Hepatitis C-associated osteosclerosis: an unusual syndrome of acquired osteosclerosis in adults

The French multicentre elevated bone mass study: prevalence and causes

The purpose of this multicentric study was to evaluate the prevalence and causes of Elevated Bone Mass (EBM) in patients who underwent DXA scanning over a 10-year period. The prevalence of EBM was 1 in 100. The main causes of EBM were degenerative spine disorders and renal osteodystrophy.

INTRODUCTION

Reports of elevated bone mass (EBM) on routine dual energy X-Ray absorptiometry (DXA) scanning are not infrequent. However, epidemiological studies of EBM are few and definition thresholds are variable. The purpose of this French multicentric study was to evaluate the prevalence and causes of EBM in adult patients who underwent DXA scanning over a 10-year period.

METHODS

This multicentric, retrospective study was conducted in six French regional bone centres. DXA databases were initially searched for individuals with a bone mineral density (BMD) Z-score ≥ +4 at any site in the lumbar spine or hip from April 1st, 2008 to April 30st, 2018.

RESULTS

In all, 72,225 patients with at least one DXA scan were identified. Of these, 909 (322 men and 587 women) had a Z-score ≥ + 4, i.e. a prevalence of 1.26% [1.18-1.34%]. The DXA scan reports and imagery and medical records of the 909 EBM patients were reviewed and 936 causes were found. In 42 patients (4%), no cause could be determined due to unavailability of data. Artefactual causes of EBM were found in 752 patients (80%), in whom the predominant cause was degenerative disease of the spine (613 patients, 65%). Acquired causes of focal EBM-including Paget's disease (n = 7)-were found in 12 patients (1%), and acquired causes of generalized EBM-including renal osteodystrophy (n = 32), haematological disorders (n = 20) and hypoparathyroidism (n = 15)-in 84 patients (9%). Other causes were rare hereditary diseases and unknown EBM in 19 (2%) and 27 (3%) cases respectively.

CONCLUSIONS

The prevalence of EBM was approximately 1 in 100. These findings suggest that degenerative disease of the spine is the main cause of EBM, but that acquired or hereditary diseases are also causal factors.

Hepatitis C-Associated Osteosclerosis: Improvement After Treatment with Sofosbuvir, Daclatasvir, and Ibandronate: Case Report and Literature Review

Hepatitis C-associated osteosclerosis (HCAO) remains a rare condition despite the growing prevalence of hepatitis C virus (HCV) infection worldwide. Since the first case reported in 1992, this is the twenty-second case described. Patients with HCAO present with severe bone pain and elevated serum levels of bone markers, especially alkaline phosphatase (ALP), with increased bone density. We report here the case of a 59-year-old man with generalized bone pain and diagnosis of HCV infection. Biochemical tests showed elevated bone turnover markers, specifically, ALP, carboxy-terminal collagen crosslinks and osteocalcin. Imaging studies revealed generalized bone sclerosis. Bone mineral density was elevated in all validated sites. His clinical symptoms and bone-related findings were attributed to HCAO. He was sequentially treated with cholecalciferol, prednisone, sofosbuvir associated with daclatasvir and ibandronate, and progressed with undetectable viral load after HCV treatment, normalization of ALP levels after introduction of ibandronate, and pain improvement 1 year after discontinuation of the bisphosphonate. Bone pain complaints must be investigated in patients with HCV. HCAO is a differential diagnosis of increased bone mass.

Prevalence and causes of elevated bone mass

INTRODUCTION

Reports of elevated bone mass (EBM) on routine DXA scanning are not infrequent. However, epidemiological studies of EBM are few in number and definition thresholds variable. The purpose of this study was to assess the prevalence and causes of EBM in the general population referred to a single university hospital - catering for a population of 4 million inhabitants - for DXA scanning.

MATERIAL AND METHODS

DXA databases were initially searched for individuals with a bone mineral density (BMD) Z-score ≥+4 at any site in the lumbar spine or hip from April 1st, 2008 to April 30st, 2018. Two Hologic scanners were available at the Lille University Hospital (France). Prevalence of EBM was evaluated, as were causes associated with EBM.

