Dystrophic calcification and heterotopic ossification in fibrocartilaginous tissues of the spine in diffuse idiopathic skeletal hyperostosis (DISH)

Spatiotemporal changes in imaging features associated with diffuse idiopathic skeletal hyperostosis (DISH)

OBJECTIVES

The purpose of our study was to characterise spatiotemporal features of disease progression in people with diffuse idiopathic skeletal hyperostosis (DISH), early-phase DISH, and those not meeting either criterion who had repeated CT scans of the thoracic spine.

METHODS

A retrospective study was designed in collaboration with the Rochester Epidemiology Project to evaluate completeness of ectopic bridging across the thoracic spine and corresponding disease status over an average of 2.7 years (range from 0.2 to 15.0 years) in a cohort of 83 female and 74 male individuals.

RESULTS

Over 15% of individuals displayed changes in imaging features over time that resulted in a revised diagnosis along the continuum of DISH. Early-phase DISH was marked by new involvement of previously unaffected motion segments, estimated to occur over 2.1 years. Advanced presentations of DISH were marked by increased prevalence of complete bridging (average two of three available motion segments), estimated to occur over 2.6-2.9 years. Localised nodules of ectopic mineralisation external to and within the intervertebral disc were regularly observed in early-phase DISH.

CONCLUSIONS

This is the first characterisation of spatiotemporal features across all phases of DISH, indicating that progression of DISH is characterised by distinct features at different phases along the disease continuum. Localised nodules of mineralisation in the spinal ligaments and within the intervertebral discs coincident with early phases of the disease may be a key factor in the pathogenesis of DISH.

A new perspective on intervertebral disc calcification-from bench to bedside

Disc degeneration primarily contributes to chronic low back and neck pain. Consequently, there is an urgent need to understand the spectrum of disc degeneration phenotypes such as fibrosis, ectopic calcification, herniation, or mixed phenotypes. Amongst these phenotypes, disc calcification is the least studied. Ectopic calcification, by definition, is the pathological mineralization of soft tissues, widely studied in the context of conditions that afflict vasculature, skin, and cartilage. Clinically, disc calcification is associated with poor surgical outcomes and back pain refractory to conservative treatment. It is frequently seen as a consequence of disc aging and progressive degeneration but exhibits unique molecular and morphological characteristics: hypertrophic chondrocyte-like cell differentiation; TNAP, ENPP1, and ANK upregulation; cell death; altered Pi and PPi homeostasis; and local inflammation. Recent studies in mouse models have provided a better understanding of the mechanisms underlying this phenotype. It is essential to recognize that the presentation and nature of mineralization differ between AF, NP, and EP compartments. Moreover, the combination of anatomic location, genetics, and environmental stressors, such as aging or trauma, govern the predisposition to calcification. Lastly, the systemic regulation of calcium and Pi metabolism is less important than the local activity of PPi modulated by the ANK-ENPP1 axis, along with disc cell death and differentiation status. While there is limited understanding of this phenotype, understanding the molecular pathways governing local intervertebral disc calcification may lead to developing disease-modifying drugs and better clinical management of degeneration-related pathologies.

High Circulating FGF-23 and Its Relationship with Severity of Spinal Involvement in Diffuse Idiopathic Skeletal Hyperostosis

The primary objective of this study was to determine the role of fibroblast growth factor 23 (FGF-23) in the pathogenesis of diffuse idiopathic skeletal hyperostosis (DISH). A total of 61 patients with DISH and 61 age- and sex-matched control patients without DISH were included in this study. The serum FGF-23, creatinine, inorganic phosphate, calcium, albumin, albumin-adjusted calcium and alkaline phosphatase, and C-reactive protein were assessed in both groups. Based on the extent of ossification, DISH group was further divided into T-DISH and L-DISH subgroups. Data were comparatively analyzed between DISH and Non-DISH groups and among T-DISH, L-DISH, and Non-DISH groups, respectively. Besides, the number of ossification segments of all DISH patients was quantified and the correlation between the number of ossification segments and the serum concentration of FGF-23 was analyzed. The results revealed that serum FGF-23 was significantly higher in DISH group than in Non-DISH group, regardless of gender. Interestingly, serum Pi was significantly lower in DISH group than in Non-DISH group. Moreover, a significant difference in serum FGF-23 among T-DISH, L-DISH, and Non-DISH groups was also observed. In contrast to Non-DISH group, both T-DISH and L-DISH subgroups displayed significantly higher serum FGF-23 level. Although the mean value was relatively higher in L-DISH subgroup, no statistically significant difference was found between T-DISH and L-DISH subgroups. In addition, a moderately positive correlation was identified between the number of ossification segments and the serum level of FGF-23. It can be concluded that serum FGF-23 could serve as a positive biomarker for DISH and may play a significant role in ectopic ossification in DISH.

