Ossification of the posterior longitudinal ligament in vitamin D-resistant rickets: case report and review of the literature

Adult rheumatologic features, treatment and complications of X-linked hypophosphatemia

X-linked hypophosphatemia (XLH) is a rare genetic phosphate disorder caused mainly by PHEX mutations. Unlike for children, knowledge of the disease's manifestations in adults is limited. Musculoskeletal symptoms are the main feature of the disease in young adults associated with a heavy burden on patients' life. They include fractures and pseudofractures, pain, joint stiffness, osteoarthritis, enthesopathies, and muscle weakness, eventually leading to impaired quality of life. Conventional treatment with phosphate supplements and vitamin D analogs is indicated in symptomatic patients. Appropriate rehabilitation is also a key to the management of the disease to improve physical function and decrease pain, stiffness, and fatigue. Regarding the incidence and consequences of musculoskeletal features in XLH, all patients should be assessed by a bone disease specialist and, if necessary, managed by a multidisciplinary team.

Contribution of imaging to the diagnosis and follow up of X-linked hypophosphatemia

X-linked hypophosphatemia (XLH) is the most common form of inheritable rickets. The disease is caused principally by PHEX mutations leading to increased concentrations of circulating intact FGF23, hence renal phosphate wasting, hypophosphatemia, and decreased circulating levels of 1,25(OH)₂ vitamin D. The chronic hypophosphatemia leads to rickets and osteomalacia through a combination of mechanisms, including a lack of endochondral ossification and impaired mineralization. Imaging has a major role in determining the diagnosis of rickets and its cause, detecting complications as early as possible, and helping in treatment monitoring.

Dental-craniofacial manifestation and treatment of rare diseases

Rare diseases are usually genetic, chronic and incurable disorders with a relatively low incidence. Developments in the diagnosis and management of rare diseases have been relatively slow due to a lack of sufficient profit motivation and market to attract research by companies. However, due to the attention of government and society as well as economic development, rare diseases have been gradually become an increasing concern. As several dental-craniofacial manifestations are associated with rare diseases, we summarize them in this study to help dentists and oral maxillofacial surgeons provide an early diagnosis and subsequent management for patients with these rare diseases.

Outcome of adult patients with X-linked hypophosphatemia caused by PHEX gene mutations

X-linked hypophosphatemia (XLH) is the most common monogenic disorder causing hypophosphatemia. This case-note review documents the clinical features and the complications of treatment in 59 adults (19 male, 40 female) with XLH. XLH is associated with a large number of private mutations; 37 different mutations in the PHEX gene were identified in this cohort, 14 of which have not been previously reported. Orthopaedic involvement requiring surgical intervention (osteotomy) was frequent. Joint replacement and decompressive laminectomy were observed in those older than 40 years. Dental disease (63%), nephrocalcinosis (42%), and hearing impairment (14%) were also common. The rarity of the disease and the large number of variants make it difficult to discern specific genotype-phenotype relationships. A new treatment, an anti-FGF23 antibody, that may affect the natural history of the disease is currently being investigated in clinical trials.

X-Linked Hypophosphatemia and FGF23-Related Hypophosphatemic Diseases: Prospect for New Treatment

Phosphate plays essential roles in many biological processes, and the serum phosphate level is tightly controlled. Chronic hypophosphatemia causes impaired mineralization of the bone matrix and results in rickets and osteomalacia. Fibroblast growth factor 23 (FGF23) is a bone-derived hormone that regulates phosphate metabolism. FGF23 excess induces hypophosphatemia via impaired phosphate reabsorption in the renal proximal tubules and decreased phosphate absorption in the intestines. There are several types of genetic and acquired FGF23-related hypophosphatemic diseases. Among these diseases, X-linked hypophosphatemia (XLH), which is caused by inactivating mutations in the phosphate-regulating endopeptidase homolog, X-linked (PHEX) gene, is the most prevalent form of genetic FGF23-related hypophosphatemic rickets. Another clinically relevant form of FGF23-related hypophosphatemic disease is tumor-induced osteomalacia (TIO), a paraneoplastic syndrome associated with FGF23-producing tumors. A combination of active vitamin D and phosphate salts is the current medical therapy used to treat patients with XLH and inoperative TIO. However, this therapy has certain efficacy- and safety-associated limitations. Several measures to inhibit FGF23 activity have been considered as possible new treatments for FGF23-related hypophosphatemic diseases. In particular, a humanized monoclonal antibody for FGF23 (burosumab) is a promising treatment in patients with XLH and TIO. This review will focus on the phosphate metabolism and the pathogenesis and treatment of FGF23-related hypophosphatemic diseases.