RESULTS

At the lumbar spine, 18,229 bone density tests were performed in women and 10,209 in men. At the hip, 17,390 tests were performed in women and 9857 in men. The total number of patients who had at least one bone density test was 14,745, of which 64.2% were female. Of these 14,745 patients, 211 had a Z-score ≥+4 at any site, i.e. a prevalence of 1.43% [1.25%-1.64%]. The DXA scans and medical records of 92 men and 119 women with elevated BMD were reviewed to assess causes. An artefactual cause was found in 164 patients (75%) with EBM (mostly degenerative disease of the spine), and an acquired cause of focal EBM was found in only 2 patients, both of whom had sclerotic bone metastases from prostate cancer. An acquired cause of generalized EBM was found in 32 patients (15%), the vast majority of whom had renal osteodystrophy (n = 11), followed by hematological disorders (n = 9; e.g. myeloproliferative syndromes and mastocytosis) and diffuse bone metastases from solid cancer (n = 5). Of the remaining causes, rare hereditary diseases (e.g. osteopetrosis…) and unexplained EBM were found in 10 and 6 cases respectively.

CONCLUSION

The prevalence of EBM (Z-score ≥+4 at any site) was 1.43% [1.25%-1.64%]. In nearly all instances (97.1%) the explanation for EBM could be found in the medical record and through conventional investigations. This study suggests that the main cause of EBM is degenerative disease of the spine. Further studies are needed to differentiate artefactual EBM from hereditary or acquired EBM, and to investigate unexplained EBM. Genetic testing may prove useful in elucidating rare unknown causes.

High bone mass in adults

A finding of high bone mineral density (BMD) from routine dual-energy X-ray absorptiometry (DXA) screening is not uncommon. No consensus exists about the definition of high BMD, and T-score and/or Z-score cutoffs of ≥+2.5 or ≥+4 have been suggested. The many disorders that can result in high BMD are usually classified based on whether the BMD changes are focal vs. generalized or acquired vs. constitutional. In over half the cases, careful interpretation of the DXA report and images identifies the cause as an artefact (e.g., degenerative spinal disease, vascular calcifications, or syndesmophytes) or focal lesion (e.g., sclerotic bone metastasis or Paget's disease). Generalized acquired high BMD may be secondary to a diverse range of disorders such as fluorosis, diffuse bone sclerosis related to renal osteodystrophy, hematological diseases, and hepatitis C. Identification of the cause may require additional investigations such as imaging studies, serum tryptase assay, or serological tests for the hepatitis C virus. Finally, high BMD is a feature of many genetic diseases, most notably osteopetrosis and the disorders caused by mutations in the sclerostin gene SOST (sclerosing bone dysplasia and van Buchem disease) or in the LRP5 gene encoding the low-density lipoprotein receptor-related protein 5 (which is the Wnt co-receptor).

Hepatitis C-associated osteosclerosis: a new case with long-term follow-up and a review of the literature

Hepatitis C-associated osteosclerosis (HCAO) is an uncommon condition characterized by increased bone density, skeletal pain and elevated bone formation markers. Since 1992, only 17 cases have been reported. We herein describe the case of a 61-year-old woman affected by severe pain involving the lower limbs. The laboratory data showed an elevated serum alkaline phosphatase level, and the patient was found to be seropositive for hepatitis C virus infection. In addition, an X-ray skeleton survey showed marked cortical thickening of both femurs and tibias, and a whole-body bone scan revealed an increased cortical radionuclide uptake in the involved bones. These findings were consistent with a diagnosis of HCAO. In this report, we discuss the patient's clinical course over 16 years and, for the first time, show a normalized radioisotope uptake on bone scanning 10 years after the diagnosis.

An uncommon cause of acquired osteosclerosis in adults: hepatitis C-associated osteosclerosis

Hepatitis C-associated osteosclerosis (HCAO) is a rare sclerosing bone condition characterized by debilitating, predominantly lower extremity bone pain, accelerated bone turnover, and a generalized increase in histologically normal trabecular and cortical bone tissue. Herein we report the clinical presentation and imaging results of the 19th case of HCAO. Clinicians, particularly those caring for a population at risk for HCV infection, should be aware of this uncommon condition. The etio-pathogenesis of HCAO remains obscure but may bear important lessons in bone biology that could lead to new treatment options for osteoporosis.

