Clinical Evaluation of Melorheostosis in the Context of a Natural History Clinical Study

Melorheostosis (Leri's Disease): A Review

Melorheostosis is a noncancerous bone disease characterized by abnormal bone and soft tissue growth. Despite being identified almost a century ago, there are still many unknown aspects surrounding this condition. It can often be an incidental discovery, with patients experiencing associated pain and deformities. Diagnosis typically relies on X-rays, although not all cases exhibit the classic candle wax appearance. A new imaging sign known as the "dumpling on a plate sign" has been proposed for flat bones for both MRI and CT scans. A biopsy may be necessary in cases of uncertainty, as there is not a definitive histological feature. It is not uncommon for melorheostosis to be linked with other conditions, and a collaborative approach involving a multidisciplinary team should be considered. This condition should be considered in the differential diagnosis of sclerotic bone conditions. Management is generally aimed at symptom relief, either through conservative measures or surgical intervention.

Bone Material Properties in Bone Diseases Affecting Children

PURPOSE OF REVIEW

Metabolic and genetic bone disorders affect not only bone mass but often also the bone material, including degree of mineralization, matrix organization, and lacunar porosity. The quality of juvenile bone is moreover highly influenced by skeletal growth. This review aims to provide a compact summary of the present knowledge on the complex interplay between bone modeling and remodeling during skeletal growth and to alert the reader to the complexity of bone tissue characteristics in children with bone disorders.

RECENT FINDINGS

We describe cellular events together with the characteristics of the different tissues and organic matrix organization (cartilage, woven and lamellar bone) occurring during linear growth. Subsequently, we present typical alterations thereof in disorders leading to over-mineralized bone matrix compared to those associated with low or normal mineral content based on bone biopsy studies. Growth spurts or growth retardation might amplify or mask disease-related alterations in bone material, which makes the interpretation of bone tissue findings in children complex and challenging.

VEGF Secretion Drives Bone Formation in Classical MAP2K1+ Melorheostosis

Patients with classical melorheostosis exhibit exuberant bone overgrowth in the appendicular skeleton, resulting in pain and deformity with no known treatment. Most patients have somatic, mosaic mutations in MAP2K1 (encoding the MEK1 protein) in osteoblasts and overlying skin. As with most rare bone diseases, lack of affected tissue has limited the opportunity to understand how the mutation results in excess bone formation. The aim of this study was to create a cellular model to study melorheostosis. We obtained patient skin cells bearing the MAP2K1 mutation (affected cells), and along with isogenic control normal fibroblasts reprogrammed them using the Sendai virus method into induced pluripotent stem cells (iPSCs). Pluripotency was validated by marker staining and embryoid body formation. iPSCs were then differentiated to mesenchymal stem cells (iMSCs) and validated by flow cytometry. We confirmed retention of the MAP2K1 mutation in iMSCs with polymerase chain reaction (PCR) and confirmed elevated MEK1 activity by immunofluorescence staining. Mutation-bearing iMSCs showed significantly elevated vascular endothelial growth factor (VEGF) secretion, proliferation and collagen I and IV secretion. iMSCs were then differentiated into osteoblasts, which showed increased mineralization at 21 days and increased VEGF secretion at 14 and 21 days of differentiation. Administration of VEGF to unaffected iMSCs during osteogenic differentiation was sufficient to increase mineralization. Blockade of VEGF by bevacizumab reduced mineralization in iMSC-derived affected osteoblasts and in affected primary patient-derived osteoblasts. These data indicate that patient-derived induced pluripotent stem cells recreate the elevated MEK1 activity, increased mineralization, and increased proliferation seen in melorheostosis patients. The increased bone formation is driven, in part, by abundant VEGF secretion. Modifying the activity of VEGF (a known stimulator of osteoblastogenesis) represents a promising treatment pathway to explore. iPSCs may have wide applications to other rare bone diseases. © 2023 American Society for Bone and Mineral Research (ASBMR).

Occupational engagement, fatigue, and upper and lower extremity abilities in persons with melorheostosis

INTRODUCTION

Melorheostosis is a rare bone disorder with limited literature that describes the effect of this disease on functional and motor abilities. As part of a natural history study, four outcome measures were administered to better understand the burden this disease has on a person's ability to engage in basic and instrumental activities of daily living.

OBJECTIVE

To investigate the relationship between functional engagement, fatigue, and motor ability in patients with melorheostosis.

DESIGN

Cross-sectional data gathered from a longitudinal natural history observational study.

SETTING

Rehabilitation department within a single institution.

PARTICIPANTS

Forty-seven adult volunteers with melorheostosis were enrolled. Two participants were removed for failure to meet diagnosis eligibility. Thirty patients had lower extremity (LE) osteosclerotic bone lesions, 14 had upper extremity (UE) lesions, and one had lesions in both UEs and LEs.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Activity Card Sort, Second Edition (ACS); Multi-Dimensional Fatigue Inventory; Lower Extremity Functional Scale; Upper Extremity Functional Index.

RESULTS

On the ACS, high-demand leisure (HDL) activities were the least retained (p < .001). Of the activities rated most important, HDL activities were the most likely to have been given up (27%). General fatigue (μ = 11.8) and physical fatigue (μ = 11.0) were the two most limiting fatigue constructs. There were moderate negative correlations with HDL activities compared to physical fatigue (r = -0.524, p < .001) and reduced activity fatigue (r = -0.58, p = .001). LE lesions had a large effect on completing LE tasks (d = 0.95) and UE lesions had a medium effect on completing tasks involving the UE (d = 0.69).

CONCLUSIONS

Patients with melorheostosis experience fatigue and low engagement in HDL activities. The results of this study underscore the importance of acknowledging activity domain, fatigue constructs, and lesion location to support and provide targeted evidence-based rehabilitative therapy.

