Prevalence of diffuse idiopathic skeletal hyperostosis in Budapest, Hungary

High prevalence of diffuse idiopathic skeletal hyperostosis (DISH) among obese young patients - A retrospective observational study

OBJECTIVE

Diffuse idiopathic skeletal hyperostosis (DISH) is characterized by ossification of ligaments and entheses, and most commonly affects the spinal column. The prevalence of DISH is increasing with age and is considered uncommon before the age of 50 years, with an estimated prevalence of less than 5 %. DISH is known to be highly associated with metabolic syndrome and obesity. We aim to assess the prevalence of DISH among young (≤50 yr.) patients suffering from severe obesity (BMI of 35 kg/m2 or higher).

METHODS

A retrospective analysis assessing chest and spine radiographs (including Computed Tomography, CT) of patients with BMI≥35 visiting the bariatric ambulatory clinic in an academic medical center from 2013 to 2022. Patients included in the analysis were 31-50 years old. Diagnosis of DISH was made according to the Resnick criteria. The prevalence of DISH was calculated. Demographic, clinical and laboratory data were collected and compared between the DISH and non-DISH groups.

RESULTS

183 young (mean age: 40.4; 118 females, 64.2 %) obese (BMI median: 40.6; range 35-73) patients were included in the radiographic review. DISH was diagnosed in 33 patients (18.0 %; 95 % CI: 13.1-24.2 %) which was significantly higher than the expected 10 % (Z = 3.62, p<.001); another 8 patients (4.4 %; 95 % CI: 2.2-8.4 %) were considered as "near DISH" (not fulfilling yet the Resnick criteria) as it represents a pre-disease state. Patients diagnosed with DISH were significantly older than patients without DISH (t = 4.54, p<.001), as the prevalence of DISH increased by age (linear association=14.95, p<.001). There was a statistically significantly higher prevalence of hypertension (χ2 = 8.30, p<.004), smoking (χ2 = 4.69, p<.03) and OSA (χ2 = 6.16, p<.013) in the DISH group as compared to their non-DISH counterparts.

CONCLUSION

The prevalence of DISH among obese young patients was 18 %, which is much higher than in the general population. Early-onset DISH should be regarded as a musculoskeletal obesity-related complication.

DISHphagia – A Riddle Unwrapped a Clinical Case with Literature Review

Diffuse idiopathic skeletal hyperostosis (DISH) is a common but underdiagnosed systemic skeletal disease. It is characterized by calcifications affecting mainly the spinal anterior longitudinal ligament. In the majority of cases, the patients are asymptomatic, but cervical osteophytes can sometimes cause hoarseness, dysphagia (DISHphagia) and even dyspnea.

Case description: A 61-year-old man was admitted to our department with complaints of difficulty in swallowing and weight loss. Dysphagia had been increasing gradually for nine months. Barium swallow esophagram revealed asymmetric swallowing with expansion above the upper esophageal sphincter without other abnormalities. The extension was confirmed by esophago-gastro-duodenoscopy (EGD). Furthermore, CT scan of the thorax clearly demonstrated degenerative changes of the cervical and thoracic region, extensive ossification of the anterior longitudinal ligament, and osteophytes from C2-C7 with a forward displacement of the esophagus by 14 mm. The so-called “wax dripping down the candle” phenomenon was as well observed.

Conclusion: DISH is a systematic, musculo-skeletal disease of older adults with unknown etiology. Dysphagia is the most common symptom of the disease and might be caused by osteophytes of the cervical region. We presented a case of DISH with a rare localization of the osteophytes in the cervical region C2-C7. Due to the increasing incidence of the Forestier’s syndrome and its associated “DISHphagia”, the gastroenterologist should increase the awareness of this underestimated disease and improve the diagnostic approach.

Female with Ankylosing Spondylitis from the 7th–6th century BCE Lori Berd burial (Armenia)

A female skeleton from the Lori Berd archaeological cemetery, located near the city of Stepanavan (Lori Province of Armenia) is described. Palaeopathological analysis revealed a variety pathology (ankylosis of the sacroiliac joints, ankylosis of the vertebrae, syndesmophytes, ankylosed of the costovertebral and costotransverse joint fusions, kyphosis, lordosis, fracture of the anterior inferior iliac spine and traumatic lesions). This paper reports a new case of ankylosing spondylitis in a skeleton and a differential diagnosis performed to determine the etiology of the condition. The vertebral bodies remodel and together with the associated syndesmophytes form a continuous, smooth bone surface that is sometimes referred to as “bamboo spine”. In this skeleton changes in the spine, ribs, the sacrum, acetabulum, head of the femur and greater trochanter, as well as the anterior inferior iliac spine are typical of ankylosing spondylitis in advanced stage. Addtionally, there were signs of a traumatic death with injuries sustained to the scapula and vertebra. Using osteological markers in combination with the reconstruction of the archaeological context, the burial pattern suggests that the pathology the female suffered was likely due to her physical deficiencies.

