What is Diffuse Idiopathic Skeletal Hyperostosis?
Diffuse idiopathic skeletal hyperostosis (DISH) is a condition that causes abnormal bone growth patterns. It predominantly affects the spine, causing back pain and stiffness. The term “DISH” was first used to describe this condition in 1975, and it is now the most common term used in medical literature. It was initially called “senile ankylosing hyperostosis” in 1950, when it was first described in detail in medical studies.
DISH causes bone to grow along the front of at least three or four connected vertebrae in the spine. This growth is often described as “flowing”. Although it’s less common, DISH can also cause bone growth at the joints of the shoulder, elbow, knee, or heel. In the spine, DISH most often affects the right side of the thoracic spine, which is the mid-to-upper part of the spine.
The exact cause of DISH is not well understood. Some risk factors have been identified, including gout, high cholesterol, and diabetes. HLA-B8, a marker found in both DISH and diabetes, is commonly seen. This suggests that there is a high occurrence of diabetes, high uric acid, and high cholesterol in people with DISH. However, no link has been found between DISH and HLA-B27, unlike in other similar conditions.
What Causes Diffuse Idiopathic Skeletal Hyperostosis?
Recent research has shown a strong link between a condition known as DISH and metabolic disorders like diabetes, obesity, high insulin levels, abnormal cholesterol levels, and high levels of uric acid. While these relationships have been discussed in medical studies, it’s still unclear how these result in the bone growth patterns seen in DISH.
Some researchers have tried to explain possible causes, such as physical stress and strain, exposure to harmful substances, and genetic factors. Another potential factor being investigated is the growth of new blood vessels, which could theoretically create a plausible link between the various ways DISH appears in patients. For instance, in patients with metabolic syndrome, rates of DISH and hardening of the arteries in the neck are higher.
Furthermore, a higher rate of hardening of the aortic valve has been identified as a risk factor for heart problems in patients with DISH.
Risk Factors and Frequency for Diffuse Idiopathic Skeletal Hyperostosis
DISH, or Diffuse Idiopathic Skeletal Hyperostosis, is a condition that doesn’t get mentioned a lot. But it is worth knowing that it doesn’t usually affect people younger than 50. About 6 to 12% of the general population has it. For people over 50, it is found in about 25% of males and 15% of females. As people grow older, the prevalence rates increase, reaching 28% and 26% for men and women over 80, respectively.
Studies suggest that the condition starts to develop between the ages of 30 and 50 but shows up clinically at a later age. In fact, about one in four people who died and were autopsied showed signs of DISH, with an average age of 65. Population studies found rates between 2.5% and 28%, increasing with age and more common in men than in women. Also, DISH seems to be more common in White populations compared to Black, Asian, or Native American populations.
A noteworthy piece of research from Japan in 2016 showed different prevalence rates when diagnosed via CT scans and radiograph imaging. The occurrence of DISH in Japan’s general population was reported to be 17.6% and 27.2% for radiographs and CT imaging, respectively.
Signs and Symptoms of Diffuse Idiopathic Skeletal Hyperostosis
DISH, or Diffuse idiopathic skeletal hyperostosis, is a disease that is often found unintentionally since it tends not to have visible symptoms. However, nerve damage or excessive bone growth can cause discomfort and pain.
The traditional method to diagnose DISH involves checking for these main signs:
- There should be a continuous growth of bone that includes at least four vertebrae in the spine
- The disc height between the vertebrae in question remains normal, differentiating DISH from degenerative spondylosis, another spinal disorder
- There shouldn’t be any sign of ankylosis at the facet-joint interface, or any indications of sacroiliac joint erosion, sclerosis, or fusion, all of which sets DISH apart from ankylosing spondylitis (AS)
However, this definition has been challenged, asking whether it’s only applicable to advanced stages of the condition. Some suggest lowering the bar for spinal involvement to two vertebrae and also including the presence of peripheral enthesopathies, which is disease at the site where ligaments and tendons attach to bone.
Experts are also debating other criteria used in the diagnosis. A recent Delphi exercise pointed to robust bone formation at specific locations and enlarged bony bridges in the C-spine, T-spine, or L-spine as potential markers on which most could agree.
Differentiating between DISH and AS often confuses healthcare providers. DISH, compared to AS, usually appears in older age, without signs of sacroiliac joint erosions or apophyseal joint obliteration. DISH also tends to be associated with excessive bone formation of the anterior longitudinal ligament, absent enthesopathies with erosions, and no link to the HLA-B27 gene.
Though DISH can present with significant changes in X-rays or other advanced images, the clinical symptoms are usually mild. In fact, DISH is often discovered by chance in patients showing no symptoms. Classic signs, if present, may be seen in an older patient with increasing back pain and stiffness. Swelling of soft tissues due to excessive bone growth in the neck can cause difficulty swallowing, hoarseness, sleep apnea, and problematic intubation. Trauma in such cases could lead to fractures due to fused osseous elements of the spine, increasing the need for careful inspection and imaging studies.