Extensive ossification of the paraspinal ligaments in a patient with vitamin D-resistant rickets: Case report with literature review

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This is the case of a 64-year-old woman with VDRR and extensive spinal ossification.

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This case was followed up for over 30 years.

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Imaging studies demonstrated fusion of the entire spine below the C2 vertebra.

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Mobility at the craniovertebral junction caused C1-level spinal cord compression.

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The pathology mimicked ankylosing spondylitis.

Introduction

Ectopic ossification of the spinal ligaments is not uncommon in patients with Vitamin D-resistant rickets (VDRR), but the long-term consequences of this condition have not been reported.

Presentation of case

The case was a 65-year-old female with VDRR who reported progressive weakness of the upper extremities, difficulty walking, neck pain, and numbness in the left arm. Imaging studies demonstrated cord compression with ectopic ossification at the rim of the occipital bone and OPLL at C1 level. Ankylosis of the whole spine below the C2 vertebra was also noted with preserved mobility only at the craniovertebral junction.

Discussion

Our report showed that ectopic ossification of the spinal ligament can result in ankylosis of the entire spine in patients with VDRR. In such patients, the segments with remaining mobility are considered to be at high risk of developing myelopathy due to increased stress at the junction.

Conclusion

The present case underscores the importance of providing long-term follow-up in VDRR patients presenting with ectopic ossification of the spinal ligaments. In particular, physicians should pay close attention to the possibility of myelopathy in any segments with preserved mobility.

Investigation of ossification in the posterior longitudinal ligament using micro-focus X-ray CT scanning and histological examination

BACKGROUND

Ossification in the posterior longitudinal ligament (PLL) correlates with changes of enthesis during the early stages of development, but this issue remains controversial, as little is known regarding the details of this process. The aim of the present study was to elucidate part of the ossification mechanism. Thus, in the present study, we observed and evaluated minute ossifications in the PLL that did not exhibit symptoms of ossification of the posterior longitudinal ligament (OPLL).

METHODS

The subjects in the present study were derived from serial autopsy cases from January 2009 to December 2013 at Toho University Omori Medical Center, Japan. Minute ossifications in the PLL from autopsy subjects without any history of OPLL were screened as high-density areas using micro-focus X-ray CT, and the foci were histologically examined. Subsequently, we conducted both micro-focus X-ray CT image analysis and histological examination, and evaluated the correlation between these findings and putative predictive factors reported in previous studies.

RESULTS

A total of 103 individuals among the 267 subjects involved in the present study were analyzed within the study period. There were no cases involving OPLL identification prior to death, and no subjects presented with neurological symptoms of myelopathy. The incidence of cases involving high-density areas greater than 0.1 mm(2) in the PLL was 46.6 %, half of which revealed mature bone structures inside this area. Thus, the high-density areas comprised three types: a continuous posterior-annular fibrosus type (23 cases), an isolated posterior-annular fibrosus type (11 cases), and a posterior-vertebral type (29 cases). However, a positive correlation was observed between the proportion of high-density areas, age (Pearson r = 0.265, p < 0.01), and HbA1c (Pearson r = 0.294, p < 0.01). Histological examination confirmed that these high-density areas involved calcification with or without mature bone formation.

CONCLUSIONS

We evaluated minute foci of calcification with and without ossification in the PLL from 103 cadavers, generating the following observations: 1. Minute calcification foci greater than 0.1 mm(2) were observed in the PLL of 48 cases (46.6 %), half of which revealed mature bone structures inside this area (23.3 %). 2. The proportion of minute calcification foci observed in the present study was correlated with age and glucose tolerance, suggesting changes in the OPLL in the early stage. 3. Three different mechanisms of ossification were suggested: The two structures developed behind the disc might reflect the elongation of enthesis or rupture of annular fibrosus, while the remaining structure developed behind the vertebral body might reflect a dystrophic calcification-based bony metaplasia sequence.

