Dish Diffuse Idiopathic Skeletal Hyperostosis Radiology

Idiopathic skeletal hyperostosis, commonly known as DISH, is a systemic condition characterized by the calcification and ossification of ligaments, primarily where they attach to the spine. This condition can also affect other areas of the body, leading to stiffness, pain, and reduced range of motion. Radiography plays a crucial role in the diagnosis and management of DISH, enabling clinicians to visualize the characteristic features of the disease and differentiate it from other musculoskeletal disorders. This article delves into the radiological aspects of DISH, covering its diagnostic criteria, imaging modalities, differential diagnosis, and clinical significance.

Understanding DISH: An Overview

DISH, or diffuse idiopathic skeletal hyperostosis, is a non-inflammatory systemic condition that primarily affects the spine but can also involve peripheral joints. The hallmark of DISH is the flowing calcification and ossification along the anterolateral aspect of the vertebral bodies, typically spanning at least four contiguous vertebrae. This ossification occurs at the entheses, which are the sites where ligaments and tendons attach to bone.

The exact etiology of DISH remains unclear, but several factors are believed to contribute to its development. These include:

• Genetic Predisposition: There is evidence to suggest that genetic factors play a role in the susceptibility to DISH.
• Metabolic Factors: Conditions such as diabetes mellitus, obesity, and hyperuricemia have been associated with an increased risk of DISH.
• Hormonal Influences: Hormonal imbalances and growth factors may also contribute to the development of DISH.
• Mechanical Stress: Repetitive stress and strain on the spine may promote the ossification of ligaments.

The prevalence of DISH increases with age, with most cases diagnosed in individuals over the age of 50. Men are more commonly affected than women. While DISH is often asymptomatic, some individuals may experience symptoms such as stiffness, pain, and reduced range of motion, particularly in the back and neck.

The Role of Radiology in Diagnosing DISH

Radiology is essential for diagnosing DISH and distinguishing it from other spinal disorders. Various imaging modalities can be used to visualize the characteristic features of DISH, including:

Conventional Radiography

Conventional radiography, or X-rays, is the primary imaging modality used to diagnose DISH. It is readily available, relatively inexpensive, and provides valuable information about the bony structures of the spine. The diagnostic criteria for DISH, as defined by Resnick and Niwayama, include:

1. Flowing Calcification and Ossification: The presence of continuous calcification and ossification along the anterolateral aspect of at least four contiguous vertebral bodies. This is the hallmark feature of DISH.
2. Preservation of Disc Height: The absence of significant disc space narrowing, osteophyte formation, or vacuum phenomenon. This helps differentiate DISH from degenerative disc disease.
3. Absence of Apophyseal Joint Ankylosis: The absence of fusion of the facet joints. This helps differentiate DISH from ankylosing spondylitis.

On radiographs, DISH appears as smooth, flowing ossification that bridges the vertebral bodies. The anterior longitudinal ligament is typically the site of ossification, resulting in a characteristic "candle wax" appearance. The ossification may be continuous or interrupted and can vary in thickness.

Computed Tomography (CT)

Computed tomography (CT) provides detailed cross-sectional images of the spine, allowing for a more precise evaluation of the bony structures and surrounding tissues. CT is particularly useful in assessing the extent and severity of ossification in DISH. It can also help identify complications such as spinal stenosis or compression of neural structures.

In DISH, CT scans reveal the flowing ossification along the vertebral bodies, similar to what is seen on radiographs. However, CT provides better visualization of the ossification's density and distribution. It can also help differentiate DISH from other conditions such as ankylosing spondylitis, which may have similar radiographic features.

Magnetic Resonance Imaging (MRI)

Magnetic resonance imaging (MRI) is a valuable imaging modality for evaluating soft tissues and detecting inflammatory changes in the spine. While MRI is not typically used to diagnose DISH, it can be helpful in assessing the presence of associated complications such as spinal cord compression or inflammation of the entheses.

In DISH, MRI may show edema or inflammation in the ligaments and tendons surrounding the spine. It can also help identify areas of spinal cord compression caused by the ossification of the vertebral bodies. Additionally, MRI can be used to rule out other conditions that may mimic DISH, such as infectious spondylitis or metastatic disease.