Not All Osteophytes Are Located on the Right Side of the Vertebrae in Diffuse Idiopathic Skeletal Hyperostosis: A Quantitative Analysis in Relation to the Position of Aorta

OBJECTIVE

Diffuse idiopathic skeletal hyperostosis (DISH) is characterized by osteophytes in the anterior vertebrae, and the presence of aorta may have an impact on their formation. However, the anatomical positional relationship between the aorta and osteophytes in patients with DISH remains controversial. This study aimed to evaluate the position of osteophytes in relation to aorta in DISH, and the influence of aortic pulsation on the formation of osteophytes from the perspective of morphology.

METHODS

We conducted a retrospective review of 101 patients diagnosed with DISH and symptomatic lumbar spinal stenosis between June 2018 and December 2021. A total of 637 segments with heterotopic ossification in DISH were used for quantitative measurements on CT scans. The Cartesian coordinate system was built up on the axial CT scans to reflect the relative position between aorta and osteophytes. Osteophytes were divided into adjacent aorta group (AD group) and non-adjacent aorta group (N-AD group). In terms of the morphology, osteophytes in the AD group were further divided into convex, flat, and concave types. The relative position between aorta and osteophytes, and the aorta-osteophyte distance and morphology of osteophytes were compared. Univariate analysis of variance was performed for multiple groups, and two independent-samples t-tests were used for two groups.

RESULTS

From T5 to L4, aorta gradually descended from left side to middle of vertebrae, and osteophytes gradually shifted from right side of vertebrae (T5-T10) to bilateral sides (T11-L4). Of 637 osteophytes in DISH, 60.1% (383/637) were in AD group, including convex type 0.6% (4/637), flat type 34.7% (221/637), and concave type 24.8% (158/637). The N-AD group accounted for 39.9% (254/637). Flat osteophytes were concentrated in T5-T12, while concave osteophytes in T11-L4. Overall, the aorta-osteophyte distance of concave type was significantly smaller than that of flat type.

CONCLUSION

Osteophytes are not always located on the right side of vertebrae, but move with the position of the descending aorta. Furthermore, the morphology of osteophytes varies by vertebral segment in DISH, which is related to aorta descending anteriorly in the spine.

How does diffuse idiopathic skeletal hyperostosis affect the sagittal spinopelvic alignment in lumbar spinal stenosis patients?

OBJECTIVE

To compare the differences of spinopelvic morphology among patients with DISH, patients without DISH and normal elderly and to assess the impact of ossification extent on sagittal alignment.

METHODS

Patients with and without DISH aged > 50 years who required surgery because of lumbar spinal stenosis were enrolled in this cohort(DISH and Non-DISH groups). Also, we collected age-matched normal old outpatients as the control group(Normal group). According to ossification extent, DISH group were divided into two subgroups(T-DISH and L-DISH subgroups). Spinopelvic parameters were measured. Distribution differences of Roussouly classification were analyzed between DISH and Non-DISH group, T-DISH and L-DISH subgroup, respectively. Additionally, distribution difference of kyphotic apex vertebrae between T-DISH and L-DISH subgroup was also investigated.

