Table 3.

Axial and peripheral spondyloarthritis Assessment of Spondyloarthritis International Society classification criteria

Axial spondyloarthritis ref. [11]		Peripheral spondyloarthritis ref. [12]
Individuals <45 years with back pain >3 months*		Individuals with arthritis or enthesitis or dactylitis
Imaging	HLA-B27
Sacroiliitis on MR or X-rays	Positive test
Additional features needed for classification§
At least one	At least two	At least one	At least two
Inflammatory back pain		Uveitis	Arthritis
Arthritis		Psoriasis	Enthesitis (heel pain)
Enthesitis (heel pain)		Crohn’s/colitis	Dactylitis
Uveitis		Previous infection	Inflammatory back pain (ever)
Dactylitis		HLA-B27	Family history for SpA
Psoriasis		Sacroiliitis on imaging
Crohn’s/colitis
Good response to non-steroidal antinflammatory drugs
Family history for spondyloarthritis
HLA-B27
Elevated C reactive protein

Classification of individuals as Axial SpA: *Requires two eligibility criteria (age at onset and duration of back pain) followed by two different approaches, one through MR and another through HLA-B27 testing. The former requires at least one and the latter at least two additional criteria.

Classification of individuals as peripheral SpA: Requires at least of three eligibility criteria (arthritis or enthesitis or dactylitis) plus one or two items depending on their diagnostic value.

§Despite axial and peripheral SpA share most additional criteria for classification, the definition of some individual criteria might be different. Please check such definitions in tables.

MR = Magnetic Resonance.