Diagnostic Criteria for DISH

The diagnostic criteria for DISH, as proposed by Resnick and Niwayama, are widely used in clinical practice and research. These criteria are based on radiographic findings and include the following:

• Flowing Calcification and Ossification: The presence of continuous calcification and ossification along the anterolateral aspect of at least four contiguous vertebral bodies. This is the most important criterion for diagnosing DISH. The ossification should be well-defined and extend across multiple vertebral levels.
• Preservation of Disc Height: The absence of significant disc space narrowing, osteophyte formation, or vacuum phenomenon. This helps differentiate DISH from degenerative disc disease. The disc spaces should be relatively well-preserved, with minimal signs of degeneration.
• Absence of Apophyseal Joint Ankylosis: The absence of fusion of the facet joints. This helps differentiate DISH from ankylosing spondylitis. The facet joints should be clearly visible and not fused together.

In addition to these criteria, other radiographic features may be present in DISH, such as:

• Enthesophytes: The presence of bony spurs at the sites of ligament and tendon attachments. These enthesophytes can occur throughout the spine and peripheral joints.
• Heterotopic Ossification: The formation of bone in soft tissues, such as muscles or ligaments. This can occur in various locations, including the hips, knees, and shoulders.

Differential Diagnosis of DISH

DISH must be differentiated from other spinal disorders that may have similar radiographic features. These include:

• Ankylosing Spondylitis: Ankylosing spondylitis is a chronic inflammatory disorder that primarily affects the spine. It is characterized by inflammation of the sacroiliac joints and spine, leading to fusion of the vertebrae. Unlike DISH, ankylosing spondylitis typically involves the sacroiliac joints and facet joints. Radiographic features of ankylosing spondylitis include sacroiliitis, squaring of the vertebral bodies, syndesmophytes (vertical bony bridges between vertebrae), and fusion of the facet joints.
• Degenerative Disc Disease: Degenerative disc disease is a common condition that results from the breakdown of the intervertebral discs. It is characterized by disc space narrowing, osteophyte formation, and endplate sclerosis. Unlike DISH, degenerative disc disease typically involves the disc spaces and endplates. Radiographic features of degenerative disc disease include disc space narrowing, osteophytes, endplate sclerosis, and vacuum phenomenon.
• Spinal Stenosis: Spinal stenosis is a narrowing of the spinal canal, which can compress the spinal cord and nerve roots. It can be caused by various factors, including degenerative changes, herniated discs, and bone spurs. While DISH can contribute to spinal stenosis, it is not the sole cause. Radiographic features of spinal stenosis include narrowing of the spinal canal, thickening of the ligamentum flavum, and compression of the spinal cord and nerve roots.
• Calcium Pyrophosphate Deposition Disease (CPPD): CPPD is a condition characterized by the deposition of calcium pyrophosphate crystals in the joints and surrounding tissues. It can affect the spine and mimic the radiographic features of DISH. However, CPPD typically involves the disc spaces and facet joints, while DISH primarily affects the anterior aspect of the vertebral bodies.
• Fluorosis: Fluorosis is a condition caused by excessive fluoride intake, which can lead to skeletal abnormalities. It is characterized by increased bone density, periosteal thickening, and calcification of ligaments. Fluorosis can mimic the radiographic features of DISH, but it typically involves the entire skeleton, while DISH primarily affects the spine.

Clinical Significance of DISH

While DISH is often asymptomatic, it can cause various symptoms and complications, including:

• Stiffness and Pain: DISH can cause stiffness and pain in the back, neck, and other affected joints. The stiffness is typically worse in the morning and improves with activity. The pain can range from mild to severe and may be exacerbated by movement.
• Reduced Range of Motion: DISH can limit the range of motion in the spine and other affected joints. This can make it difficult to perform daily activities such as bending, twisting, and reaching.
• Dysphagia: DISH in the cervical spine can cause dysphagia, or difficulty swallowing. This is due to the compression of the esophagus by the ossification of the vertebral bodies.
• Airway Obstruction: In rare cases, DISH in the cervical spine can cause airway obstruction due to compression of the trachea.
• Spinal Cord Compression: DISH can contribute to spinal cord compression, which can cause neurological symptoms such as weakness, numbness, and tingling in the arms and legs.
• Increased Risk of Fractures: The ossification of the ligaments in DISH can make the spine more rigid and prone to fractures, particularly after trauma.