CLINICAL TRIAL REGISTRATION NUMBER

NCT02504879.

Fibroblasts from Patients with Melorheostosis Promote Angiogenesis in Healthy Endothelial Cells through Secreted Factors

Melorheostosis is a rare sclerosing bone disease with associated vascular abnormalities in skin and bone, which is caused by somatic mosaic single nucleotide variations in the MAP2K1 gene, which encodes MAPK/extracellular signal‒regulated kinase (ERK) kinase 1. However, disease pathogenesis is poorly understood. Using patient-derived cells, we found that affected skin fibroblasts carrying the single nucleotide variations have increased activation of ERK1/2, which results in increased expression and secretion of proangiogenic factors, including VEGF. VEGF secretion was strongly reduced in affected cells after treatment with MAPK/ERK kinase 1 inhibitor trametinib. Treatment of healthy endothelial cells on matrigel with conditioned medium from affected fibroblasts induces the adoption of a proangiogenic phenotype. Direct coculture of fibroblasts and endothelial cells further shows that both secreted factors and extracellular matrix are capable of inducing a proangiogenic phenotype in healthy endothelial cells. Blocking VEGF with bevacizumab reduces the proangiogenic effect of affected fibroblasts in both the matrigel and direct coculture angiogenesis models, indicating that elevated VEGF secretion is a key mediator of increased angiogenesis in melorheostosis tissue. In conclusion, this work identifies the role of several important molecular mediators in the pathogenesis of melorheostosis, including MAPK/ERK kinase 1, phosphorylated ERK1/2, and VEGF, all of which have clinically available pharmacologic inhibitors, which could be further explored as therapeutic targets.

18F-Sodium Fluoride PET as a Diagnostic Modality for Metabolic, Autoimmune, and Osteogenic Bone Disorders: Cellular Mechanisms and Clinical Applications

In a healthy body, homeostatic actions of osteoclasts and osteoblasts maintain the integrity of the skeletal system. When cellular activities of osteoclasts and osteoblasts become abnormal, pathological bone conditions, such as osteoporosis, can occur. Traditional imaging modalities, such as radiographs, are insensitive to the early cellular changes that precede gross pathological findings, often leading to delayed disease diagnoses and suboptimal therapeutic strategies. ¹⁸F-sodium fluoride (¹⁸F-NaF)-positron emission tomography (PET) is an emerging imaging modality with the potential for early diagnosis and monitoring of bone diseases through the detection of subtle metabolic changes. Specifically, the dissociated ¹⁸F^- is incorporated into hydroxyapatite, and its uptake reflects osteoblastic activity and bone perfusion, allowing for the quantification of bone turnover. While ¹⁸F-NaF-PET has traditionally been used to detect metastatic bone disease, recent literature corroborates the use of ¹⁸F-NaF-PET in benign osseous conditions as well. In this review, we discuss the cellular mechanisms of ¹⁸F-NaF-PET and examine recent findings on its clinical application in diverse metabolic, autoimmune, and osteogenic bone disorders.

Cross-Sectional Imaging Useful in Melorheostosis

Melorheostosis is a rare disease of bone overgrowth that is primarily diagnosed based on imaging studies. Recently, the association of different radiological patterns of the disease with distinct genetic cause was reported. Several case reports have described the radiological findings in patients with melorheostosis. However, the added value of cross‐sectional imaging with CT and MRI beyond X‐rays has not been investigated. The aim of the current study was to investigate this existing gap in knowledge. Forty patients with melorheostosis seen at the National Institute of Health Clinical Center were included in the study, and all their imaging studies were analyzed. The sequence of interpretation was X‐ray followed by CT and then MRI. CT images were extracted from whole‐body 18F‐sodium fluoride positron emission tomography/CT studies. The information from CT reclassified the initial X‐rays based radiological pattern in 13 patients. Additionally, CT comprehensively identified joint involvement and disease extent. In 76% of patients (n = 29) who underwent MRI, additional findings were noted, ranging from soft tissue edema to identification of soft tissue masses and incidental findings. MRI did not provide additional information on skeletal lesions beyond CT scans. However, it revealed the extension of soft tissue ossification into ischiofemoral space in four patients who complained of deep gluteal pain consistent with ischiofemoral impingement syndrome. In addition, MRI revealed soft tissue edema in 20 patients, 9 of whom had bone marrow edema and periosteal edema in the tibias consistent with shin splints. These findings suggest that select patients with melorheostosis should be evaluated with both CT and MRI, particularly patients in whom the distribution of pain does not correlate with the anatomic location of the disease in plain radiographs. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.

A Rare Case of Melorheostosis in the Hand of a Saudi Woman

Melorheostosis is a very rare bone dysplasia, especially in the hand. Most cases were diagnosed incidentally, with the lower limbs being the most affected. This is the first Saudi woman with hand melorheostosis. A 33-year-old Saudi female had mild to moderate right-hand pain that started six years ago. Hand examination showed a full range of motion and full hand grip, and there was no tenderness upon palpation. Plain X-ray, unenhanced CT scan, and MRI of the hand showed an appearance resembling dripping candle wax as melorheostosis. The bone scan showed a nonvascular and nonacute lesion. An unenhanced CT scan demonstrated cortical and endosteal hyperostosis involving the proximal, middle, and distal third and fourth phalanges. Multi-sequential MRI of the hand demonstrated cortical hyperostosis involving the ulnar and radial aspect of the right fourth proximal, middle, and distal phalanges. Features in the X-ray, CT scan, bone scan, and MRI confirmed a diagnosis of melorheostosis with associated flexor tenosynovitis.