Paravertebral ligament ossification in vitamin D-resistant rickets: incidence, clinical significance, and genetic evaluation

STUDY DESIGN

A retrospective observational study.

OBJECTIVE

The objective of this study was to analyze the cases of paravertebral ossification in vitamin D-resistant rickets (VDRR) and elucidate its incidence and clinical significance, and report specific genetic mutations uniquely associated with this phenomenon.

SUMMARY OF BACKGROUND DATA

Paravertebral ligament ossification has been described in VDRR in a few cases previously. However, supraspinous and interspinous ligament ossification has so far not been described to occur in association with VDRR. We reviewed 6 cases of paravertebral ligament ossification with the added feature of supraspinous and interspinous ligament calcification.

METHODS

Forty-four patients with clinical, radiological, and biochemical diagnoses of VDRR, who were positive for mutations in the PHEX gene, were screened for the presence of paravertebral ossification with plain radiographs and computed tomography/magnetic resonance imaging if necessary. This was correlated with the severity of disease, and we looked for specific genetic mutations.

RESULTS

Six patients had paravertebral ligament ossification, which included supraspinous and interspinous ligament ossification. These patients had a more severe systemic disease, with all patients requiring at least 1 surgery for deformity correction of the limbs, with a total of 10 surgical procedures performed in these 6 patients. c.1601C>T, c.1699C>T, c.1363G>T, and c.466_467insAC were the genetic mutations associated with these cases.

CONCLUSION

The spinal changes with paravertebral ligament ossification in VDRR were described in this study. Four different gene mutations related to the PHEX gene were detected in them. The presence of these changes was suggestive of a more severe systemic disease.

A patient with hypophosphatemic rickets and ossification of posterior longitudinal ligament caused by a novel homozygous mutation in ENPP1 gene

X-linked hypophosphatemic rickets/osteomalacia (XLH), autosomal dominant hypophosphatemic rickets/osteomalacia (ADHR) and autosomal recessive hypophosphatemic rickets/osteomalacia (ARHR1 or ARHR2) are hereditary fibroblast growth factor 23 (FGF23)-related hypophosphatemic rickets showing similar clinical features. We here show a patient with hypophosphatemic rickets and widespread ossification of posterior longitudinal ligament (OPLL). The proband is a 62-year-old female. Her parents are first cousins and showed no signs of rickets or osteomalacia. She showed hypophosphatemic rickets with elevated FGF23 level and had been clinically considered to be suffering from XLH. However, direct sequencing of all coding exons and exon-intron junctions of phosphate regulating gene with homologies to endopeptidases on the X chromosome (PHEX), FGF23 and dentin matrix protein 1 (DMP1) genes, responsible genes for XLH, ADHR and ARHR1, respectively, showed no mutation. A novel homozygous splice donor site mutation was found at the exon-intron junction of exon 21 of ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) gene responsible for ARHR2 (IVS21+1_3(GTA>CACC)). Subsequent analysis of mRNA revealed that this mutation caused skipping of exon 21 which created a premature stop codon in exon 22. These results indicate that genetic analysis is mandatory for the correct diagnosis of hereditary FGF23-related hypophosphatemic rickets. Because Enpp1 knockout mouse is a model of OPLL, this case also suggests that OPLL is associated with ARHR2.

Ossification of the ligamentum flavum: a unique report of a Hispanic woman

Ossification of the ligamentum flavum (OLF) is a disease of ectopic bone formation within the ligamentum flavum, which may result in mass effect and neurological compromise. The low thoracic region is the most common region of occurrence, and this is followed by the cervical, then lumbar, spine. The prevalence of OLF is significantly higher in the Japanese population compared with other nationalities and has a male preponderance. Ossification of the ligamentum flavum has been reported in association with the more common ligamentous pathological entities—ossification of the posterior longitudinal ligament and diffuse idiopathic skeletal hyperostosis. These latter two conditions have been linked to several metabolic processes, and a possible genetic basis has been hypothesized. Here, the authors present a unique case of OLF of the cervical spine in a patient with idiopathic hypercalcemia.

