Classification of spondyloarthritides (SpA) & USpA

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Classification of spondyloarthritides (SpA) & USpA
Definition: The spondyloarthritides (SpA) are an interrelated group of rheumatic diseases that are characterized by common clinical symptoms and genetic similarities.

For clinical purposes, 5 subgroups are differentiated:
1.    AS (ankylosing spondylitis)
2.    Psoriatic SpA (PsSpA)
3.    Reactive SpA (ReSpA)
4.    SpA associated with inflammatory bowel disease (SpAIBD) and
5.    Undifferentiated SpA (uSpA)

Features of SpA:

Important clinical features of the SpA are
1.    inflammatory back pain (IBP)
2.    asymmetric peripheral oligoarthritis predominantly of the lower limbs
3.    enthesitis
4.    specific organ involvement such as anterior uveitis (eye) , psoriasis (skin) and chronic inflammatory bowel disease

The most important subtype of SpA is ankylosing spondylitis (AS), which is now considered part of axial spondyloarthritis.
ASAS Classification: ASAS stands for Assessment of SpondyloArthritis International Society. 
ASAS group has recently developed criteria to classify patients with axial SpA with or without radiographic sacroiliitis, and criteria to classify patients with peripheral SpA.

Axial SpA:
1. LBA (>3 months almost every day)
2. Radiographs and magnetic resonance imaging (MRI can detect active inflammation and structural damage associated with SpA.)
3. HLA-B27 (Leucocyte antigen): SpA are genetically linked (90% of cases), the strongest contributing factor being HLA B27.
According to the ASAS axial SpA criteria, patients with chronic back pain aged less than 45 years at onset can be classified as having axial SpA if sacroiliitis on imaging (radiographs or MRI) plus 1 further SpA feature are present, or if HLA-B27 plus 2 further SpA features are present.

Peripheral SpA:
1. Patients with peripheral arthritis (usually asymmetric arthritis predominantly involving the lower limbs) enthesitis, or dactylitis.
2. Patients can be classified as having peripheral SpA if 1 of the following features is present: uveitis, HLA-B27, preceding genitourinary or gastrointestinal infection, psoriasis, inflammatory bowel disease, sacroiliitis on imaging (radiographs or MRI) in addition to point no 1.
3. Or if 2 of the following features besides the entry feature are present: arthritis, enthesitis, dactylitis, inflammatory back pain, or a positive family history of SpA.

USpA

Clinical features of USpA:
Vast majority of USpA have IBP (Inflammatory back pain) & asymmetrical peripheral arthritis predominately of lower limbs.

HLA B27 is more helpful uSpA diagnosis: Liao et al analysed the clinical features of Chinese undifferentiated spondyloarthritis (USpA) patients with predominantly axial involvement. They found in Chinese population Both HLA-B27 status and SIJ MRI findings influence the classification of Chinese axial USpA patients, but HLA-B27 seems of more value.

References:
1. Braun J & Sieper J; Z Rheumatol. 2010 Jul;69(5):425-32; quiz 433-4. Spondyloarthritides.
2. van den Berg R & van der Heijde DM; Pol Arch Med Wewn. 2010 Nov;120(11):452-7. How should we diagnose spondyloarthritis according to the ASAS classification criteria: a guide for practicing physicians.
3. Liao Z et al; Scand J Rheumatol. 2011 Nov;40(6):439-43. Epub 2011 Jul 4. Clinical features of axial undifferentiated spondyloarthritis (USpA) in China: HLA-B27 is more useful for classification than MRI of the sacroiliac joint.
4. http://www.medscape.org/viewarticle/545412_2

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