Diffuse idiopathic skeletal hyperostosis (DISH) is a fairly common form of arthritis. Also called Forestier’s disease or ankylosing hyperostosis, DISH primarily affects the thoracic spine (upper back area). Ankylosing spondylitis (AS), on the other hand, is a form of spondyloarthritis that primarily impacts the lumbar (lower) spine.
Unlike AS, DISH is not a form of inflammatory arthritis. However, DISH is sometimes misdiagnosed as AS because the conditions share similar signs and symptoms. Despite these similarities, DISH and AS are very different health conditions.
The usual age of onset for AS is between 15 and 30 years old; DISH usually develops after 50. In the United States, DISH affects about 4 percent of women and 19 percent of men over the age of 50, while an estimated 1 percent of the general population is living with ankylosing spondylitis. The prevalence of AS is increasing in women, while DISH remains twice as likely to affect men.
Here’s what to know about DISH, AS, and differentiating between the two.
DISH is a type of osteoarthritis that results in a process known as calcification (abnormal calcium buildup). Calcification in DISH affects the ligaments and connections between the vertebrae called the entheses (the connective tissue where the tendons and ligaments attach to the vertebrae).
The buildup of calcium causes bone spurs (outgrowths of bone) to develop along the edges of the vertebrae. This bone formation (known as ossification) typically develops in the upper part of the spine (thoracic spine) and the neck (cervical spine).
Severe ossification (bone growth) of the ligament in the front of the spine (anterior longitudinal ligament) can lead to dysphagia, or difficulty swallowing. Ossification of the ligament in the back of the spine (the posterior longitudinal ligament), on the other hand, can cause cervical myelopathy (clumsy hands and gait).
Spine stiffness and pain are typical symptoms of DISH. These symptoms commonly affect other areas, too, like the elbows, knees, heels, and shoulders. A person with DISH may also experience morning stiffness and a reduced range of motion, particularly affecting the back and neck.
Ankylosing spondylitis also affects the entheses of the spine. When AS inflammation erodes the connective tissues and bone, the immune system scrambles to repair it with new bone formation, called syndesmophytes (a type of bony growth in the ligaments). These growths can lead to fusion of the spine, called ankylosis.
AS usually causes pain, inflammation, and stiffness in the lumbar spine and in the sacroiliac joints (where the base of the spine meets the pelvis). In some cases, AS affects the spine in the neck and upper back, also causing cervical myelopathy. About half of people living with AS will also develop osteoporosis — a condition in which the bones become weakened, porous, and more prone to spinal fractures.
AS pain, inflammation, and reduced range of motion can affect multiple areas of the body, including the hips, shoulders, and some peripheral joints (joints that are farther from the center of the body). In some cases, AS can also cause signs and symptoms in the gastrointestinal tract, rib cage, jaw, eyes, or the heart and lungs. Morning stiffness is another typical symptom of living with ankylosing spondylitis.
More often than not, a person will start to experience ankylosing spondylitis symptoms before the disease becomes visible to doctors on imaging tests such as X-rays. DISH, however, is much more likely to be asymptomatic in its early stages. DISH is often discovered by chance when radiograph images taken for other reasons show abnormalities.
When both diseases are in advanced symptomatic phases, however, they have much in common: AS and DISH are both forms of arthritis that can produce new bone formation in the spine. Both conditions can involve the tendons, ligaments, and entheses. Both conditions can also cause back pain, a reduced range of motion, myelopathies, and morning stiffness. Over time, these conditions can both lead to a stooped posture.
So, how do doctors tell DISH and AS apart?
A person’s family and personal medical histories can be helpful in the differential diagnosis of DISH and AS. The cause of DISH is still unknown, but advanced age and obesity are risk factors. A diagnosis of DISH is also more likely when an individual has a medical history of metabolic disorders such as type 2 diabetes or metabolic syndrome. The use of certain acne medications, such as Claravis (isotretinoin), is also known to increase the risk of developing DISH.
The exact cause of AS is also uncertain, but it is known to be an autoimmune disease. Autoimmune diseases involve an overactive response from the immune system, causing the immune system to attack healthy tissues by mistake. Autoimmune diseases may have genetic predispositions. The gene considered a risk factor for ankylosing spondylitis is HLA-B27, though it’s possible to have the HLA-B27 gene and never develop AS. Likewise, you can have AS without the HLA-B27 gene. Still, testing for the HLA-B27 gene can be a useful diagnostic tool.
Physical examinations, radiographic imaging, and blood tests are all part of the differential diagnosis of AS and DISH. A rheumatologist will typically perform a physical exam to check for decreased range of motion and other abnormalities. They will usually conduct blood tests to look for inflammatory markers in the blood to support a diagnosis of AS.
The pelvic and spinal abnormalities seen on radiographs (X-ray images) differ greatly between AS and DISH. New bone formations may show up in similar locations on images of both conditions, but the following criteria suggested by researchers highlight some helpful distinctions:
Thanks to radiographic imaging, DISH and AS can be identified separately, even if a person is living with both conditions.
DISH and AS are chronic diseases that can both lead to disability. The severity of symptoms varies greatly from one person to the next. Early diagnosis and intervention are key to maintaining a relatively normal and active lifestyle with these conditions.
Similar treatments can ease symptoms and slow disease progression for both DISH and AS. You can work with your health care team to determine what treatment or combination of treatments will best manage your condition.
Physical therapy, stretching, and exercise can help preserve range of motion, reduce pain, and improve strength and balance. Occupational therapy and prescribed technical supports, such as a brace, may also help a person with AS or DISH perform everyday tasks.
For both conditions, corticosteroid injections are also helpful for reducing pain in the short term.
There is no one diet recommended for people with DISH or AS. Certain foods can trigger flares in some people, so it is important to make personalized dietary changes as needed. The Mediterranean diet is considered a helpful anti-inflammatory diet for people living with inflammatory arthritis such as AS. Part of managing DISH involves maintaining a healthy weight and blood sugar level through a healthy diet.
Both heat and cold can help alleviate pain, stiffness, and swelling associated with DISH and AS. Heat helps alleviate pain and tension by loosening the muscles around the joints and increasing flexibility and circulation. Cold, on the other hand, helps reduce inflammation, swelling, and pain.
For hot therapy, the Cleveland Clinic recommends showering or soaking in a warm bath for 20 minutes or using a heating pad. Applying a moist dishcloth warmed in the microwave for 20 seconds can work in the same way.
Cold therapy can be applied for 20 minutes at a time using a gel-filled cold pack, frozen peas, or a baggie filled with ice.
Meditation, mindfulness, and other stress management practices may help keep stress levels low and help prevent symptoms from worsening during flares.
Surgery is not always needed for AS or DISH. Surgery may be necessary if DISH causes problems with the structure of the spine, such as by forming bone spurs that press on the esophagus and cause difficulty swallowing or breathing. Your health care team can advise you on whether surgery is the right option for you.
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