|Classification and external resources|
|ICD-10||M40 through M54|
|ICD-9||720, 721, 722, 723, 724|
Spondyloarthropathy is any joint disease of the vertebral column. As such, it is a class or category of diseases rather than a single, specific entity. It differs from spondylopathy, which is a disease of the vertebra itself. However, many conditions involve both spondylopathy and spondyloarthropathy.
Spondyloarthropathy with inflammation is called spondylarthritis. In the broadest sense, the term spondyloarthropathy includes joint involvement of vertebral column from any type of joint disease, including rheumatoid arthritis and osteoarthritis, but the term is often used for a specific group of disorders with certain common features, the group often being termed specifically seronegative spondylarthropathies. They have an increased incidence of HLA-B27, as well as negative rheumatoid factor and ANA. Enthesopathy is also sometimes present in association with seronegative spondarthritides.
Nonvertebral symptoms of spondyloarthropathies include asymmetric peripheral arthritis (which is distinct from rheumatoid arthritis), arthritis of the Toe IP Joints, sausage digits, achilles tenosynovitis, plantar fasciitis, costochondritis, iritis, and mucocutaneous lesions. However, lower back pain is the most common clinical presentation of the disease; this back pain is unique because it decreases with activity.
Seronegative spondyloarthropathy 
"Seronegative" refers to the fact that these diseases are negative for rheumatoid factor, indicating a different pathophysiological mechanism of disease than what is commonly seen in rheumatoid arthritis.
The following conditions are typically included within the group of seronegative spondylarthropathies:
|Condition||Percent of people with the
condition who are HLA-B27 positive
|Reactive arthritis (Reiter's syndrome)||60-80%|
|enteropathic spondylitis or spondylitis associated with
|Isolated acute anterior uveitis||50%|
|Undifferentiated spondyloarthropathy (USpA)||20-25%|
Common characteristics 
These diseases have the following conditions in common:
- They are in relation to HLA-B27
- Inflammatory arthritis, generally sacroiliitis and spondylitis
- Oligoarthritis, generally with asymmetrical presentation
- Enthesitis (inflammation of the entheses, the sites where tendons or ligaments insert into the bone.)
- familial aggregation occurs
- rheumatoid factor is not present
- Extra-articular features, such as involvement of eyes, skin and genitourinary tract
- Overlap is likely between several of the causative conditions
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