Friend or foe: high bone mineral density on routine bone density scanning, a review of causes and management

A finding of high BMD on routine DXA scanning is not infrequent and most commonly reflects degenerative disease. However, BMD increases may also arise secondary to a range of underlying disorders affecting the skeleton. Although low BMD increases fracture risk, the converse may not hold for high BMD, since elevated BMD may occur in conditions where fracture risk is increased, unaffected or reduced. Here we outline a classification for the causes of raised BMD, based on identification of focal or generalized BMD changes, and discuss an approach to guide appropriate investigation by clinicians after careful interpretation of DXA scan findings within the context of the clinical history. We will also review the mild skeletal dysplasia associated with the currently unexplained high bone mass phenotype and discuss recent advances in osteoporosis therapies arising from improved understanding of rare inherited high BMD disorders.

A case of hepatitis C-associated osteosclerosis that was improved with the combination therapy of peginterferon alfa-2b and ribavirin

Hepatitis C-associated osteosclerosis (HCAO) is a rare disorder characterized by a marked increase in skeletal mass in patients who are infected with hepatitis C virus (HCV). The clinical presentation is an acquired deep bone pain with increased serum alkaline phosphatase (ALP) activity. We present a case of a patient with HCAO who was treated with antiviral therapy. A 42-year-old Japanese man presented with severe, stabbing pain in his lower limbs. He was diagnosed with hepatitis C secondary to intravenous drug use 20 years earlier. Serum biochemical studies revealed markedly elevated ALP activity and osteocalcin levels. Skeletal radiographs showed diffuse bony sclerosis with marked cortical thickening in the long bones. The bony findings and clinical symptoms were attributed to HCAO. The HCV RNA viral load was high and the genotype was 2a. The patient was treated with peginterferon alfa-2b and ribavirin for 24 weeks. After 24 weeks of the combination therapy, the patient had a sustained virological response and clinical remission of bone pain and a decrease in the level of serum ALP. In conclusion, HCAO was improved by the combination therapy of peginterferon alfa-2b and ribavirin when the patient achieved sustained virological response. It was confirmed that HCAO was one of the extrahepatic manifestations of HCV.

Hepatitis C-associated osteosclerosis: a case report

A 38-year-old man presented for evaluation of severe pain in his lower limbs of 16 months' duration. Radiographs showed diffuse bony sclerosis involving the axial and appendicular skeleton with marked cortical thickening in the diaphyseal regions of the long bones. Iliac crest biopsy revealed abundant sclerotic bone. The patient was diagnosed with hepatitis C secondary to intravenous drug use 20 years earlier, and the bony findings and clinical symptoms attributed to hepatitis C-associated osteosclerosis (HCAO). Little is known about the natural history of this disease; however, we discuss the patient's clinical course over 15 years.

Emerging pharmacologic therapies for osteoporosis

Osteoporotic fractures are an important public health problem, contributing substantially to morbidity and mortality in an ageing world population and consuming considerable health resources. Presently available pharmacologic therapies for prevention of fragility fractures are limited in scope, efficacy and acceptability to patients. Considerable efforts are being made to develop new, more effective treatments for osteoporosis, and to refine/optimize existing therapies. These novel treatments include an expanding array of drugs that primarily inhibit osteoclastic bone resorption: estrogenic compounds, bisphosphonates, inhibitors of receptor activator of NF-kappaB ligand signaling, cathepsin K inhibitors, c-src kinase inhibitors, integrin inhibitors and chloride channel inhibitors. The advent of intermittent parathyroid hormone (PTH) therapy has provided proof-of-principle that osteoblast-targeted (anabolic) agents can effectively prevent osteoporotic fractures, and is likely to be followed by the introduction of other therapies based on PTH (orally active PTH analogs, antagonists of the calcium sensing receptor, PTH-related peptide analogs) and/or agents that induce osteoblast anabolism by means of pathways involving key, recently identified, molecular targets (wnt-low-density lipoprotein receptor-related protein 5 signaling, sclerostin and matrix extracellular phosphoglycoprotein).