RESULTS

A total of 429 patients (300 males and 129 females) were enrolled in our study, with a mean age of 64.1 ± 5.8 years. Compared to the Normal group, DISH and Non-DISH groups both had significantly higher CSVA, PT, OH, SVA, TPA and lower LL, SS, C7 Tilt, SSA, SPA. Compared to Non-DISH group, DISH group, regardless of ossification extent, had significantly higher T1 slope, CSVA, TK and SVA. Besides, T-DISH subgroup showed significant higher LL, PI, SS and SSA than L-DISH subgroup. There were significant differences of Roussouly classification distribution between T-DISH and L-DISH subgroup. In terms of kyphotic apex location, compared to relatively higher locations in T-DISH subgroup, L-DISH subgroup had apical locations predominantly in the lower thoracic.

CONCLUSION

Sagittal spinopelvic alignment is influenced by the presence of DISH and the extent of ossification. Patients with L-DISH have not only increased thoracic kyphosis and forward trunk, but also insufficient lumbar lordosis.

Number of contiguous vertebral cross-links in the spine indicates bone formation: a cross-sectional study

BACKGROUND

As an indicator to evaluate the risk of fracture in diffuse idiopathic skeletal hyperostosis, the maximum number of vertebral bodies' bone cross-linked with contiguous adjacent vertebrae (max VB) was developed. This study retrospectively investigates the relationship between max VB, bone mineral density (BMD), and bone metabolic markers (BMM).

METHODS

In this cross-sectional study (from April 2010 to January 2022), males (n = 114) with various max VB from the thoracic vertebra to the sacrum, measured using computed tomography scans, were selected to assess femur BMD and BMM. The association of max VB with the total type I procollagen N-terminal propeptide (P1NP), tartrate-resistant acid phosphatase 5b (TRACP-5b), and bone turnover ratio (BTR = TRACP-5b/P1NP) as well as its relationship with femur BMD with P1NP and TRACP-5b, were investigated. Furthermore, the relationship between P1NP and TRACP-5b was investigated.

RESULTS

P1NP increased in proportion to max VB and TRACP-5b increased in proportion to P1NP. Moreover, BTR was inversely proportional to max VB. Finally, femur BMD was inversely proportional to P1NP and TRACP-5b.

CONCLUSION

As max VB increased with P1NP-a potential osteogenesis indicator-and BTR was inversely proportional to max VB with compensatory TRACP-5b increase, max VB can be considered as a possible predictor of bone fusion.

Stiffness and axial pain are associated with the progression of calcification in a mouse model of diffuse idiopathic skeletal hyperostosis

BACKGROUND

Diffuse idiopathic skeletal hyperostosis (DISH) is characterized by progressive calcification of spinal tissues; however, the impact of calcification on pain and function is poorly understood. This study examined the association between progressive ectopic spine calcification in mice lacking equilibrative nucleoside transporter 1 (ENT1^-/-), a preclinical model of DISH, and behavioral indicators of pain.

METHODS

A longitudinal study design was used to assess radiating pain, axial discomfort, and physical function in wild-type and ENT1^-/- mice at 2, 4, and 6 months. At endpoint, spinal cords were isolated for immunohistochemical analysis of astrocytes (GFAP), microglia (IBA1), and nociceptive innervation (CGRP).

RESULTS

Increased spine calcification in ENT1^-/- mice was associated with reductions in flexmaze exploration, vertical activity in an open field, and self-supporting behavior in tail suspension, suggesting flexion-induced discomfort or stiffness. Grip force during the axial stretch was also reduced in ENT1^-/- mice at 6 months of age. Increased CGRP immunoreactivity was detected in the spinal cords of female and male ENT1^-/- mice compared to wild-type. GFAP- and IBA1-immunoreactivity were increased in female ENT1^-/- mice compared to wild-type, suggesting an increase in nociceptive innervation.

CONCLUSION

These data suggest that ENT1^-/- mice experience axial discomfort and/or stiffness and importantly that these features are detected during the early stages of spine calcification.

