Ankylosing Spondylitis



Ankylosing Spondylitis


Scott Chandler, DO

Kevin deWeber, MD, FAAFP, FACSM, RMSK



BASICS


DESCRIPTION



  • Ankylosing spondylitis (AS) is a chronic inflammatory, autoimmune arthritis characterized by inflammatory back pain (IBP).


  • It is the most common and potentially severe subtype of spondyloarthritis (SpA), which includes:



    • Reactive (Reiter) arthritis.


    • Arthritis/spondylitis with inflammatory bowel disease (IBD).


    • Arthritis/spondylitis with psoriasis.


    • Unspecified spondylitis.


    • AS without confirmed radiographic findings is classified as nonradiographic axial spondyloarthropathy (nr-axSpA) and has similar outcomes and response to treatment.


  • AS causes inflammation of the sacroiliac (SI) joints, peripheral joints, and entheses (sites where ligaments or tendons attach to bone).


  • Common sites for enthesopathy include:



    • Calcaneus (Achilles and plantar fascia insertions).


    • Patella.


    • Tibial tubercle.


    • Vertebral bodies.


  • The involvement of vertebral body entheses leads to the characteristic findings of syndesmophytes (vertical bony growths) and eventual fusion, which are responsible for the classic radiographic “bamboo” appearance of the spine in advanced disease.


  • Synonym(s): axial spondyloarthritis; inflammatory spine disease


EPIDEMIOLOGY


Incidence



  • Overall incidence: 0.5 to 8.2/100,000/yr


  • Incidence rate varies directly with prevalence of human leukocyte antigen (HLA)-B27 in given population.


  • Commonly presents in young adulthood


  • Predominant age:



    • 80% of patients with AS develop symptoms before age 30 yr.


    • < 5% of patients with AS present after age 45 yr.


  • Predominant gender: male > female (˜3:1)


Prevalence



  • Prevalence of AS is 9 to 30/10,000 depending on HLA-B27 prevalence in the population (1).


  • Higher in Alaskan Eskimos and some Native American populations owing to higher than average HLA-B27 rate


  • Lower in African Americans secondary to a lower HLA-B27 rate


  • Up to 5% of patients evaluated for chronic low back pain are ultimately diagnosed with AS.


ETIOLOGY AND PATHOPHYSIOLOGY



  • A clear etiologic pathway has not been established.


  • Speculated that an environmental/infectious trigger in a genetically susceptible individual leads to an inflammatory (T cell and macrophage) immune response that specifically targets SI, peripheral joint, and enthesis inflammation, eventually causing bony proliferation, erosions, sclerosis, and joint destruction.


Genetics



  • Expression of HLA-B27 antigen is clearly linked to the development of AS, but the exact mechanism is unknown.


  • Prevalence of HLA-B27 in African Americans is 2-4% and in Caucasians is 8%.


RISK FACTORS



  • Positive family history of SpA or HLA-B27


  • 90% or more of individuals with AS are HLA-B27 positive, although an individual who is HLA-B27 positive has a 5% chance of having AS.


  • Reactive arthritis triggered by Chlamydia trachomatis and certain enteric infections (e.g., Shigella, Salmonella, Yersinia, and Campylobacter spp.) predisposes to development of AS.



COMMONLY ASSOCIATED CONDITIONS



  • Enthesitis—29% (2)


  • Uveitis/iritis—23%


  • Psoriasis—10%


  • Dactylitis—6%


  • IBD—4%


  • Rarely, cardiac valve/aortic root involvement


Mar 14, 2020 | Posted by in SPORT MEDICINE | Comments Off on Ankylosing Spondylitis
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