A case of hepatitis C-associated osteosclerosis in an elderly Japanese man

Hepatitis C-Associated Osteosclerosis (HCAO) is characterized by a marked increase in bone mass with deep bone pain. Since 1992, eleven cases of HCAO have been reported. This report describes an elderly Japanese man with HCAO, whose clinical course we followed for 3 years. A 68-year-old man developed pain in both pretibial regions in June 2000, and he had frequent episodic loss of muscular strength in his hands. He had recieved blood transfusion for a bleeding ulcer 43 years before and was seropositive for hepatitis C virus. His serum alkaline phosphatase (ALP) level was markedly increased, while his serum calcium was slightly decreased and serum phosphate was normal. Skeletal radiographs of the lower extremities showed a progressive increase in skeletal density, but did not show any apparent deformity. Administration of nonsteroidal anti-inflammatory drugs led to a reduction in bone pain. Treatment with vitamin D3 and calcium decreased the number of episodes of sudden muscular weakness and maintained serum calcium within the normal range. Three years after the onset of the disease, bone mineral density of his lumbar vertebrae and left hip rose from 0.963 g/cm2 to 1.096 g/cm2, and from 0.938 g/cm2 to 1.383 g/cm2, respectively. His serum ALP level decreased from 2889 to 277 IU/L (normal range: 104-338) and serum calcium normalized. These findings were accompanied by a decrease in bone pain. This case and previous reports suggest that the skeletal tissue of this disease appears to be of good quality.

Hyperbilirubinemia is not a major contributing factor to altered bone mineral density in patients with chronic liver disease

Reduced bone density is commonly encountered in patients with chronic liver disease. Prior studies have shown that unconjugated bilirubin inhibits osteoblast activity and function in vitro and in animal models of bone mineralization. To determine whether hyperbilirubinemia promotes the development of hepatic osteodystrophy, bone mineral density (BMD) was measured by dual energy X-ray absorptiometry in a cohort of 86 consecutive patients with chronic liver disease referred for liver transplant evaluation. The mean age of the study population was 52 years (range, 22-73), in which 52% were female and 90% were white. Average bone density values were significantly lower than expected for age, race, and sex, with Z-scores for the femoral neck and spine of -0.50 (95% confidence interval [CI] -0.63 to -0.37; p=0.0003) and -0.69 (95% CI -0.85 to -0.52; p=0.0001), respectively. Sixty-one subjects (71%) exhibited reduced BMD (T-score of femoral neck or spine<or=-1 standard deviation [SD] below the young-adult mean), and 18 subjects (21%) met criteria for osteoporosis (T-score<-2.5 SD). Stepwise logistic regression analyses identified significant associations between BMD and serum creatinine, alkaline phosphatase, age, and gender. On the other hand, neither unconjugated, nor conjugated, nor total serum bilirubin levels were found to predict diminished BMD. The lack of association between serum unconjugated bilirubin levels and bone mineralization was validated in hyperbilirubinemic Gunn rats, in which BMD and serum osteocalcin levels were no different than in wild-type rodents. In conclusion, the finding that serum bilirubin levels do not correlate with reduced BMD in patients with end-stage liver disease, and that chronic unconjugated hyperbilirubinemia does not lead to alterations in bone mineralization in Gunn rats, suggests that bilirubin is not a major contributing factor to hepatic osteodystrophy.

Hepatitis C-associated osteosclerosis (HCAO): report of a new case with involvement of the OPG/RANKL system

We report a new case of hepatitis C-associated osteosclerosis (HCAO). The clinical presentation of the patient was an acquired deep severe bone pain with increased serum bone alkaline phosphatase activity (up to 12 times the upper limit of normal), and generalized bone sclerosis, temporally related to the hepatitis C-virus (HCV) infection. We documented in this patient an increase of circulating osteoprotegerin (OPG), and a concentration of circulating receptor activator for nuclear factor-kB ligand (RANKL) below the lower limit of the reference range. The observed abnormalities of the OPG/RANKL system may contribute to the maintenance of the positive balance of bone remodeling that characterizes patients with HCAO.