Case Report: Unusual Heterotopic Ossification of the Hindfoot

Heterotopic ossification (HO) is a pathologic condition in which aberrant lamellar bone deposits in soft tissues, outside of the normal skeleton. Pathogenesis is still unclear, but different risk factors are known. Here we report a case of a 14 year-old girl presenting with pain in the medial calcaneal region and evidence of a rapidly growing, firm and solid neoformation. The lesion was diagnosed 6 years earlier, but it was consistently smaller and asymptomatic so that the patient did not undergo any follow up. The patient had no previous trauma or surgery, no other risk factors for HO and did not show any clinically evident HO in other districts. Xray and CT showed a heterogeneous bony lesion in the context of soft tissues, isolated from the calcaneus. After complete excision, histological analysis confirmed the diagnosis of HO. In conclusion, lone non congenital HO can occur regardless of known risk factors. Small HO lesion may also enter a proliferative phase without evidence of triggering events. More studies are required to better understand etiopathogenesis of HO in these clinical settings.

Sustained local ionic homeostatic imbalance caused by calcification modulates inflammation to trigger heterotopic ossification

Heterotopic ossification (HO) is a condition triggered by an injury leading to the formation of mature lamellar bone in extraskeletal soft tissues. Despite being a frequent complication of orthopedic and trauma surgery, brain and spinal injury, the etiology of HO is poorly understood. The aim of this study is to evaluate the hypothesis that a sustained local ionic homeostatic imbalance (SLIHI) created by mineral formation during tissue calcification modulates inflammation to trigger HO. This evaluation also considers the role SLIHI could play for the design of cell-free, drug-free osteoinductive bone graft substitutes. The evaluation contains five main sections. The first section defines relevant concepts in the context of HO and provides a summary of proposed causes of HO. The second section starts with a detailed analysis of the occurrence and involvement of calcification in HO. It is followed by an explanation of the causes of calcification and its consequences. This allows to speculate on the potential chemical modulators of inflammation and triggers of HO. The end of this second section is devoted to in vitro mineralization tests used to predict the ectopic potential of materials. The third section reviews the biological cascade of events occurring during pathological and material-induced HO, and attempts to propose a quantitative timeline of HO formation. The fourth section looks at potential ways to control HO formation, either acting on SLIHI or on inflammation. Chemical, physical, and drug-based approaches are considered. Finally, the evaluation finishes with a critical assessment of the definition of osteoinduction. STATEMENT OF SIGNIFICANCE: The ability to regenerate bone in a spatially controlled and reproducible manner is an essential prerequisite for the treatment of large bone defects. As such, understanding the mechanism leading to heterotopic ossification (HO), a condition triggered by an injury leading to the formation of mature lamellar bone in extraskeletal soft tissues, would be very useful. Unfortunately, the mechanism(s) behind HO is(are) poorly understood. The present study reviews the literature on HO and based on it, proposes that HO can be caused by a combination of inflammation and calcification. This mechanism helps to better understand current strategies to prevent and treat HO. It also shows new opportunities to improve the treatment of bone defects in orthopedic and dental procedures.

Patients with diffuse idiopathic skeletal hyperostosis have an increased burden of thoracic aortic calcifications

Objectives.

DISH has been associated with increased coronary artery calcifications and incident ischaemic stroke. The formation of bone along the spine may share pathways with calcium deposition in the aorta. We hypothesized that patients with DISH have increased vascular calcifications. Therefore we aimed to investigate the presence and extent of DISH in relation to thoracic aortic calcification (TAC) severity.

Methods.

This cross-sectional study included 4703 patients from the Second Manifestation of ARTerial disease cohort, consisting of patients with cardiovascular events or risk factors for cardiovascular disease. Chest radiographs were scored for DISH using the Resnick criteria. Different severities of TAC were scored arbitrarily from no TAC to mild, moderate or severe TAC. Using multivariate logistic regression, the associations between DISH and TAC were analysed with adjustments for age, sex, BMI, diabetes, smoking status, non-high-density lipoprotein cholesterol, cholesterol lowering drug usage, renal function and blood pressure.

Results.

A total of 442 patients (9.4%) had evidence of DISH and 1789 (38%) patients had TAC. The prevalence of DISH increased from 6.6% in the no TAC group to 10.8% in the mild, 14.3% in the moderate and 17.1% in the severe TAC group. After adjustments, DISH was significantly associated with the presence of TAC [odds ratio (OR) 1.46 [95% CI 1.17, 1.82)]. In multinomial analyses, DISH was associated with moderate TAC [OR 1.43 (95% CI 1.06, 1.93)] and severe TAC [OR 1.67 (95% CI 1.19, 2.36)].