The management of DISH typically involves conservative measures such as pain management, physical therapy, and lifestyle modifications. In severe cases, surgery may be necessary to relieve spinal cord compression or improve range of motion.

Advanced Imaging Techniques

While conventional radiography remains the cornerstone of DISH diagnosis, advanced imaging techniques offer enhanced visualization and diagnostic capabilities.

Magnetic Resonance Neurography (MRN)

MRN is a specialized MRI technique focusing on visualizing peripheral nerves. In the context of DISH, MRN can be employed to assess nerve involvement, especially in cases where peripheral enthesophytes impinge on neural structures. This detailed imaging helps in planning targeted interventions and managing pain associated with nerve compression.

Dual-Energy X-ray Absorptiometry (DEXA)

DEXA scans are primarily used to measure bone mineral density but can also provide insights into the overall bone health of patients with DISH. Although DISH is characterized by hyperostosis, DEXA can help identify coexisting conditions like osteoporosis, which can influence fracture risk and treatment strategies.

Ultrasound

Musculoskeletal ultrasound is a dynamic imaging modality that allows for real-time assessment of soft tissues and joint structures. In DISH, ultrasound can be used to evaluate peripheral enthesophytes, assess inflammation, and guide injections for pain management. Its accessibility and lack of radiation make it a valuable tool in monitoring disease progression and treatment response.

Radiological Reporting in DISH

Accurate and comprehensive radiological reporting is crucial for the effective management of DISH. A well-structured report should include the following elements:

1. Patient Demographics and Clinical History: Start with relevant patient information, including age, gender, and any pertinent clinical history, such as symptoms, duration of symptoms, and previous treatments.

2. Imaging Modality and Technique: Specify the type of imaging performed (e.g., X-ray, CT, MRI) and the technical parameters used.

3. Description of Findings: Provide a detailed description of the radiological findings, including:

   • The presence and extent of flowing calcification and ossification along the vertebral bodies.
   • The number of contiguous vertebral bodies involved.
   • The presence of enthesophytes or heterotopic ossification.
   • The status of the disc spaces and facet joints.
   • Any evidence of spinal stenosis, spinal cord compression, or other complications.

4. Differential Diagnosis: Discuss possible alternative diagnoses and explain why they are less likely given the radiological findings.

5. Conclusion: Summarize the key findings and provide a clear diagnosis or impression.

6. Recommendations: Offer recommendations for further evaluation or management, such as additional imaging, consultation with a specialist, or specific treatment options.

The Future of DISH Radiology

Advancements in imaging technology and artificial intelligence (AI) are poised to transform the radiological assessment of DISH.

Artificial Intelligence (AI)

AI algorithms can be trained to automatically detect and quantify the characteristic features of DISH on radiographs and CT scans. This can improve the efficiency and accuracy of diagnosis, particularly in busy clinical settings. AI can also be used to predict disease progression and identify patients at risk of developing complications.

3D Printing

3D printing technology can be used to create patient-specific models of the spine based on CT or MRI scans. These models can be used for surgical planning, allowing surgeons to visualize the anatomy and practice complex procedures before performing them on the patient.

Molecular Imaging

Molecular imaging techniques, such as positron emission tomography (PET) and single-photon emission computed tomography (SPECT), can be used to visualize metabolic activity and inflammation in the spine. This can help identify early signs of DISH and monitor the response to treatment.

Conclusion

Radiology plays a central role in the diagnosis and management of DISH. Conventional radiography is the primary imaging modality used to diagnose DISH, but CT and MRI can provide additional information about the extent and severity of the disease. The diagnostic criteria for DISH, as defined by Resnick and Niwayama, are based on radiographic findings and include flowing calcification and ossification along the vertebral bodies, preservation of disc height, and absence of apophyseal joint ankylosis. DISH must be differentiated from other spinal disorders such as ankylosing spondylitis, degenerative disc disease, and spinal stenosis. While DISH is often asymptomatic, it can cause stiffness, pain, reduced range of motion, and other complications. The management of DISH typically involves conservative measures, but surgery may be necessary in severe cases. Advancements in imaging technology and artificial intelligence are poised to transform the radiological assessment of DISH, improving the accuracy and efficiency of diagnosis and management. By understanding the radiological aspects of DISH, clinicians can provide optimal care for patients with this condition.