Emerging and potential therapies for osteoporosis

Osteoporotic fractures are an important public health problem, contributing substantially to morbidity and mortality in an ageing world population and consuming considerable health resources. Currently available pharmacological therapies for prevention of fragility fractures are limited in scope, efficacy and acceptability to patients. Considerable efforts are being made to develop new, more effective treatments for osteoporosis and to refine/optimise existing therapies. These novel treatments include an expanding array of drugs that primarily inhibit osteoclastic bone resorption; oestrogenic compounds, bisphosphonates, inhibitors of receptor activator of nuclear factor-kappaB ligand signalling, cathepsin K inhibitors, c-src kinase inhibitors, integrin inhibitors and chloride channel inhibitors. The advent of intermittent para-thyroid hormone (PTH) therapy has provided proof-of-principle that osteo-blast-targeted (anabolic) agents can effectively prevent osteoporotic fractures, and is likely to be followed by the introduction of other therapies based upon PTH, such as orally active PTH analogues, antagonists of the calcium sensing receptor, PTH-related peptide analogues, and/or agents that induce osteoblast anabolism via pathways involving key, recently identified, molecular targets (wnt low-density lipoprotein receptor-related protein-5 signalling, sclerostin and matrix extracellular phosphoglycoprotein).

OPG/RANKL system imbalance in a case of hepatitis C-associated osteosclerosis: the pathogenetic key?

Hepatitis C-associated osteosclerosis (HCAO) is an impressive example of acquired diffuse osteosclerosis in adults, recently described in ten patients infected with hepatitis C virus (HCV). Its hallmark is a painful and generalized increase of bone mass. Bone biopsies show enhanced accretion rate, usually without histological abnormalities. The HCAO pathogenesis is hitherto unknown. HCV might induce a slow bone cell infection and the production of bone growth factors, such as insulin-like growth factors. Recently, receptor activator of nuclear factor-kappaB (RANK), its ligand (RANKL), and soluble decoy receptor osteoprotegerin (OPG) have been identified as a pivotal cytokine system in the bone remodeling control. We describe the 11th case of HCAO. Notably, the patient's bone biopsy showed the presence of a high number of OPG-positive osteoblasts, a slight increase of RANKL-positive stromal cells, and a dramatic reduction of the osteoclasts. Moreover, OPG serum levels were increased. These findings reported here for the first time are consistent with a pathogenetic role of the OPG/RANKL system imbalance in HCAO.

Distúrbios do eixo cálcio-PTH-vitamina D nas doenças hepáticas crônicas

Distúrbios no eixo cálcio-PTH-vitamina D são freqüentemente associados às doenças hepáticas crônicas (DHC). Já foi demonstrado que pacientes com DHC apresentam uma tendência à diminuição do cálcio e vitamina D, com aumento compensatório do PTH. Embora a diminuição da hidroxilação da vitamina D em 25 (OH) vitamina D fosse considerada o mecanismo principal destas alterações, estudos recentes vêm demonstrando que, mesmo nos estágios avançados de doença, o fígado ainda consegue manter níveis adequados de 25 (OH) vitamina D. Desta forma, outros fatores (ex: dieta inadequada, diminuição da exposição à luz solar) seriam os responsáveis pelas alterações no eixo cálcio-PTH-vitamina D. Além disso, o tratamento das DHC com glicocorticóides (fibrose cística) e ribavirina (Hepatite C) parece contribuir como agravante destes distúrbios. Por outro lado, parece ser a osteoporose, e não a osteomalácia ou o hiperparatireoidismo secundário, a principal alteração nas DHC. Assim, continua objeto de discussão o papel das alterações do eixo cálcio-PTH-vitamina D na osteodistrofia hepática.

Use of site-specific antibodies to characterize the circulating form of big insulin-like growth factor II in patients with hepatitis C-associated osteosclerosis

