Overview of Types of Spondylitis

Spondyloarthritis, also referred to as spondylitis or SpA, diseases are currently grouped or classified in two main ways:

  • The Traditional SpA Classification System – which recognizes six separate diseases in the system; and,
  • The Newer SpA Classification System – with two broader categories encompassing the full range of SpA.

SAA receives no government funding and relies on the generous donations from individuals to create and maintain the programs and services aimed at improving the futures of the 2.7 million Americans affected by spondylitis.

Traditional SpA Classification System

Ankylosing Spondylitis (AS)

Inflammation in the spine and/or pelvis causes inflammatory back pain. Inflammatory back pain usually starts gradually before the age of 45, tends to improve with activity but not rest, and occurs with stiffness in the morning that lasts at least 30 minutes.

Over time, this inflammation can lead to ankylosis -- new bone formation in the spine -- causing sections of the spine to fuse in a fixed, immobile position. AS can also cause inflammation, pain and stiffness in other areas of the body such as the shoulders, hips, ribs, heels, and other joints.

About Ankylosing Spondylitis

Enteropathic Arthritis (EnA)

Arthritis Associated With Inflammatory Bowel Disease

In addition to inflammatory back and/or joint pain, inflammation of the intestine, which includes the bowel, is a predominant feature of 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.

About Enteropathic Arthritis

Psoriatic Arthritis (PsA)

PsA frequently causes pain and swelling in the small joints of the hands and feet. Most people with PsA have a psoriasis skin rash. Some people have a “sausage digit” with a toe or finger that swells between the joints and around the joints. A portion of people with PsA also have pain and stiffness in the spine.

About Psoriatic Arthritis

Reactive Arthritis (ReA)

An infection in the intestine or urinary tract usually occurs before inflammation in the joints. ReA can cause inflammation and pain in the joints, skin, eyes, bladder, genitals, and mucus membranes. ReA frequently follows a limited course, with symptoms typically subsiding in three to 12 months. The condition does have a tendency to recur, however, and some people with ReA will develop a chronic form of arthritis.

About Reactive Arthritis

Undifferentiated Spondyloarthritis (USpA)

People with 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 she doesn’t neatly fit into the categories of ankylosing spondylitis, psoriatic arthritis, reactive arthritis, juvenile spondyloarthritis, or enteropathic arthritis

About Undifferentiated Spondyloarthritis

Juvenile Spondyloarthritis (JSpA)

Symptoms begin in childhood. JSpA can look like any other type of spondyloarthritis. Enthesitis, inflammation where tendons or ligaments meet bone, is often a dominant disease feature. Children and adolescents with JSpA tend to have more peripheral arthritis than adults with SpA. The arthritis typically involves joints in the lower extremities in an asymmetric fashion.

About Juvenile Spondyloarthritis

Newer SpA Classification System

Axial Spondyloarthritis (AxSpA)

Axial SpA causes inflammation in the spine and/or pelvis that typically brings on inflammatory back pain. AxSpA is a broad category that includes people with and without characteristic damage or fusing of the sacroiliac joints (joints linking the lowest part of the spine to the pelvis) seen on X-ray. 

Doctors classify people as having a certain type of axial spondyloarthritis:

  • Radiographic axSpA, with characteristic damage or fusing seen on X-ray (also called ankylosing spondylitis.) 
  • Non-radiographic axSpA, without characteristic damage or fusing seen on X-ray. (Read more about non-radiographic axSpA, here.

People with ankylosing spondylitis fit into the category of radiographic axSpA. People with reactive arthritis, enteropathic arthritis, undifferentiated spondyloarthritis, and psoriatic arthritis may fit into the category of either radiographic axSpA or nonradiographic axSpA.

The Centers for Disease Control's NHANES study estimates that at least 2.7 million adults in the United States have axial spondyloarthritis.

Peripheral Spondyloarthritis (pSpA)

Peripheral SpA commonly causes inflammation in joints and/or tendons outside the spine or sacroiliac joints. 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 meet with bone (enthesitis). Almost all people with PsA fit into the pSpA category at some point in their disease. People with reactive arthritis, enteropathic arthritis, and undifferentiated arthritis may also fit into this category.

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