Diffuse idiopathic skeletal hyperostosis (DISH) is a non-inflammatory disease characterized by the formation of ossification bridges along the anterior spinal surface [1]. The diagnosis is established on the basis of radiographic criteria outlined by Resnick and Niwayama in 1976, which include: 1) ossification involving four contiguous vertebrae, 2) preservation of disc height, and 3) absence of bony ankylosis at the sacroiliac or zygapophyseal joints [2]. The prevalence of DISH ranges from 3.9 % to 30.8 %, and is more common in men, older individuals, and Caucasians [[3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15]]. Ankylosis is more frequently observed in the middle and lower thoracic spine [3]. DISH is also associated with endocrine disorders such as obesity and diabetes mellitus. Clinically, individuals with DISH are prone to unstable vertebral fractures following minor trauma [16], and delayed diagnosis may result in spinal cord injury [17]. Therefore, the presence of DISH is a critical factor to consider when diagnosing spinal cord injuries.

The concept of early-phase DISH (EDISH) was recently introduced, with criteria developed and validated. DISH is defined as “ossification involving four contiguous vertebrae” based on Resnick and Niwayama's definition [2]. On the other hand, EDISH is defined as having less than three contiguous vertebrae, incomplete bony bridging, or calcification [18]. Kuperus et al. reported a 19.7 % prevalence of EDISH in non-Hispanic whites and African Americans [18], while Fournier et al. found a prevalence of 13.2 % in a predominantly white North American cohort of 1536 individuals [19]. Both studies utilized chest computed tomography (CT) for assessment, without evaluating the cervical and lumbar levels.

Because DISH in the lumbar spine can affect surgical outcomes [20], presurgical evaluation of the lumbar spine is desirable; in many cases, however, only the thoracic spine is assessed. The presence or absence of DISH is an important factor in planning spinal surgery. Previous studies have reported that ankylosing of the remaining segment may be a risk factor for lumbar reoperation in patients with DISH [21]. If EDISH can be detected early, it may be useful in planning spinal surgery. In addition, in elderly patients, prior assessment of the risk of falls and intervention to prevent falls may help prevent subsequent spinal fractures. The prevalence of DISH varies among different racial groups [22]. Often asymptomatic, the mechanisms and causes of DISH remain unclear. In medical studies, asymptomatic DISH may not be adequately evaluated. Studies involving community populations that include asymptomatic Asians are limited, and comprehensive assessments of the prevalence, bony morphology, and physical characteristics of EDISH using whole spine imaging are scarce. To our knowledge, the prevalence of EDISH within an Asian community has not been documented.

In this study, we investigated the prevalence, ossification patterns, and physical characteristics of EDISH and DISH within a Japanese community population.