Skeletal evidence of Diffuse Idiopathic Skeletal Hyperostosis (DISH) in a collective burial from Byzantine Greece

The paper reports on a collective burial from a 13th c. AD cist grave in Attica, Greece. The grave was located inside a basilica and held the remains of at least ten adults. Bone representation analysis showed secondary manipulation of previous deceased including long bone selection for reburial in the same grave and/or bones transported from a different burial place. Paleopathological analysis used macroscopy and radiology, and revealed several lesions on the axial and appendicular skeleton expressed mainly by spinal ligament ossification and multiple peripheral enthesopathies. Individuation of the remains pointed to a middle-aged male with DISH, a condition often correlated to high social rank. Byzantine period is marked by increasing development and prosperity in Greece including among others the creation of many local monastic centers. Although the precise social and professional profile of these individuals cannot be revealed, the combined investigation of skeletal and archaeological evidence suggests that the grave gathered the remains of individuals belonging to an upper class social group.

Forestier syndrome presenting with dysphagia: case report of a rare presentation

Diffuse idiopathic skeletal hyperostosis (DISH) (Forestier syndrome) is a rheumatologic disease, the etiology of which is not exactly known. It is characterized by spinal osteophyte formations resulting from the ossification of the paravertebral ligaments and muscles. Anterior longitudinal ligament is the usual site of involvement and the frequency of the disease increases after the 5th decade. Lower cervical segments are the most frequently involved regions whereas the upper cervical involvement leading to dysphagia is very rare. In this report, a 77-year-old patient with Forestier syndrome in upper cervical region presenting with dysphagia was presented. Anterior cervical osteophyte resection was performed with no need for discectomy, fusion or stabilization. The patient showed a significant improvement in his all preoperative symptoms, and no recurrence was detected at 1-year follow-up.

Diffuse Idiopathic Skeletal Hyperostosis: Persistent Sore Throat and Dysphagia in an Elderly Smoker Male

Diffuse idiopathic skeletal hyperostosis (DISH) is rarely symptomatic. However, it can present with dyspnea, hoarseness, dysphagia, and stridor. An 80-year-old chronic smoker male presented with 6-month history of sore throat and progressive dysphagia. Computed tomography of the neck revealed bulky anterior bridging syndesmophytes along the anterior aspect of the cervical spine and facet effusion involving four contiguous vertebrae consistent with DISH. Dysphagia secondary to DISH was diagnosed. Fiberoptic laryngoscopy showed bilateral vocal cord paralysis. Patient's airway became compromised requiring tracheostomy tube placement. After discussion of therapeutic options, patient agreed on a percutaneous endoscopic gastrostomy tube insertion for nutritional support. Osteophytectomy was left to be discussed further.

CT Abnormalities in the Sacroiliac Joints of Patients With Diffuse Idiopathic Skeletal Hyperostosis

OBJECTIVE

The purpose of this study is to characterize sacroiliac joints (SIJs) findings at CT of patients with diffuse idiopathic skeletal hyperostosis (DISH), a condition characterized (using the Resnick classification criteria) by ossification of at least four contiguous vertebrae in the thoracic spine and preserved disk space, but without radiographic evidence of intraarticular SIJ abnormalities.

MATERIALS AND METHODS

Pelvic CT examinations of 104 patients with DISH (fulfilling the Resnick criteria on spinal CT) and 106 age- and sex-matched control subjects whose entire spine lacked CT evidence of DISH (total, 149 men and 61 women; mean [± SD] age, 72.3 ± 8.7 years) were retrospectively evaluated for the presence of intra- and extraarticular bridging osteophytes, spurs, subchondral cystlike changes, erosions, and sclerosis of SIJs. Excluded were patients with known ankylosing spondylitis or inflammatory-related diseases. Data were analyzed using multivariate ANOVA to examine the degree of difference between patients with DISH and control subjects. Logistic regression analysis was used to generate odds ratios to examine their discriminatory ability. ROC analysis was then applied to examine the sensitivity and specificity of the results.

