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Spondyloarthritis

John D. Reveille

The term spondyloarthritis (SpA) (otherwise known as spondylo- for peripheral spondyloarthritis based on the presence of
arthropathy) encompasses a heterogeneous group of inflammatory peripheral arthritis, enthesitis, or dactylitis have also been
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diseases characterized by spinal and peripheral joint arthritis, developed utilizing these innovations. The result of this is a
inflammation of the attachments of ligaments and tendons to reclassification of all the various spondyloarthritides under the
bones (enthesitis), and, at times, mucocutaneous, ocular, and/or diagnoses of axial and peripheral SpA.
cardiac manifestations. These disorders show familial aggregation
and are typically associated with genes of the major histocompat- EPIDEMIOLOGY
ibility complex (MHC), particularly human leukocyte antigen
(HLA)-B27 (Chapter 5). The SpA spectrum includes (i) axial The frequency of SpA in general and AS in particular varies in
spondyloarthritis (AxSpA), including ankylosing spondylitis different populations and parallels the frequency of HLA-B27.
(AS); (ii) reactive arthritis (ReA), known previously as Reiter The prevalence of AS varies from 0.2% to 0.7% among
syndrome; (iii) psoriatic arthritis (PsA) and/or spondylitis; (iv) people of European ancestry 8-10 and has been reported in
enteropathic arthritis and/or spondylitis associated with the similar frequencies in eastern Asia (Table 57.2). Higher rates
inflammatory bowel diseases (IBD), ulcerative colitis (UC), of prevalence have been reported in Eskimo groups from
or Crohn disease (CD); and (v) undifferentiated SpA, which Siberia and Alaska as well as in groups from Scandinavia and
encompasses patients expressing elements of, but failing to as high as 4.3% in male Haida Native Canadian groups, where
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fulfill, accepted criteria for one of the above diseases. In addition, the frequency of HLA-B27 is 50%. AS is much less frequent
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isolated acute anterior uveitis (AAU) and spondylitic heart disease in persons of African and Japanese descents, in whom HLA-B27
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(complete heart block and/or lone aortic regurgitation) associ- is rare.
ated with HLA-B27 may also be classified within the spectrum The prevalence of ReA is unknown and probably varies
of SpA. over time, depending on endemic rates of the sexually acquired
(Chlamydia) and enteric (Shigella, Salmonella, Campylobacter)
CLASSIFICATION OF SPONDYLOARTHRITIS infections that trigger it. It appears that the frequency of ReA
has dramatically declined following the adoption of safer sexual
There are no diagnostic criteria for any of the SpA types. Clas- practices and better sanitation, at least in Western countries, in
sification criteria have been developed to provide greater specificity the wake of the human immunodeficiency virus (HIV) epidemic.
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in clinical studies. The European Spondyloarthropathy Study Psoriasis affects 1–3% of the general population. The fre-
Group (ESSG) criteria for SpA were developed in 1991, have quency of PsA is less clear and is higher in those with more
been validated in numerous population groups, and remain the severe disease; population studies among Caucasians estimate a
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basis of many clinical and epidemiological studies (Table 57.1). frequency of approximately 0.1%. 8
The modified New York criteria, developed in 1966 and modified The prevalence of IBD is 100–200 per 100 000 among Cau-
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8,10
in 1984, remain the “gold standard” for AS. However, this depends casians, with an equal male-to-female ratio. It is rare in people
on the presence of radiographic sacroiliitis, which takes up to of African and Asian descents. The risk of spondylitis and
10 years to develop after the onset of inflammatory back pain. peripheral arthritis varies in different reports, perhaps reflecting
For PsA, the classification criteria for psoriatic arthritis (CASPAR) the subspecialty of the observer. Spondylitis occurs in as many
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(see Table 57.1) have stemmed from the perception that the as 15–20% of those with IBD. In general, peripheral arthritis
ESSG criteria were not “sensitive” enough. occurs less frequently in those with UC (up to 10%) than
The International League Against Rheumatism (ILAR) juvenile in those with CD (up to 20%), although its frequency tends to
idiopathic arthritis (JIA) classification criteria for enthesitis-related be higher in series where the assessor was a rheumatologist. 8,10
arthritis (ERA) have been proposed for juvenile SpA (JSpA; see
Table 57.1). No criteria have been validated for enteropathic
arthritis. PATHOGENESIS
New criteria have been developed by the Assessment of
SpondyloArthritis International Society (ASAS) for axial SpA Genetics of Spondyloarthritis
based on the presence of inflammatory back pain that take Familial Aggregation
advantage of imaging innovations, such as magnetic resonance Susceptibility to AS is clearly attributable to genetic factors, with
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imaging (MRI) and HLA-B27 typing. More recently, criteria a sibling recurrence risk ratio as high as 82 and twin-based studies
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