Not so Mutually Exclusive Diseases: A Case of Co-occurrence of Inflammatory Spondyloarthritis and Diffuse Skeletal Hyperostosis in a Young Patient

Diffuse idiopathic skeletal hyperostosis (DISH) and axial spondyloarthritis (axial SpA) are differential diagnoses of lower back pain. While the latter is considered to be an inflammatory disease, DISH is thought to be a metabolic condition. The authors report a case of a 34-year-old man who presented with a one-year history of axial lower back pain associated to migratory polyarthritis, buttock and heel pain. Imaging revealed contiguous calcification of the anterior longitudinal ligament of the cervical segment, meeting major criteria for DISH. However, he also exhibited signs of bilateral sacroiliitis highly suggestive of axial SpA for which he initiated biological therapy. LEARNING POINTS: Although the most used criteria for diffuse idiopathic skeletal hyperostosis (DISH) were designed to exclude radiographic signs of spondyloarthritis (SpA), both conditions can be present simultaneously. There are only few case reports in the literature that demonstrate the association of the two diseases. Overlap and misperception of SpA and DISH could result in undertreatment of individual patients and have a negative impact on prognosis.