RESULTS

The frequency of anterior bridging, posterior bridging, entheseal bridging, and joint ankylosis was significantly higher among patients with DISH compared with control subjects (48% vs 9%, 20% vs 1%, 34% vs 4%, and 23% vs 0%, respectively; p < 0.001 for all comparisons).

CONCLUSION

Intraarticular ankylosis seen at CT, an entity not included in the Resnick classification criteria, is common among patients with DISH, which implies that the radiologic classification criteria for DISH need to be revised.

Bone-formers and bone-losers in an archaeological population

Objectives

Recent biomedical research suggests that, in modern human populations, individuals may vary in their inherent tendency toward bone formation at skeletal and extra‐skeletal locations. However, the nature of this phenomenon is incompletely understood, and the extent to which it might apply to past populations is unclear. It is hypothesized that if there is inter‐individual variation in some overall tendency toward bone formation in skeletal and extra‐skeletal sites then there should be a positive relationship between ligamentous ossification and thickness of cortical bone. This work is a test of this hypothesis in an archaeological population.

Materials and Methods

The study material comprises adult skeletons (N = 137 individuals) of documented age at death from 18th to 19th century London. It examines the relationship between bone deposition in the anterior longitudinal ligament (ALL) in the thoracic spine and cortical index (CI) at the metacarpal measured by radiogrammetry.

Results

Controlling for the potential confounders age, sex, skeletal completeness, occupation (males) and parity (females), there was a positive association between ossification into the ALL and CI. This reflects lesser medullary cavity width in those showing ALL ossification.

Discussion

Ligamentous ossification in the axial skeleton and peripheral cortical bone status are linked, individuals with ALL ossification showing lesser resorption of cortical bone at the endosteal surface. This is consistent with the idea of inter‐individual variation in some general bone‐forming/bone‐losing tendency in this 200 year old study population, but there was no evidence of a link between ALL ossification and increased skeletal subperiosteal bone deposition. Am J Phys Anthropol 159:577–584, 2016. © 2015 The Authors American Journal of Physical Anthropology Published by Wiley Periodicals, Inc.

Prevalence of diffuse idiopathic skeletal hyperostosis (DISH) of the whole spine and its association with lumbar spondylosis and knee osteoarthritis: the ROAD study

We aimed to assess the prevalence of diffuse idiopathic skeletal hyperostosis (DISH) and its association with lumbar spondylosis (LS) and knee osteoarthritis (KOA) using a population-based cohort study entitled Research on Osteoarthritis/osteoporosis Against Disability (ROAD). In the baseline ROAD study, which was performed between 2005 and 2007, 1,690 participants in mountainous and coastal areas underwent anthropometric measurements and radiographic examinations of the whole spine (cervical, thoracic, and lumbar) and both knees. They also completed an interviewer-administered questionnaire. Presence of DISH was diagnosed according to Resnick criteria, and LS and KOA were defined as Kellgren-Lawrence (KL) grade ≥3. Among the 1,690 participants, whole-spine radiographs of 1,647 individuals (97.5%; 573 men, 1,074 women; mean age, 65.3 years) were evaluated. Prevalence of DISH was 10.8% (men 22.0%, women 4.8%), and was significantly higher in older participants (presence of DISH 72.3 years, absence of DISH 64.4 years) and mainly distributed at the thoracic spine (88.7%). Logistic regression analysis revealed that presence of DISH was significantly associated with older age [+1 year, odds ratio (OR): 1.06, 95% confidence interval (CI): 1.03-1.14], male sex (OR: 5.55, 95% CI: 3.57-8.63), higher body mass index (+1 kg/m(2), OR: 1.08, 95% CI: 1.02-1.14), presence of LS (KL2 vs KL0: 1, OR: 5.50, 95% CI: 2.81-10.8) (KL ≥3 vs KL0: 1, OR: 4.09, 95% CI: 2.08-8.03), and presence of KOA (KL ≥3 vs KL0: 1, OR: 1.89, 95% CI: 1.14-3.10) after adjusting for smoking, alcohol consumption, and residential area (mountainous vs coastal). This cross-sectional population-based study clarified the prevalence of DISH in general inhabitants and its significant association with LS and severe KOA.

