Diffuse idiopathic skeletal hyperostosis (DISH) and ankylosing spondylitis (AS) are types of arthritis. They affect tough bands of tissue called ligaments in the spine. In DISH, ligaments harden into bony growths called spurs where they attach to your spine. In AS, inflammation in the ligaments and joints causes stiffness in the spine.
Although the symptoms of DISH and AS might seem similar, there are a few key differences to help your doctor tell which condition you have.
What Causes DISH and Ankylosing Spondylitis?
In DISH, calcium salts build up in the ligaments and tendons around the spine. Calcium makes the bones calcify, or get harder, and grow too much. Doctors don't know exactly why this happens. The cause might be a combination of genes, exposures in the environment, or something else.
Genes and environmental exposures probably trigger AS, too. People who have a gene called human leukocyte antigen (HLA)-B27 are at higher risk. HLAs help your immune system tell your own cells apart from germs and other foreign substances in your body. But experts aren’t yet sure why the gene makes you more likely to get AS.
Who Gets DISH and Ankylosing Spondylitis?
Between 6% and 12% of people have DISH. The condition is most common in men over age 50. As many as 1 in 4 men over 50 have DISH, although they don't all show symptoms.
Your risk for DISH may be higher if you also:
- Have diabetes
- Are very overweight
- Have acromegaly, a disorder caused by too much growth hormone
- Take acne medicines called retinoids
AS is less common, affecting about 1% of people overall. Around 5% of people with the HLA-B27 gene change have this condition. Like DISH, AS is more common in men, but it starts earlier in life — between your teens and 30s.
Can You Have DISH and Ankylosing Spondylitis at the Same Time?
DISH and AS are different diseases and usually don't affect the same person. In fact, the criteria doctors use to diagnose DISH rule out AS, and vice versa. Yet there have been a small number of cases reported in studies where people had both DISH and AS.
How Are DISH and Ankylosing Spondylitis Symptoms Different?
Back pain, stiffness, and less motion in the affected joints are the main symptoms of AS. These can be symptoms of DISH too. But most people with DISH don't have any symptoms. Doctors often find DISH accidentally when they do an X-ray for another reason.
DISH pain is in the upper back, while AS pain is in the lower back. AS pain and stiffness also tend to get better with movement or exercise.
You might also feel pain from DISH in places like your shoulders, elbows, knees, or heels. Bone spurs that press on nerves of the spine can cause numbness or weakness in the legs. Bony growths in the neck could cause trouble swallowing or a hoarse voice.
AS pain also affects areas outside of the back, like the ribs, shoulders, knees, hips, or feet. And it causes more widespread symptoms like:
- Weight loss
- Skin rashes
- Belly pain
- Vision changes
How Do Doctors Tell DISH and Ankylosing Spondylitis Apart?
DISH and AS can be somewhat tricky to diagnose. If you still have questions or you don't feel like you got the right diagnosis, it's OK to see another doctor for a second opinion.
Your doctor will start by asking about your symptoms and medical history. You're more likely to have DISH if you:
- Are over 50
- Have reduced movement or a curve in your spine
- Have trouble swallowing or a hoarse voice
- Also have diabetes or obesity
It's more likely to be AS if you:
- Are in your teens, 20s, or 30s
- Have a family history of AS
- Also have psoriasis, inflammatory bowel disease (IBD), or eye inflammation called uveitis
- Have trouble standing up straight
A few tests can confirm which of the two conditions you have.
Blood tests. In AS, blood tests may be positive for the HLA-B27 gene or C-reactive protein erythrocyte sedimentation rate (ESR), which are markers of inflammation.
Imaging tests. These tests take pictures of the inside of your body to help your doctor look for changes to the bones and joints of your spine.
- An X-ray uses beams of energy to make pictures of your bones.
- Magnetic resonance imaging, or an MRI, uses radio waves and magnets to take detailed pictures of your spine.
- Computed tomography, or a CT scan, uses a combination of computers and X-rays to take very detailed pictures of your organs and tissues.
If you have AS, imaging tests could show:
- Narrowing and stiffening in the sacroiliac joints where your spine connects to your pelvis, called sacroiliitis
- Bony growths or other changes in your spine
- Bamboo spine, where your spine has fused into one long bone
- Inflammation in the places where ligaments connect with bones
If you have DISH, imaging tests might show:
- Hardening of the ligament that runs down the front of your spine
- A bony bridge between the vertebrae
- Thickening of bones in your hands, elbows, knees, and the front of your thighs
No symptoms and no signs of sacroiliitis on an X-ray will point your doctor to a DISH diagnosis.
What Treatments Work for DISH and Ankylosing Spondylitis?
AS and DISH aren't curable, but treatments can help manage symptoms and complications. Both conditions raise your risk for fractures. That’s because a stiff spine is more likely to break if you injure it.
Some of the same treatments work for both AS and DISH, including:
Physical therapy and exercise. Movement is important to strengthen the muscles that support your spine and keep your joints flexible.
Pain relievers and muscle relaxants. Nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen and naproxen relieve pain and bring down swelling. Muscle relaxants calm muscle spasms.
Steroid injections. Corticosteroids injected into the affected joints offer short-term relief from pain and inflammation.
Surgery. This isn't a common treatment, but surgery may be an option if you have more severe symptoms that don't get better with physical therapy and medicine. In DISH, surgery removes any extra bone that presses on nerves or makes it hard for you to breathe. Surgery for AS replaces damaged joints or removes parts of the thickened bone.
Here are a few other ways to treat DISH:
- Lose weight and lower your blood sugar levels.
- Apply heat from a moist compress or heating pad to sore areas.
- Wear special shoe inserts called orthotics if you have bone spurs in your heels.
Disease-modifying antirheumatic drugs (DMARDs) are another treatment for AS. These medicines bring down inflammation in your body.
Examples of DMARDs are:
- Interleukin-17 inhibitors: ixekizumab (Taltz) and secukinumab (Cosentyx)
- Interleukin 12/23 inhibitor: ustekinumab (Stelara)
- JAK inhibitors: tofacitinib (Xeljanz and Xeljanz XR) and upadacitinib (Rinvoq)
- Methotrexate (Rheumatrex, Trexall)
- Sulfasalazine (Azulfidine)
- Tumor necrosis factor (TNF) inhibitors like adalimumab (Humira), certolizumab pegol (Cimzia), etanercept (Enbrel), infliximab (Remicade), and golimumab (Simponi)