Diffuse idiopathic skeletal hyperostosis (DISH) : the impact of spinal ankylosis on trauma patients

Abstract

In this thesis the clinical relevance of diffuse idiopathic skeletal hyperostosis (DISH) and its associated morbidity was investigated. We focused on the current and expected prevalence of DISH in the Netherlands, the clinical outcome of patients with an ankylosing spinal disorder (ASD) after spinal fractures and the characteristics of the ‘flowing wax’ morphology of DISH with respect to fracture mechanisms specific for this condition. We demonstrated that the prevalence of DISH in the Netherlands was higher than expected and relatively high compared to other sources in literature. By means of logistic regression analysis we demonstrated that the diagnosis DISH was statistically significant related to male gender and increasing age. In cadaveric spines with DISH the ossification mass was measured with CT scanning, demonstrating that the ossification mass was maximal at the level of the intervertebral disc (IVD) and minimal at the level of the vertebral body. This finding may explain the predilection for fractures through the vertebral body in DISH; since the ossifications provide a solid bridge spanning over the IVD space between two adjacent endplates, the vertebral body becomes the weakest link in the DISH affected spine. We also demonstrated that the vertebral segmental arteries were consistently localized at the mid-vertebral level, where the ossification was minimal, in both DISH specimens and controls. These findings suggest that new bone formation does not take place in the proximity of vascular structures. It was demonstrated that bone mineral density (BMD) was not elevated in the vertebral body in DISH. We measured BMDs in cadaveric human spines with DISH from different experimental orientations, either including or excluding the soft tissue ossifications in the DXA scanning field, and compared the results with control specimens. The ossifications projected in the field of view influenced BMD measurements, depending on the orientation in which BMD was measured. BMDs in the (unaffected) left half of the anteroposterior scan did not significantly differ from control BMDs. The findings of this study imply that BMD measurements in DISH patients may be unreliable when the ossifications are present in the field of view. Finally we investigated whether the presence of an ASD influenced clinical outcome after a spinal fracture. We performed a literature review and a retrospective review of patients at our own institution. The outcome of patients with ASD was considerably poorer than the general trauma population. Patients with ASD were admitted more frequently with a neurological deficit associated with their injury, leading to higher complication and mortality rates. Establishing a timely diagnosis was more difficult in patients with ankylosing spondylitis (AS) and DISH, because fractures often resulted from trivial trauma and were masked or obscured on radiographs because of pathological osseous changes. Because of unstable (hyperextension) fracture configurations, operative treatment may be beneficial over nonoperative treatment in this patient category. Because of global demographic ageing and the increase in metabolic conditions such as obesity and type 2 diabetes mellitus, which are highly related to DISH and have become endemic in the past few decades, the prevalence of DISH will increase in the future. Therefore, clinicians should be prepared to care for more trauma patients with DISH.