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Glossary of Spondyloarthritis

Reviewed by: HU Medical Review Board | Last reviewed: March 2023

When you are diagnosed with a medical condition, you may start to see a lot of medical terms and abbreviations. Not knowing the medical terms for a condition can make it hard to understand what is happening with your care. Learning about your condition is a lot easier when you know these terms.

The following are some common terms you may see when reading about axial spondyloarthritis (axSpA).

Anemia of chronic disease (ACD)

A type of anemia that can occur with axSpA. ACD happens when there are not enough red blood cells produced by the bone marrow. This can lead to fatigue, shortness of breath, and other symptoms.1


Abnormal stiffness or fusion of a joint.2

Ankylosing spondylitis (AS)

A form of arthritis that mostly affects the spine. AS also can cause pain and stiffness in other joints, such as the hips, knees, and shoulders. The symptoms of AS are often mild at first, but they can worsen over time.3

AS is also called radiographic axSpA (r-axSpA) because the damage it causes can be seen on X-rays.3

Axial spondyloarthritis (axSpA)

Spondyloarthritis is a type of arthritis that affects the joints and the areas where ligaments or tendons attach to bone. AxSpA mostly affects the spine, but it also can affect other joints in the body.3,4

Bamboo spine

This condition occurs when the bones in the spine (vertebrae) grow together (fuse). This results in a stiff, rigid spine resembling the appearance of bamboo on an X-ray. Bamboo spine may result when axSpA has progressed to a severe stage. But this does not always occur.4

Cauda equina syndrome

Cauda equina syndrome is a rare complication that can occur in people with axSpA. It happens when the nerves at the bottom of the spine become compressed. This can cause problems with movement and feeling in the legs, as well as loss of bladder and bowel control.4

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A type of medicine that can be used to treat a wide variety of conditions. These drugs are commonly used to reduce inflammation and swelling. They work by mimicking the effects of hormones produced by the body's adrenal glands. These are also known as glucocorticosteroids or steroids.5


Disease-modifying antirheumatic drugs. These drugs decrease pain and inflammation as well as slow the progression of spondyloarthritis.4

Enteropathic arthritis (EnA)

A type of peripheral spondyloarthritis that commonly occurs with inflammatory bowel disease (IBD).6


The locations where the ligaments and tendons attach to a bone.4


Inflammation of the entheses.4

Extra-articular complications

Problems caused by chronic inflammation in parts of the body that are not the joints. Some sites include the skin, eyes, and gut.7


A condition that causes widespread pain in the body. People with axSpA have a greater risk of developing fibromyalgia.4

Fibrosis of the lungs

A rare complication of AS in which scar tissue forms in the connective tissue between the air sacs in the lung and causes shortness of breath.4


A complication of AS where 2 bones of a joint grow together. This leads to stiffness and lack of mobility in the joint.4


A protein found on the surface of white blood cells that causes inflammation. Experts believe this genetic marker plays a role in causing AS. But not everyone with HLA-B27 develops AS, and some people with AS do not have the HLA-B27 marker.2-4

Inflammatory bowel disease (IBD)

IBD causes inflammation in the digestive tract. The 2 most common types of IBD are Crohn's disease and ulcerative colitis. People with axSpA have an increased risk of developing IBD.4

Juvenile-onset ankylosing spondylitis or juvenile ankylosing spondylitis (JAS)

AS that occurs in children or adolescents before the age of 18.8

Juvenile spondyloarthritis (JSpA)

Arthritis conditions that begin before the age of 16.9


When the spine curves outward, resulting in a hunched or rounded back. This is a possible complication as axSpA progresses.7


Non-steroidal anti-inflammatory drugs. Widely used medications for pain and inflammation. These are often used as a first-line treatment to help relieve the symptoms of axSpA. Many are available over-the-counter (OTC), such as ibuprofen (Advil) and naproxen (Aleve).4


A condition in which the bones are weakened and brittle, and therefore at an increased risk of fracture. AxSpA puts at person at greater risk of developing osteoporosis.10

Peripheral joints

Joints in the arms or legs that may be affected in axSpA, such as the hips or shoulders.4

Peripheral spondyloarthritis (pSpA)

A condition that involves pain and inflammation in joints other than the spine, such as those in the arms, legs, and fingers.4,6


A chronic skin condition that causes raised, red, scaly patches on the skin. These patches may be itchy and painful, and they can crack and bleed. Psoriasis is a common extra-articular complication of AS.4

Psoriatic arthritis

A type of peripheral spondyloarthritis that causes pain, swelling, and inflammation in the joints and tendons.6

Radiographic evidence

Signs of axSpA that are visible on imaging, such as X-rays or MRI tests.3

Reactive arthritis

A type of peripheral spondyloarthritis that can result from an infection in another part of the body.4

Sacroiliac (SI) joints

The joints located between the bottom of the spine (the sacrum) and the ilium of the pelvis. These are often the first joints to have symptoms from AS.4


Inflammation of the spine.3,4


An umbrella term that refers to several different arthritis conditions that cause joint inflammation.4


A narrowing of the spinal column that can cause pain or nerve damage. This is a possible complication of AS and axSpA.11


Calcification of the spinal ligaments. These often occur in axSpA.12

TNF inhibitors

Tumor necrosis factor inhibitor drugs, a type of DMARD. These are biologic drugs that block a certain protein that causes too much inflammation in people with AS and axSpA.4

Undifferentiated spondyloarthritis

The condition that is diagnosed when a person does not meet the exact criteria for another type of spondyloarthritis.6


Inflammation that occurs in the middle layer of the eye (uvea). Uveitis causes redness, pain, sensitivity to light, blurry vision, excessive tears, and visual loss. It is a possible complication in people with axSpA or AS.4