Spondyloarthritis (SpA) refers to a family of closely related diseases that share common features – chief among them being inflammatory arthritis in the spine and other joints. Spondyloarthritis often begins in young people, with symptoms usually starting before age 45.
Over 3.2 million adults in the U.S. have a form of SpA, making it more common than rheumatoid arthritis (RA), multiple sclerosis (MS), and amyotrophic lateral sclerosis (ALS), combined.
These conditions are currently grouped into two overlapping categories:
A person may have both axial and peripheral symptoms. The predominant symptoms (whether they are axial or peripheral) will determine the category, and the specific diagnosis.
A hallmark symptom of axial spondyloarthritis (axSpA) is inflammatory back pain, frequently characterized by a dull ache felt deep in the lower back, or buttocks. It is associated with inflammation of the sacroiliac (SI) joints, which are the joints linking the lowest part of the spine to the pelvis.
Inflammatory back pain usually begins before age 45, develops gradually, persists longer than three months, improves with physical activity but not rest, and can cause stiffness in the morning that lasts 30 minutes or longer. Though the lower back is usually impacted first, in some people inflammatory pain can start in the neck, or other areas. Other joints and organs can also become involved, including the hips, shoulders, eyes (iritis), gut (inflammatory bowel disease), and skin (psoriasis).
AxSpA is a broad category that includes people with and without characteristic bone changes or fusion in the spine. Doctors further classify adults as having one of two types of axSpA:
In ankylosing spondylitis (AS) inflammation in the spine leads to changes that are visible on x-ray.
Over time, inflammation can lead to changes in the bones including ankylosis – new bone formation – causing sections of the spine to fuse in a fixed, immobile position. AS can also impact other areas of the body such as the neck, hips, ribs, heels, and other joints.
Not all people with axSpA will have bone changes that are visible on x-rays. When other signs and symptoms of axSpA are present, but spinal changes are not visible on x-ray, the diagnosis is non-radiographic axial spondyloarthritis (nr-axSpA). AS and nr-axSpA are thus part of the same axSpA disease spectrum and present with many of the same symptoms. The main difference is that those with nr-axSpA don’t show bone changes on x-rays, although inflammation can be spotted with the help of MRI. Some people with nr-axSpA progress to developing AS, although many do not.
Peripheral spondyloarthritis (pSpA) is characterized by inflammation and pain in joints and/or tendons primarily located outside the spine. Commonly involved sites include joints in the hands, wrists, elbows, shoulders, knees, ankles, and feet. Inflammation of the tendons can occur in the fingers or toes (dactylitis) or where tendons and ligaments attach to bone (enthesitis). Other organs can also become involved, including the eyes (iritis), gut (inflammatory bowel disease), and skin (psoriasis).
PSpA encompasses a number of distinct, though closely related conditions, including psoriatic arthritis, enteropathic arthritis, reactive arthritis, and undifferentiated arthritis.
Psoriatic arthritis (PsA) frequently causes inflammation, pain, and swelling in the small joints of the hands and feet. Other joints including the wrists, knees, and ankles can also become involved. Most people with PsA will have a skin rash called psoriasis, which causes scaly patches. In most cases the psoriasis will precede the arthritis. Some people will have a “sausage digit” with a toe or finger that swells between the joints and around the joints – this is called dactylitis. A portion of people with PsA also have pain and stiffness in the spine.
In addition to inflammatory back and/or joint pain, inflammation of the intestine, which includes the bowel, is a predominant feature of enteropathic arthritis (EnA). Symptoms may include chronic diarrhea, abdominal pain, weight loss, and/or blood in the stool. The most common types of inflammatory bowel diseases are Crohn’s, ulcerative colitis, and undifferentiated colitis.
In reactive arthritis (ReA) an infection in the intestine or urinary tract usually occurs before inflammation develops in the joints. As such, it is thought to occur as a reaction to an infection. ReA can cause inflammation and pain in the joints, skin, eyes, bladder, genitals, and mucus membranes. Infrequently it can also impact the spine. ReA tends to follow a limited course, with symptoms typically subsiding in three to 12 months. The condition does tend to recur, however, and some people with ReA will develop a chronic form of arthritis.
People with undifferentiated spondyloarthritis (USpA) have symptoms and disease features consistent with spondyloarthritis, but their disease doesn’t fit into another category of SpA. For example, an adult may have iritis, heel pain (enthesitis), and knee swelling, without back pain, psoriasis, a recent infection, or intestinal symptoms. This person’s combination of disease features suggests spondyloarthritis, but may not neatly fit into the categories of ankylosing spondylitis, psoriatic arthritis, reactive arthritis, non-radiographic spondyloarthritis, or enteropathic arthritis.
A note on children with spondyloarthritis: When SpA symptoms begin in childhood, the child is said to have juvenile spondyloarthritis (JSpA). Some children with JSpA will have spinal arthritis as a predominant symptom. These children can be said to fall in the axial spondyloarthritis category. Other children with JSpA will have predominantly peripheral symptoms, with pain and arthritis occurring in joints and tendons outside the spine, such as hips, knees, and ankles. These children can be said to fall in the peripheral spondyloarthritis category.
JSpA can look like any other type of spondyloarthritis. Enthesitis – inflammation where tendons or ligaments meet bone – is often a dominant disease feature.
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