Phenotype presentation of hypophosphatemic rickets in adults

Hypophosphatemic rickets (HR) is a group of rare disorders caused by excessive renal phosphate wasting. The purpose of this cross-sectional study of 38 HR patients was to characterize the phenotype of adult HR patients. Moreover, skeletal and endodontic severity scores were defined to assess possible gender differences in disease severity in patients with genetically verified X-linked HR. Compared to normal reference data, i.e., z = 0, HR patients had significantly lower final height, with a mean difference in z-score of -1.9 (95% CI -2.4 to -1.4, P < 0.001). Compared to paired z-scores of final height, z-scores of leg length were significantly lower and those of sitting height were significantly higher (P < 0.001), resulting in disproportion as indicated by the significantly elevated sitting height ratio, mean difference in z-score of 2.6 (95% CI 2.1-3.1, P < 0.001). Z-scores of head circumference (median 1.4, range -0.4 to 5.5, P < 0.001) and z-scores of bone mineral density (BMD) of the lumbar spine (median 1.9, range -1.5 to 8.6, P < 0.001) were significantly elevated compared to normal reference data. The relative risk (RR) of fracture was reduced (RR = 0.34, 95% CI 0.20-0.57, P < 0.001). The skeletal severity score tended to be higher in males compared to females (P = 0.07), and no gender difference in endodontic severity was found. In conclusion, adult HR patients were characterized by short stature and were disproportioned. They had elevated BMD of the lumbar spine and a reduced risk of fractures. We found a tendency for males to be more severely affected than females.

Surgical treatment of multiple spinal canal stenoses associated with vitamin D-resistant rickets

We describe a 44-year-old woman who was diagnosed in childhood with vitamin D-resistant rickets, and who had paraparesis due to multiple spinal canal stenoses between C5 and L1 with ossification of the posterior longitudinal ligament and the yellow ligament. She was treated surgically with laminoplasty of the C2 through C7 levels and laminectomy from T8 through T11. Four months later, she underwent anterior fusion using an ilium graft by thoracotomy from the T12 to L1 levels. Six months after surgery, her symptoms improved. After 5 years, and with oral vitamin D, no progression of symptoms has been observed.

Tetraparesis secondary to cervical ossification of the posterior longitudinal ligament: case report

Ossification of the posterior longitudinal ligament (OPLL) is a rare cause of myelopathy in non-Oriental populations and relatively unrecognized by general practitioners. A case of an Afro-Brazilian 54-years-old woman presenting with tetraparesis due to cervical OPLL is presented. Emphasis is made for the inclusion of OPLL in the differential diagnosis of compressive cervical myelopathy.

Hormones and growth factors in the pathogenesis of spinal ligament ossification

Ossification of the spinal ligaments (OSL) is a pathologic condition that causes ectopic bone formation and subsequently results in various degrees of neurological deficit, but the etiology of OSL remains almost unknown. Some systemic hormones, such as 1,25-dihydroxyvitamin D, parathyroid hormone (PTH), insulin and leptin, and local growth factors, such as transforming growth factor-beta (TGF-beta), and bone morphogenetic protein (BMP), have been studied and are thought to be involved in the initiation and development of OSL. This review article summarizes these studies, delineates the possible mechanisms, and puts forward doubts and new questions. The related findings from studies of genes and target cells in the ligament of OSL are also discussed. Although these findings may be helpful in understanding the pathogenesis of OSL, much more research needs to be conducted in order to investigate the nature of OSL.

[Ossification of the common posterior longitudinal ligament of the spine and spinal cord compression in a patient from Senegal]

INTRODUCTION

Ossification of the posterior longitudinal ligament of the spine is a rare cause medullar compression.

OBSERVATION

A 50-year-old man from Senegal was referred with recent-onset mechanical lumbar pain with proximal motor deficiency of the lower limbs and somatosensory disorders. Magnetic resonance imaging revealed layered medullar compression, due to anterior cervical and mixed anterior and posterior thoracic ossification. Corticosteroid treatment led to regression of the pain and neurological disorders within a few days.

DISCUSSION

This case report of ossification of the posterior longitudinal ligament of the spine appears to be an idiopathic form corresponding to the "Japanese disease" initially thought to be limited to that population.