesity (PsA) | Combination or long duration ICI therapy, multiple irAEs (persistent ICI-IA) | |
| Joint involvement | Small and large joints; classically MCPs, PIPs, wrists | Some subtypes have oligoarthritis, lower extremity predominant | Various subtypes: polyarthritis, large joint oligoarthritis |
| Axial disease rare except for C1–2 | Axial disease can be seen in all subtypes | Rare reports of axial disease (sacroiliitis) | |
| Imaging findings | Ultrasound: synovitis (Doppler positive); small and large joint effusions; tenosynovitis | MRI: Sacroiliitis with bone marrow edema, erosions, and sclerosis | Ultrasound: synovitis (Doppler positive); small and large joint effusions; enthesitis; enthesophytes |
| Radiographs: erosions and joint space narrowing | Radiographs: facet or SI joint ankylosis; syndesmophytes; juxta-articular bone formation (PsA) | Radiographs: erosions can be observed within months of symptoms (rare) | |
| Extra-articular disease | Interstitial lung disease common, can be subclinical | Some subtypes associated with GI inflammation (IBD associated, ReA) | Concurrent colitis reported in those on combination ICI therapy |
| Increased risk for lymphoma, lung cancer | Skin psoriasis can be seen in all subtypes | Multiple irAEs common | |
| Ocular: scleritis | Ocular: uveitis | Ocular: uveitis, may not be concurrent with IA | |
| Prognosis | Chronic; requires long term treatment with DMARDs | Most subtypes are chronic | Varies: some self-limited but others persist |
| Common to have disability in 2–3 years if untreated | ReA self-limited in > 90% | Bone damage within months of symptom onset reported | |
*
Includes AS (ankylosing spondylitis) as well as axial, IBD (inflammatory bowel disease)-associated, and undifferentiated SpA (spondyloarthritis), ReA (reactive arthritis), and PsA (psoriatic arthritis); RA (rheumatoid arthritis); ICI-IA (immune checkpoint inhibitor-induced inflammatory arthritis); irAE (immune related adverse event); DMARD (disease modifying anti-rheumatic drug); MRI (magnetic resonance imaging)