Ankylosing spondylitis

Definitions & Key takeaways

Ankylosing spondylitis (AS) is a form of arthritis that primarily affects the spine. This chronic condition can lead to fusion of the vertebrae, resulting in a rigid spine. AS can also affect the sacroiliac joints, peripheral joints, and digits, and in severe cases, it can lead to disability. Some of the symptoms seen in AS include back pain, postural abnormalities, buttock pain, and pain in the peripheral joints such as the hips, knees, and ankles.

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Introduction0:00–0:46

Ankylosing spondylitis can be broken down - Ankylosing means stiffening, spondylo- refers to the vertebra, and -itis refers to inflammation.
So ankylosing spondylitis is a chronic inflammatory disease that affects the vertebral joints and makes the spine really stiff, but can also cause inflammation in other parts of the body like the eyes and blood vessels.
Ankylosing spondylitis, also called Bechterew disease, is part of a group of diseases called seronegative spondyloarthropathies.
Spondyloarthropathies are all autoimmune diseases that affect the joints, and they’re seronegative, which refers to the fact that rheumatoid factor, which is an autoantibody, is not found in the blood.

Physiology0:46–0:46

Physiology0:46–2:16

Alright, so in the healthy adult, the vertebral column is made up of 33 bones. From top to bottom, the first seven bones are the cervical vertebrae, the next twelve are the thoracic vertebrae and the next five, are the lumbar vertebrae.
Below that is a bone called the sacrum, which is attached to the pelvic bone on either side, called the ilium, and where they meet is the sacroiliac joint.
Below the sacrum is a tiny bone called the coccyx or tailbone. There are two types of joints between the vertebra.
Between each of the vertebral bodies is an intervertebral disc which is made of type I and type II collagen and has two parts, the annulus fibrosis, an outer fibrous ring, and the nucleus pulposus, an inner jelly-like substance.
This disc forms a joint between each vertebra, and it allows slight movement and acts as a shock absorber. In addition to the intervertebral discs, each vertebra has joints called facet joints with the vertebra above and the vertebra below, one on each side.
These joints are synovial, meaning they have a joint capsule and a small amount of synovial fluid in between. When you stretch your back the capsule in these joints stretches too and decreases the pressure in the joint space, which makes any gas suddenly come out of solution, making a cracking sound!
They help guide and limit the range of motion in your spine. In ankylosing spondylitis there’s chronic inflammation of the the intervertebral joints and the facet joints of the spine.

Pathology2:16–5:15

The exact cause of the inflammation is unclear, but it’s thought to be due to an autoimmune process - which is when the immune system attacks its own tissue - in this case the type I and type II collagen in the joints.
But unlike many other autoimmune conditions, no autoantibody has been specifically linked to the disease. Normally, the cells of the immune system are ready to spot and destroy anything foreign that could cause the body harm.
To help with this, most cells in the body have a set of proteins that combine together to form something called a major histocompatibility complex, or MHC, class I molecule that sits on the surface of their cell membrane.
Most individuals with ankylosing spondylitis have the gene HLA-B27, which is a gene that encodes for a specific type of MHC class I molecule.
These surface proteins act kind of like a serving platter, presenting molecules from within the cell for the immune system to continually sample.
A type of T-lymphocyte, called a CD8+ T-cell, also known as a cytotoxic T-cell, uses its T-cell receptors to bind to the antigen presented by the MHC class I molecule.
Normally though the molecule’s just a sample from the cell, and the immune system recognizes it as harmless, and this is known as a self-antigen, and there’s no response.
But when these cells recognise a foreign molecule, they use cytokines to signal other immune cells to migrate to the joint capsule and the joint space that’s under attack, cells like neutrophils.
The neutrophils release cytokines like tumor necrosis factor alpha, or TNF-ɑ and interleukin one, or IL-1, which worsen the inflammation.
Over time, the inflammation destroys the intervertebral joints, the facet joints, and the sacroiliac joints, and fibroblasts replace the destroyed joint with fibrin.
Layers and layers of fibrin form a tough fibrous band around the outside of the joints, which limits their range of motion.
Eventually osteoblasts get activated and a process called ossification will start, which is when the fibrous tissue turns to bone.
In the beginning, small bony outgrowths will form at the joint edges, called syndesmophytes. This makes the part of the spine that’s affected immobile, and sometimes that can be the entire spine.
Other parts of the body can be affected too, like the eye, which can cause anterior uveitis. The aortic valve can sometimes get inflamed and damaged leading to aortic regurgitation.
There can also be inflammation of tendons, like the achilles tendon, called enthesitis. Ankylosing spondylitis is a systemic inflammatory disease, so it can cause symptoms, like weight loss, fevers, and fatigue.

Signs and symptoms5:15–5:40

If ankylosing spondylitis affects the sacroiliac joints it typically causes buttock pain, and if it affects the cervical or thoracic region it can cause neck or back pain and stiffness.
Because the ribs and vertebrae are involved in breathing, stiffness can cause shortness of breath. Ankylosing spondylitis can be diagnosed using MRI, there’s typically erosion and narrowing of the joint spaces early on, and joint fusion later on.

Diagnosis5:40–5:40

Diagnosis5:40–6:09

An X-Ray and CT often show a bamboo spine, which is caused by the ossification of the annulus fibrosus on the outside of a straightened spine, giving it a hollow appearance!
Genetic testing for HLA-B27 can be done to help confirm the diagnosis. Inflammation and pain from ankylosing spondylitis is usually treated with non-steroidal anti-inflammatory drugs like ibuprofen.

Treatment6:09–6:49

The pain can also be relieved by exercise or physical therapy. In more severe case, disease modifying anti-rheumatic drugs, or DMARDs, like sulfasalazine and methotrexate can be helpful.
Newer therapies called biologics can also be useful, because they block the actions of cytokines like tumor necrosis factor alpha and the interleukins.
Surgery can repair damaged hip and knee joints, but spinal surgery is typically considered risky and is rarely performed.
All right, as a quick recap…Ankylosing spondylitis is an autoimmune process, associated with the HLA-B27 gene, which attacks vertebral joints.

Review6:49–7:13

Collagen gets destroyed and replaced by fibrin, and ultimately ossification sets in, forming a “bamboo spine” on Xray or CT.
It can also affect the eyes, aorta, tendons and lungs.