Surgical stabilization of spinal metastasis in diffuse idiopathic skeletal hyperostosis ("Mets-on-DISH"): Two case reports.

Rationale: Diffuse idiopathic skeletal hyperostosis (DISH) is characterized by ossification along the anterolateral aspect of at least 4 contiguous vertebral bodies. A fracture involving the fused vertebra in patients with DISH often leads to severe instability and spinal cord injury. Spinal metastasis (Mets) and DISH can coexist in elderly patients and increase their risk of pathologic vertebral fractures. However, there are few reports on concomitant spinal Mets and DISH. Patient concerns: A 78-year-old man who complained of gradual onset of paraparesis, sensory loss below the umbilicus, and incontinence (case 1) and a 63-year-old woman who complained of severe back pain and urinary incontinence (case 2). Diagnosis: Two patients were diagnosed with spinal Mets and DISH. Interventions: Decompression surgery was performed at the metastatic sites in case 1 whereas instrumentation surgery was performed in case 2 despite the fracture having a benign appearance with no associated neurologic symptoms. Outcomes: A vertebral fracture developed at the metastatic vertebra after decompression surgery in case 1. Severe instability of the surgical site in this case resulted in persistent paralysis even after subsequent revision surgery with instrumentation. In contrast, the clinical course was benign without any neurologic dysfunction at the 2-year follow-up in case 2. Lessons: Instrumentation surgery should be performed in patients with DISH who develop spinal Mets even if there is no apparent instability.