Discussion
DISH is a non-inflammatory disorder of bone in which ossification of ligaments and entheses occurs. DISH may be asymptomatic or a contributor to axial and peripheral joint pain and stiffness. Risk factors for DISH include male sex, advanced age and hyperinsulinemia. DISH most commonly affects the thoracic spine, where flowing ossifications may be visible along the anterolateral aspect of the vertebral bodies, typically on the right side. Other common sites for DISH include the cervical and lumbar spine, as well as entheses in the pelvis, knees, heels and shoulders.
Most patients with DISH are discovered to have the syndrome incidentally when found on imaging.1 It can be mistaken for AS because both problems often present with back stiffness and back pain.4 Several features distinguish DISH from inflammatory spondyloarthritis. First of all, DISH most commonly presents in men 50 years or older, but AS usually presents in those younger than age 45. Patients with DISH may not complain of back pain but rather stiffness that improves with activity. However, some patients progress to having back pain as well.
Back symptoms usually start in the thoracic spine in DISH, whereas patients with AS usually develop lumbar back pain first. Patients with AS may also develop intermittent buttock pain. As DISH progresses, it can include the cervical and lumbar spine. Cervical spine enthesophytes in DISH can lead to several extra-axial symptoms, such as stridor, hoarseness, dysphagia, thoracic outlet syndrome, myelopathy and spinal stenosis.1 These complications are rare.
Both diseases, when advanced, can lead to a stooped posture, decreased range of motion, stiffness and pain throughout the cervical, thoracic and lumbar spine. To confirm the diagnosis, the most reliable way to distinguish spondyloarthritis from DISH is by incorporating radiographic and laboratory findings with the clinical presentation. Interestingly, some patients with DISH have been found to have elevated serum levels of vitamin A, whereas patients with AS have been found to have paradoxically lower levels.5
DISH is a non-inflammatory disorder of bone in which ossification of ligaments & entheses occurs.
Vitamin A, Bone Metabolism & the Development of Hyperostosis
Vitamin A is involved in bone metabolism through multiple routes. Indirectly, it is a factor in stem cell growth and differentiation. It is a component in bone formation and resorption, though the mechanism of bone formation is unclear. Regarding bone resorption, vitamin A has been found to stimulate osteoclasts to resorb bone, and at the same time inhibit the formation of osteoclasts.6
When retinoids are ingested, they attach to retinoid binding protein for uptake into peripheral cells. Vitamin A is primarily stored in the liver, but chylomicrons take one-quarter to one-third of dietary retinoids and deposit them outside the liver, with bone the next most common site for metabolism.6 Once inside cells, retinol is converted to all-trans retinol via oxidation. All-trans retinal is then oxidized to all-trans retinoic acid, which is the active compound required to properly bind to the multitude of proteins and receptors with which it interacts.