Conclusions.

Subjects with DISH have increased TACs, providing further evidence that patients with DISH have an increased burden of vascular calcifications.

Galectin-3 Enhances Osteogenic Differentiation of Precursor Cells From Patients With Diffuse Idiopathic Skeletal Hyperostosis via Wnt/β-Catenin Signaling

Diffuse idiopathic skeletal hyperostosis (DISH) is a noninflammatory skeletal disease characterized by the progressive ectopic ossification and calcification of ligaments and enthuses. However, specific pathogenesis remains unknown. Bone marrow mesenchymal stem cells (BMSCs) are a major source of osteoblasts and play vital roles in bone metabolism and ectopic osteogenesis. However, it is unclear whether BMSCs are involved in ectopic calcification and ossification in DISH. The current study aimed to explore the osteogenic differentiation abilities of BMSCs from DISH patients (DISH-BMSCs). Our results showed that DISH-BMSCs exhibited stronger osteogenic differentiation abilities than normal control (NC)-BMSCs. Human cytokine array kit analysis showed significantly increased secretion of Galectin-3 in DISH-BMSCs. Furthermore, Galectin-3 downregulation inhibited the increased osteogenic differentiation ability of DISH-BMSCs, whereas exogenous Galectin-3 significantly enhanced the osteogenic differentiation ability of NC-BMSCs. Notably, the increased Galectin-3 in DISH-BMSCs enhanced the expression of β-catenin as well as TCF-4, whereas attenuation of Wnt/β-catenin signaling partially alleviated Galectin-3-induced osteogenic differentiation and activity in DISH-BMSCs. In addition, our results noted that Galectin-3 interacted with β-catenin and enhanced its nuclear accumulation. Further in vivo studies showed that exogenous Galectin-3 enhanced ectopic bone formation in the Achilles tendon in trauma-induced rats by activating Wnt/β-catenin signaling. The current study indicated that enhanced osteogenic differentiation of DISH-BMSCs was mainly attributed to the increased secretion of Galectin-3 by DISH-BMSCs, which enhanced β-catenin expression and its nuclear accumulation. Our study helps illuminate the mechanisms of pathological osteogenesis and sheds light on the possible development of potential therapeutic strategies for DISH treatment. © 2022 American Society for Bone and Mineral Research (ASBMR).

Abcc6 Null Mice—a Model for Mineralization Disorder PXE Shows Vertebral Osteopenia Without Enhanced Intervertebral Disc Calcification With Aging

Chronic low back pain is a highly prevalent health condition intricately linked to intervertebral disc degeneration. One of the prominent features of disc degeneration that is commonly observed with aging is dystrophic calcification. ATP-binding cassette sub-family C member 6 (ABCC6), a presumed ATP efflux transporter, is a key regulator of systemic levels of the mineralization inhibitor pyrophosphate (PPi). Mutations in ABCC6 result in pseudoxanthoma elasticum (PXE), a progressive human metabolic disorder characterized by mineralization of the skin and elastic tissues. The implications of ABCC6 loss-of-function on pathological mineralization of structures in the spine, however, are unknown. Using the Abcc6^−/− mouse model of PXE, we investigated age-dependent changes in the vertebral bone and intervertebral disc. Abcc6^−/− mice exhibited diminished trabecular bone quality parameters at 7 months, which remained significantly lower than the wild-type mice at 18 months of age. Abcc6^−/− vertebrae showed increased TRAP staining along with decreased TNAP staining, suggesting an enhanced bone resorption as well as decreased bone formation. Surprisingly, however, loss of ABCC6 resulted only in a mild, aging disc phenotype without evidence of dystrophic mineralization. Finally, we tested the utility of oral K3Citrate to treat the vertebral phenotype since it is shown to regulate hydroxyapatite mechanical behavior. The treatment resulted in inhibition of the osteoclastic response and an early improvement in mechanical properties of the bone underscoring the promise of potassium citrate as a therapeutic agent. Our data suggest that although ectopic mineralization is tightly regulated in the disc, loss of ABCC6 compromises vertebral bone quality and dysregulates osteoblast-osteoclast coupling.