Other distinctive features of DISH can be seen in peripheral joints. There may be involvement in joints usually spared by primary osteoarthritis, like the hip and knee. The foot and ankle, involved in up to 70% of cases, might show signs similar to heel spurs, Achilles tendinitis, and plantar fasciitis. There may also be an increase in hypertrophic changes compared to primary osteoarthritis, prominent enthesopathies near peripheral joints, and calcification and ossification at attachment sites other than the joints.
Patients may also show thickening of the bone (hyperostosis) and inflammation of the tendon (tendonitis). Enthesophytes, or abnormal bony projections, might be seen in the pelvis along the iliac wing and ischial tuberosity, while periarticular hyperostosis and tendon ossifications can be detected in the hips, knees, shoulders, elbows, hands, and wrists.
Testing for Diffuse Idiopathic Skeletal Hyperostosis
In simple terms, various lab tests often show regular results in patients with DISH (Diffuse Idiopathic Skeletal Hyperostosis). X-ray tests, or radiographic evaluation, can show signs of DISH in the patient’s spine, which might look like flowing candle wax. This is different from what we call “bamboo spine,” another sign found in a specific condition called ankylosing spondylitis (AS).
X-ray tests of the spine can also show increased density and normal joint and disc spaces, which helps doctors tell DISH apart from AS, which usually comes with lower bone density and joint changes. This difference in bone density between DISH and AS can help to predict the risk of fractures. For instance, the literature mentions that patients with weakness in their bones (osteoporosis) can experience fractures even with minimal force, such as lying in bed. Similarly, there have been cases of fractures in patients with DISH after routine surgery.
Since DISH most commonly affects the thoracic spine (upper and middle back), doctors should be quick to order chest or spinal X-rays when a patient has complaints of neck or back pain or stiffness. Early diagnosis of DISH using these images can help to avoid unnecessary medical processes and surgery. A Technetium bone scan, another imaging technique, may show increased uptake in DISH-affected areas, though it is generally not very useful for non-traumatic situations. Doctors should also check images of the pelvic and lumbar spine (lower back), as any condition affecting the sacroiliac (lower back and hip) region can help point to other possible conditions.
Patients with DISH are known to have an increased risk of fractures and instability due to minor injuries. These fractures are often overlooked initially, leading to nerve damage and delays in treatment. Advanced imaging techniques, like CT scans, MRI, or CT myelogram, should be used for a thorough evaluation of these patients. If the patients complain of problems outside the spine, simple X-ray images can help with their evaluation.
Treatment Options for Diffuse Idiopathic Skeletal Hyperostosis
For most people suffering only from back pain, the primary treatments usually include changing certain activities, physical therapy, using supportive braces, anti-inflammatory drugs, and bone-strengthening medication.
Surgery to relieve pressure and stabilize the spine might be needed for specific outcomes of the condition. These could include a spinal fracture, neck-related nerve dysfunction, narrowing of the spine in the lower back, neurological impairments, infection, or pain due to a misshapen spine.
What else can Diffuse Idiopathic Skeletal Hyperostosis be?
Doctors examining patients with back pain, stiffness and spondylophytosis may also consider other conditions that can cause similar symptoms. These could include:
- Ankylosing spondylitis (a type of arthritis that affects the spine)
- Spondylosis deformans (a spine condition usually related to ageing)
- Seronegative spondyloarthropathies (a group of diseases that cause arthritis)
- Charcot spine (a condition that leads to the weakening of the bones in the spine)
- Acromegaly (a hormonal disorder that develops when the pituitary gland produces too much growth hormone)
- Psoriasis (a skin disorder)
- Reactive arthritis (a condition that causes inflammation in various places in the body)
- Pseudogout (a type of arthritis)
- Hypoparathyroidism (where the body doesn’t produce enough parathyroid hormone)
It’s crucial for your doctor to evaluate all these conditions and carry out relevant tests to diagnose your condition correctly.
Possible Complications When Diagnosed with Diffuse Idiopathic Skeletal Hyperostosis
People with DISH, a condition affecting the spine, are more likely to have unstable spine fractures due to calcification in the ligaments and increased abnormal forces that cause the spine vertebrae to fuse. Because of these factors, a longer instrument is often needed for fixation during surgery. A study by Meyer showed that there is a 15% death rate in older patients with DISH who have neck fractures and undergo surgical treatment. This is significantly lower than the 67% death rate in patients who receive conservative, non-surgical treatment. This further emphasizes the importance of quick recognition, assessment, and treatment in DISH patients who have suffered a trauma.
Heterotopic ossification (HO), a common issue where bone grows in places it shouldn’t, often happens after total hip replacement surgery in patients with DISH. The rates of this happening range from 30% to 56%. In contrast, patients without DISH only have a 10% to 22% rate of experiencing HO after hip surgery. However, Fahrer et al. reported that the pain and functional limitations associated with HO are low in patients with DISH who have had a hip replacement, and recommended against any preventative measures against HO in these patients.
Preventing Diffuse Idiopathic Skeletal Hyperostosis
Patients and their families need to be made aware that they may be more prone to serious, and potentially life-threatening, complications. This can happen even in situations where there is minor physical trauma or after undergoing routine surgeries. Therefore, it’s essential that patients and their families are well-informed about these potential risks.
