Table 1.

Main differences between ICI-induced rheumatic syndromes and their idiopathic counterparts.

RA	ICI-Induced Arthritis
Usually involves small joints of the hands in a symmetrical fashion	May manifest as mono, oligo or polyarthritis
Synovium is primarily targeted	Apart from synovitis, myo-fasciitis may be prominent
Responds to steroids but treatment with DMARDs is always needed	Good response to steroids DMARD needed when relapse occurs during steroid tapering
PMR	ICI-Induced PMR
Aching and stiffness in the shoulder and pelvic girdles are typical symptoms	Joint involvement, including knees and hands, may occur
High inflammatory markers are a diagnostic criterion	Absence of increased inflammatory markers is reported in several cases
Responds to low dose of steroids (prednisolone, 20 mg/daily)	Aggressive treatment with higher doses of steroids may be needed
Polymyositis/Dermatomyositis	ICI-Induced Myositis
Typical clinical presentation involves proximal muscle weakness, without associated muscle pain, sparing facial muscles Dermatomyositis exhibits typical rash	May present with myalgia and oculomotor symptoms, while typical rash is usually absent
Increase in muscle enzymes and autoantibodies against nuclear or cytoplasmic antigens aid diagnosis	May exhibit significant increase in muscle enzymes, albeit normal in a subset of patients Autoantibodies are usually absent
High-dose steroids are the mainstay of treatment Additional immunosuppression is needed in resistant disease and extramuscular features such as ILD	High-dose steroids are usually required, even though milder clinical phenotypes respond well to moderate doses Increased frequency of concurrent myasthenia and/or cardiac involvement is reported and may warrant additional immunosuppression
Systemic Vasculitides	ICI-Induced Vasculitis
High inflammatory burden is typical Autoantibodies, such as ANCA, can aid diagnosis in subsets of the disease	Inflammatory markers are commonly increased, but autoantibody positivity is rare
Sjogren Syndrome	ICI-Induced Sicca
Striking female preponderance	Male predominance in some case series
Specific autoantibodies are typically positive	Absence of autoantibodies is reported in most cases
Dry eyes and dry mouth are the most frequent complaints	Dry mouth is the most prominent symptom
SLE	ICI-Induced Lupus
Typically affects females of childbearing age Antinuclear antibodies are almost always positive	Older age, lack of striking female predominance and absence of autoantibodies are reported

ICI = immune checkpoint inhibitor, RA = rheumatoid arthritis, PMR = polymyalgia rheumatica, ILD = interstitial lung disease, ANCA = antineutrophil cytoplasmic antibodies, DMARDs = disease-modifying antirheumatic drugs, SLE = systemic lupus erythematosus.