Diffuse idiopathic skeletal hyperostosis: clinical features and pathogenic mechanisms

Diffuse idiopathic skeletal hyperostosis (DISH) is a systemic condition characterized by the ossification and calcification of ligaments and entheses. DISH is observed on all continents and in all races, but most commonly in men over 50 years of age. Although DISH is asymptomatic in most individuals, the condition is often an indicator of underlying metabolic disease, and the presence of spinal or extraspinal ossifications can sometimes lead to symptoms including pain, stiffness, a reduced range of articular motion, and dysphagia, as well as increasing the risk of unstable spinal fractures. The aetiology of DISH is poorly understood, and the roles of the many factors that might be involved in the development of excess bone are not well delineated. The study of pathophysiological aspects of DISH is made difficult by the formal diagnosis requiring the presence of multiple contiguous fully formed bridging ossifications, which probably represent advanced stages of DISH. In this Review, the reader is provided with an up-to-date discussion of the epidemiological, aetiological and clinical aspects of DISH. Existing classification criteria (which, in the absence of diagnostic criteria, are used to establish a diagnosis of DISH) are also considered, together with the need for modified criteria that enable timely identification of early phases in the development of DISH.

Musculoskeletal disorders in the elderly

Musculoskeletal disorders are among the most common problems affecting the elderly. The resulting loss of mobility and physical independence can be particularly devastating in this population. The aim of this article is to present some of the most frequent musculoskeletal disorders of the elderly, such as fractures, osteoporosis, osteoarthritis, microcrystal disorders, infections, and tumors.

Thoracic vertebral body fracture after total hip replacement in diffuse idiopathic skeletal hyperostosis

This article describes the critical clinical sequelae of a patient with diffuse idiopathic skeletal hyperostosis who sustained an acute iatrogenic thoracic vertebral body fracture with subsequent spinal cord injury after a total hip replacement, with a final lethal course.A 57-year-old woman was referred to the authors' institution after undergoing a total hip replacement in the supine position for secondary osteoarthritis. Postoperatively, the patient had symptoms of an incomplete paraplegia. Computed tomography scan and magnetic resonance imaging revealed diffuse idiopathic skeletal hyperostosis and an acute unstable fracture of T11 with spinal contusion. A posterior spinal fusion of T10-L1 with laminectomy of T11 was performed immediately on admission. Postoperatively, no improvement of the neurological deficit was observed. After developing multiorgan failure while in intensive care, the patient died 2 months after the total hip replacement.The morphological and functional symptoms of diffuse idiopathic skeletal hyperostosis with the typical ossification of the longitudinal ligaments and the associated loss of bending forces of the spine were detected postoperatively. This severe case demonstrates that the surgeon must be alert to possible complications due to intraoperative maneuvers in patients with stiffened spinal disorders undergoing total hip replacement.

Ossification of the posterior longitudinal ligament: pathogenesis, management, and current surgical approaches. A review

Ossification of the posterior longitudinal ligament (OPLL) is an important cause of cervical myelopathy that results from bony ossification of the cervical or thoracic posterior longitudinal ligament (PLL). It has been estimated that nearly 25% of patients with cervical myelopathy will have features of OPLL. Patients commonly present in their mid-40s or 50s with clinical evidence of myelopathy. On MR and CT imaging, this can be seen as areas of ossification that commonly coalesce behind the cervical vertebral bodies, leading to direct ventral compression of the cord. While MR imaging will commonly demonstrate associated changes in the soft tissue, CT scanning will better define areas of ossification. This can also provide the clinician with evidence of possible dural ossification. The surgical management of OPLL remains a challenge to spine surgeons. Surgical alternatives include anterior, posterior, or circumferential decompression and/or stabilization. Anterior cervical stabilization options include cervical corpectomy or multilevel anterior cervical corpectomy and fusion, while posterior stabilization approaches include instrumented or noninstrumented fusion or laminoplasty. Each of these approaches has distinct advantages and disadvantages. While anterior approaches may provide more direct decompression and best improve myelopathy scores, there is soft-tissue morbidity associated with the anterior approach. Posterior approaches, including laminectomy and fusion and laminoplasty, may be well tolerated in older patients. However, there often is associated axial neck pain and less improvement in myelopathy scores. In this review, the authors discuss the epidemiology, imaging findings, and clinical presentation of OPLL. The authors additionally discuss the merits of the different surgical techniques in the management of this challenging disease.

