Can You DISH It Out: Comparing DISH and AS

Introduction

Diffuse Idiopathic Skeletal Hyperostosis (DISH) and Ankylosing Spondylitis (AS) are two conditions that impact the spine, but they differ significantly in their underlying causes, progression, and clinical implications. Understanding each condition individually and then comparing them is key to accurate diagnosis and effective management.

Understanding DISH

Diffuse Idiopathic Skeletal Hyperostosis (DISH) is a non-inflammatory condition characterized by excessive bone formation in ligaments and tendons, particularly the anterior longitudinal ligament of the spine. This leads to ossifications that appear as flowing "candle wax" formations on imaging, spanning at least four contiguous vertebrae. DISH is more common in individuals over 50 and has a higher prevalence in men. Among individuals over 50, it occurs in about 25% of men and 15% of women, rising to 28% and 26%, respectively, in those over 80.

DISH is often asymptomatic, discovered incidentally during imaging for unrelated issues. When symptoms occur, they include back pain, stiffness, and sometimes dysphagia or airway obstruction in cases of cervical involvement. Peripheral joint involvement, such as heel spurs or enthesopathies, is also possible. Notably, DISH is associated with metabolic conditions such as diabetes, hyperlipidemia, hypertension, and obesity, but it is not immune-mediated.

While DISH often progresses without severe symptoms, its rigidity can predispose individuals to spinal fractures. They are predisposed to fractures because the ossification of spinal ligaments creates a rigid, inflexible spine. This rigidity prevents the spine from absorbing and distributing forces effectively, making it behave like a long bone during trauma, which increases the likelihood of unstable fractures. Such fractures can be severe, leading to instability or neurological compromise, particularly in older adults.

Key takeaways

DISH is a lot more common than people think, especially in older men with associated metabolic disturbances. It is also usually asymptomatic. The only important thing to remember is to refer your patients for whole-spine CT or MRI, even when minimal trauma happens. Fractures are significantly more common in individuals with Diffuse Idiopathic Skeletal Hyperostosis (DISH), occurring up to four times more frequently than in the general population, with up to 58% of these fractures involving spinal cord injury due to the spine's rigidity and instability. Mortality rates are notably high, with studies showing a 15% mortality rate for surgically treated cervical fractures and up to 67% for those managed conservatively.

Understanding AS

Ankylosing Spondylitis (AS) is a chronic inflammatory condition primarily affecting the axial spine and sacroiliac joints. It has many names and Ben is a real stickler for it, and he once corrected me like three times during his course. This is the name I went with because it is the one currently most used and is used by the National Institute of Health (NIH). I usually just use the old name Morbus Bechterew because it sounds cool. Like a lame supervillain, but instead of destroying the world, his goal is to ruin the spines of a small subset of people. It also scares patients and makes me sound smart because it is in Latin (joke).

It typically begins before the age of 40, with 80% of people experiencing first symptoms before the age of 30.

AS presents with inflammatory back pain that improves with exercise but not with rest. Other symptoms include morning stiffness, reduced spinal mobility, and postural changes such as kyphosis in advanced stages. Extra-articular manifestations are common, including uveitis, enthesitis, inflammatory bowel disease, and cardiovascular complications. Imaging often reveals sacroiliitis and the classic "bamboo spine" caused by spinal fusion (late stage). Approximately 90-95% of people with Ankylosing Spondylitis (AS) have the HLA-B27 gene, and 50-70% of people will present with elevated CRP and sedimentation.

AS significantly increases the risk of spinal fractures due to osteoporosis and brittleness of fused vertebrae. It also increases the risk of heart disease, including aortic valve issues, arrhythmias, and coronary artery disease, due to chronic inflammation.

Key takeaways

If you get a young patient with inflammatory-like back pain that has been ongoing for a long time and improves dramatically with NSAIDs, refer them to get HLA-B27 tested, as well as sedimentation and CRP levels checked. In the early stages of the disease, there will be no or only subtle changes on imaging. The patients I saw ranged on a spectrum from severely affected to mildly inconvenienced. Educate them on the importance of regular exercise, including aerobic exercise. The more affected ones will probably need to work with or consult a physiotherapist on a semi-regular basis. Their care should be multidisciplinary and it should include a cardiologist along with all the obvious specialists.

Comparison of DISH and AS