Diffuse Idiopathic Skeletal Hyperostosis (DISH) and Ankylosing Spondylitis (AS) are chronic conditions that primarily affect the spine, leading to stiffness and reduced mobility. Both can cause significant discomfort and impact daily life, often leading to confusion due to their shared presentation of spinal issues. This article aims to clarify the distinctions between these two conditions, exploring their unique characteristics, diagnostic approaches, and management strategies.
Overview of DISH and Ankylosing Spondylitis
Diffuse Idiopathic Skeletal Hyperostosis (DISH) involves the hardening of ligaments and tendons along the spine due to ossification, a process of new bone growth often described as “flowing” bone formation. While it commonly affects the thoracic spine, DISH can also lead to bone spurs in other areas like the hips, knees, shoulders, and heels.
Ankylosing Spondylitis (AS), in contrast, is a chronic inflammatory disease that mainly targets the spine and sacroiliac joints. This inflammation can lead to the formation of new bone, which may cause sections of the spine to fuse together, resulting in a “bamboo spine” appearance. AS typically begins in the sacroiliac joints and lumbar spine, progressing upwards along the spinal column.
Distinct Clinical Features
DISH often presents with morning stiffness that improves with activity and a reduced range of motion in affected spinal segments. If new bone formation occurs in the cervical spine, it can compress nerves or the spinal cord, leading to difficulty swallowing (dysphagia) or a hoarse voice. Unlike AS, DISH is a non-inflammatory condition.
Ankylosing Spondylitis is characterized by inflammatory back pain that worsens with rest and improves with physical activity. Morning stiffness in AS lasts longer than 30 minutes and can be accompanied by buttock pain. Beyond the spine, AS can involve other joints such as the ribs, shoulders, knees, hips, or feet. AS may also present with broader symptoms like weight loss, fatigue, skin rashes, or vision changes due to inflammation in other organ systems, such as uveitis or inflammatory bowel disease.
How Doctors Distinguish Them
Doctors primarily use imaging studies to differentiate DISH from AS. X-rays are a common tool, revealing specific findings. For DISH, X-rays show “flowing ossification” along at least four continuous vertebral levels, where the connection develops around the outside of the joint.
In contrast, AS X-rays show narrowing and stiffening of the sacroiliac joints (sacroiliitis). They also reveal bone growth leading to squared vertebral discs or fusion through the middle of the vertebrae.
Magnetic Resonance Imaging (MRI) and Computed Tomography (CT) scans offer more detailed views, allowing doctors to visualize inflammatory changes in AS that are absent in DISH. Laboratory tests also play a role. Inflammatory markers like erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) are elevated in AS, but they are not relevant for diagnosing DISH. The presence of the HLA-B27 gene is a genetic risk factor associated with AS, while it is not linked to DISH.
Different Paths to Management
Management for DISH focuses on symptomatic relief and maintaining flexibility, as there is no specific treatment to reverse the bone formation. Pain can be managed with over-the-counter pain relievers, and physical therapy is recommended to maintain the range of motion in affected joints. Addressing complications like dysphagia, through surgical removal of bone spurs, may be necessary.
Ankylosing Spondylitis management aims to reduce inflammation, alleviate pain, prevent disease progression, and maintain mobility. Nonsteroidal anti-inflammatory drugs (NSAIDs) are prescribed to control inflammation and pain. For more severe cases, biologic medications, such as TNF inhibitors, are used to target specific inflammatory pathways and slow disease progression. Regular physical therapy and exercise are encouraged to preserve spinal flexibility and reduce stiffness. Lifestyle modifications, including regular exercise, are beneficial for both conditions, but they are particularly important in AS to manage inflammation and prevent further spinal fusion.