Diffuse idiopathic skeletal hyperostosis (DISH): relation to vertebral fractures and bone density

Radiographs and spinal bone mineral density (BMD) were evaluated from 342 elderly men regarding possible effects of diffuse idiopathic skeletal hyperostosis (DISH) on vertebral fractures and densitometry measurements. Prevalent vertebral fractures were more frequent among men with DISH compared to men with no DISH even after fracture prevalence was adjusted for BMD. Paravertebral calcifications should be considered in patients with DISH when interpreting BMD measurements because both dual X-ray absorptiometry (DXA) and quantitative CT (QCT) densitometry may not be reliable.

INTRODUCTION

The purpose of this study is to evaluate the prevalence of DISH in older men and its association with vertebral fractures and with BMD determined by DXA and QCT.

METHODS

Lateral radiographs of the spine were analyzed in a sample of 342 men aged ≥ 65 years participating in the MrOS Study concerning the presence and grade of DISH and vertebral fractures. Lumbar BMD was measured by both DXA (areal, grams per square centimeter) and QCT (volumetric, grams per cubic centimeter). The association between DISH, BMD, and presence of fractures was studied using χ ( 2 ) and t tests.

RESULTS

DISH was present in 52% (178/342) of the men. Men with DISH were older (mean, 75.1 vs 73.3, p < 0.05) and more likely to have prevalent fractures (28% vs 20%, p < p = 0.09). BMD assessed with DXA (1.08 vs 1.00 g/cm(2), p ≤ 0.0001), but not with QCT (0.11 vs 0.11 g/cm3, p = 0.65), was significantly higher in men with DISH compared to men without DISH. Significantly lower BMD of men with both DISH and fractures compared to men with DISH but without fractures was only detected by QCT (-25%, 0.09 vs 0.12, p < 0.05). Both DXA BMD and QCT BMD were significantly higher in severe lumbar DISH (+22% and +31%, p < 0.0001), respectively.

CONCLUSION

DISH was associated with a higher prevalence of vertebral fractures in elderly men. Lumbar ossifications related to DISH should be considered when interpreting BMD measurements to predict their fracture risk.

Diffuse idiopathic skeletal hyperostosis and its relation to back pain among older men: the MrOS Study

OBJECTIVES

To estimate the prevalence of diffuse idiopathic skeletal hyperostosis (DISH) in a cross-sectional study of elderly men age 65 to 100 years and to examine back and neck pain as possible correlates of DISH.

METHODS

DISH was defined using Resnick's criteria and scored according to Mata on lateral spine radiographs of 298 randomly selected participants from the MrOS Study. Standardized self-reported questionnaires were used to assess the frequency and severity of back and neck pain, and the relation of these to DISH status was estimated with χ(2) tests, as well as prevalence ratios and 95% confidence intervals using log-binomial regression models.

RESULTS

DISH was observed in 126 older men (42%), increased with age (30%, 39%, 48%, and 56% for ages 65-69, 70-74, 75-79, and ≥80 respectively), and was positively associated with body mass index (BMI) (P = 0.04) and blood pressure (P = 0.02). Significantly less back pain in the past 12 months was reported among men with DISH as compared to men without (59% vs 71%, P = 0.03), which remained after adjustment for age, BMI, and blood pressure (prevalence ratios = 0.73, 95% confidence interval = 0.57-0.95). Back pain severity (P = 0.07) and frequency (P = 0.06) were also less frequent among men with DISH compared to men without, whereas reported neck pain was similar between groups (P = 0.39).

CONCLUSIONS

Among community-dwelling elderly men, DISH prevalence is high, increases with age, and is positively associated with BMI and blood pressure. Frequency of self-reported back pain over the past 12 months was lower in older men with DISH as compared to those without DISH.

Enthesopathy formation in the humerus: Data from known age-at-death and known occupation skeletal collections