Ectopic mineralisation of the mandibular symphysis in ENT1 knockout mice: A model of dystrophic calcification

Equilibrative nucleoside transporter 1 (ENT1) transfers nucleosides, such as adenosine, across plasma membranes. We reported previously that mice lacking ENT1 (ENT1 ^-/- ) exhibit progressive ectopic calcification of spinal tissues-a phenotype resembling diffuse idiopathic skeletal hyperostosis (DISH) in humans. Our objective was to investigate potential calcification of orofacial tissues in ENT1 ^-/- mice. Heads of wild-type mice and ENT1 ^-/- mice from 3 to 17 months were evaluated using microcomputed tomography (μCT). Some heads were decalcified and processed for histological assessment. Other heads were examined using energy dispersive X-ray spectroscopy and micro X-ray diffraction. Using μCT, ENT1 ^-/- mice showed extensive radiopaque lesions within the mandibular symphysis, the severity of which increased with advancing age. Histologically, at 6 months these ectopic radiopacities were found to correspond to acellular, amorphous, eosinophilic material, with no evidence of inflammatory cells. Because lesions were localised to the symphysis, we identified early pathological changes at 3 months and observed that lesions initiated specifically within the fibrocartilage pad. Energy-dispersive X-ray spectroscopy of ectopic lesions revealed large amounts of calcium and phosphorous in a molar ratio of ~1.59, and X-ray diffraction profiles matched that of calcium-deficient hydroxyapatite. This is the first characterisation of ectopic calcifications within the mandibular symphysis of ENT1 ^-/- mice, indicating a role for ENT1 and adenosine metabolism in regulating calcification of fibrocartilaginous tissues. Moreover, these murine lesions resemble areas of dystrophic calcification in the spinal tissues of humans with DISH. Importantly, ectopic calcifications develop in a reproducible temporal pattern within a well-defined anatomical region and, thus, provide a model for determining the cellular and molecular pathways underlying ectopic calcification in DISH and related disorders.

Heterotopic ossification in a patient with diffuse idiopathic skeletal hyperostosis: Input from histological findings

A high incidence of heterotopic ossification (HO) has been reported in patients with diffuse idiopathic skeletal hyperostosis (DISH), a metabolic disease characterized by calcifications of entheses at spine and peripheral sites. We performed histological and immunohistochemical analyses in five different HO sites in a patient with DISH to study a possible mutual interaction of bone morphogenetic protein 2 (BMP-2), transforming growth factor beta (TGF-β), and decorin, crucial for bone mass increasing, matrix calcification, and endochondral bone formation. We speculated that the surgical trauma triggered HO, inducing TGF-β release at the lesion site. TGF-β recruits osteoblast precursor cells and determines the overexpression of BMP-2 in the surrounding skeletal muscle, inducing a further osteogenic differentiation, contributing to HO onset.

Phylogeny and chemistry of biological mineral transport

Three physiologically mineralizing tissues - teeth, cartilage and bone - have critical common elements and important evolutionary relationships. Phylogenetically the most ancient densely mineralized tissue is teeth. In jawless fishes without skeletons, tooth formation included epithelial transport of phosphates, a process echoed later in bone physiology. Cartilage and mineralized cartilage are skeletal elements separate from bone, but with metabolic features common to bone. Cartilage mineralization is coordinated with high expression of tissue nonspecific alkaline phosphatase and PHOSPHO1 to harvest available phosphate esters and support mineralization of collagen secreted locally. Mineralization in true bone results from stochastic nucleation of hydroxyapatite crystals within the cross-linked collagen fibrils. Mineral accumulation in dense collagen is, at least in major part, mediated by amorphous aggregates - often called Posner clusters - of calcium and phosphate that are small enough to diffuse into collagen fibrils. Mineral accumulation in membrane vesicles is widely suggested, but does not correlate with a definitive stage of mineralization. Conversely mineral deposition at non-physiologic sites where calcium and phosphate are adequate has been shown to be regulated in large part by pyrophosphate. All of these elements are present in vertebrate bone metabolism. A key biological element of bone formation is an epithelial-like cellular organization which allows control of phosphate, calcium and pH during mineralization.