Enthesopathies, in the guise of musculoskeletal skeletal stress markers (MSM), have been widely used to reconstruct activity levels in human skeletal populations. In general, studies have focused on their presence in the upper limb, which is used in the majority of daily activities. The aim of this study was to use some of the attachment sites on the humerus to explore the relationship between enthesopathy formation, activity, and the ageing process. The skeletal sample used in this study comprised male adult skeletons with known age-at-death and known occupations from the late-19th and early-20th century cemeteries in Portugal. The enthesopathies were recorded as either present or absent. Statistical analysis using Fishers exact tests and logistic regression was undertaken to determine whether associations could be found between specific activities or socioeconomic status (manual or nonmanual workers), and age and enthesopathy presence. Left and right sides were analyzed separately. Fisher's exact tests were used to determine the relationship between activity and enthesopathy, and they demonstrated no association between activity and enthesopathies (P > 0.01). The results of the logistic regression established that age was the single most significant factor in enthesopathy formation (P > 0.05). This study found that, in these samples, age-at-death, and therefore age-related degeneration rather than degeneration caused by activities, was the primary cause of enthesopathy formation. Considering the difficulties of reliably ageing adult human skeletal remains, this is a major issue for studies of activity using enthesopathies.

Diffuse idiopathic skeletal hyperostosis in ancient clergymen

Diffuse idiopathic skeletal hyperostosis (DISH) is a common but often unrecognized systemic disorder observed mainly in the elderly. DISH is diagnosed when the anterior longitudinal ligament of the spine is ossified on at least four contiguous spinal levels or when multiple peripheral enthesopathies are present. The etiology of DISH is unknown but previous studies have shown a strong association with obesity and insulin-independent diabetes mellitus. DISH can lead to back pain, dysphagia, myelopathy, musculoskeletal impairment and grossly unstable spine fractures after minor trauma. In archeological studies a high prevalence of DISH has been demonstrated in ancient clergymen. The present study describes the pathological changes of human remains excavated from the abbey court (Pandhof) in the city of Maastricht, The Netherlands. Human remains of 51 individuals buried between 275 and 1795 ce were excavated and examined. The remains were investigated according to a standardized physical anthropological report and individuals demonstrating ossification of spinal ligaments and/or multiple peripheral enthesopathies were included in the study group. The authors reviewed all available material and after reaching consensus, each abnormality found was given a diagnosis and subsequently recorded. After examination, 28 individuals were considered to be adult males; 11 adult females; three adults of indeterminate sex and nine individuals were of sub adult age. The mean age at death for adults was 36.8 years. Seventeen adult individuals (40.4% of all adults), displayed ossifications of at least four contiguous spinal levels and/or multiple enthesopathies of the appendicular skeleton and were therefore, assigned the diagnosis DISH. The mean age of these individuals was 49.5 ± 13.0 years. In at least three of these individuals, DISH had led to extensive ossification and subsequent ankylosis of axial and peripheral skeletal structures. In this population of (presumably) clergymen and high-ranking citizens, DISH was observed in unusual high numbers at a relatively young age. Some of the examined cases suggest that DISH may be a seriously incapacitating disorder when the more advanced stages of the disease have been reached. It is hypothesized that “a monastic way of life” can predispose to DISH. Present demographic trends in obesity and diabetes mellitus as potential co-factors for the development of DISH warrant further study to investigate its future prevalence.

Ossification of the Posterior Longitudinal Ligament: An Update on Its Biology, Epidemiology, and Natural History

SIGNIFICANT PROGRESS HAS been achieved in basic research during the past decade on the pathogenesis of ossification of the posterior longitudinal ligament (OPLL), a multifactorial disease in which complex genetic and environmental factors interact. A review of the literature was conducted to update recent findings on the biology, epidemiology, natural history, and related diseases of OPLL. Gene analysis studies found specific polymorphisms that may be associated with OPLL in several collagen genes, which encode for extracellular matrix proteins. Polymorphisms in the nucleotide pyrophosphate gene, which is involved in regulation of calcification in chondrocytes, may also be associated with OPLL. However, the results of the gene analysis studies have not always been consistent. Involvement of many growth factors and cytokines, including bone morphogenic proteins and transforming growth factor-β, has been demonstrated in various histochemical and cytochemical analyses. Several transcription factors involved in cellular differentiation may also have a role. Recent epidemiological studies reaffirmed an earlier finding that diabetes mellitus is a distinct risk factor for OPLL. The long-term follow-up studies of OPLL patients are disclosing the natural history, as well as the frequency and rate of progression, of OPLL after surgical intervention. Further knowledge on the factors responsible for progression of OPLL may predict its behavior in each patient, and treatment may be tailored accordingly. The coexistence of OPLL with other diseases of ectopic ossification of the spine, such as ossification of the ligamentum flavum and diffuse idiopathic skeletal hyperostosis, is not uncommon. Scientific breakthrough in those diseases may, in turn, give insights into the pathogenesis of OPLL.