Hepatitis C-associated osteosclerosis (HCAO) is a rare syndrome of adult-onset osteosclerosis. An understanding of the factor(s) leading to the stimulation of bone formation in these patients may provide novel anabolic approaches for the treatment of osteoporosis. We have demonstrated that HCAO patients have a specific increase in circulating big IGF-II (IGF-IIE) and IGF-binding protein-2 (IGFBP-2) levels, and that IGF-IIE and IGFBP-2 circulate together in a bioavailable, 50-kDa complex. Patients with nonislet cell tumor hypoglycemia (NICTH) also have increased circulating IGF-IIE and IGFBP-2 levels. However, HCAO patients do not exhibit hypoglycemia, nor do NICTH patients exhibit obvious osteosclerosis. Thus, to better understand the reason(s) for the differing clinical manifestations of the IGF-IIE excess in the two syndromes, we characterized IGF-IIE in HCAO and NICTH sera using recently developed antibodies (Ab) recognizing either the full-length IGF-IIE 89-amino acid C-terminal extension peptide (IIE(138-156) Ab) or specific cleavage forms of IGF-IIE (IIE(78-88) Ab and IIE(89-101) Ab). The predominant IGF-IIE form in HCAO serum migrated on SDS-PAGE as a single band at approximately 18 kDa that reacted with the IIE(89-101) Ab. On the other hand, the predominant form in NICTH serum migrated as a doublet of 14 and 16 kDa that reacted with the IIE(78-88) Ab. There results are consistent with differential processing of the IGF-IIE precursor at predicted cleavage sites producing IGF-IIE(1-104) and IGF-IIE(1-88) in HCAO and NICTH, respectively. As these two forms may have differing biological activities and/or targeting properties, our findings may explain at least in part the different manifestations of IGF-IIE overproduction in the two syndromes.

Subcutaneous administration of insulin-like growth factor (IGF)-II/IGF binding protein-2 complex stimulates bone formation and prevents loss of bone mineral density in a rat model of disuse osteoporosis

Elevated serum levels of insulin-like growth factor binding protein-2 (IGFBP-2) and a precursor form of IGF-II are associated with marked increases in bone formation and skeletal mass in patients with hepatitis C-associated osteosclerosis. In vitro studies indicate that IGF-II in complex with IGFBP-2 has high affinity for bone matrix and is able to stimulate osteoblast proliferation. The purpose of this study was to determine the ability of the IGF-II/IGFBP-2 complex to increase bone mass in vivo. Osteopenia of the femur was induced by unilateral sciatic neurectomy in rats. At the time of surgery, 14-day osmotic minipumps containing vehicle or 2 microg IGF-II+9 microg IGFBP-2/100g body weight/day were implanted subcutaneously in the neck. Bone mineral density (BMD) measurements were taken the day of surgery and 14 days later using a PIXImus small animal densitometer. Neurectomy of the right hindlimb resulted in a 9% decrease in right femur BMD (P<0.05 vs. baseline). This loss in BMD was completely prevented by treatment with IGF-II/IGFBP-2. On the control limb, there was no loss of BMD over the 14 days and IGF-II/IGFBP-2 treatment resulted in a 9% increase in left femur BMD (P<0.05). Bone histomorphometry indicated increases in endocortical and cancellous bone formation rates and in trabecular thickness. These results demonstrate that short-term administration of the IGF-II/IGFBP-2 complex can prevent loss of BMD associated with disuse osteoporosis and stimulate bone formation in adult rats. Furthermore, they provide proof of concept for a novel anabolic approach to increasing bone mass in humans with osteoporosis.

Insulin-like growth factor system abnormalities in hepatitis C-associated osteosclerosis. Potential insights into increasing bone mass in adults

Hepatitis C-associated osteosclerosis (HCAO) is a rare disorder characterized by a marked increase in bone mass during adult life. Despite the rarity of HCAO, understanding the mediator(s) of the skeletal disease is of great interest. The IGFs-I and -II have potent anabolic effects on bone, and alterations in the IGFs and/or IGF-binding proteins (IGFBPs) could be responsible for the increase in bone formation in this disorder. Thus, we assayed sera from seven cases of HCAO for IGF-I, IGF-II, IGF-IIE (an IGF-II precursor), and IGFBPs. The distribution of the serum IGFs and IGFBPs between their ternary ( approximately 150 kD) and binary (approximately 50 kD) complexes was also determined to assess IGF bioavailability. HCAO patients had normal serum levels of IGF-I and -II, but had markedly elevated levels of IGF-IIE. Of the IGFBPs, an increase in IGFBP-2 was unique to these patients and was not found in control hepatitis C or hepatitis B patients. IGF-I and -II in sera from patients with HCAO were carried, as in the case of sera from control subjects, bound to IGFBP-3 in the approximately 150-kD complex, which is retained in the circulation. However, IGF-IIE was predominantly in the approximately 50-kD complex in association with IGFBP-2; this complex can cross the capillary barrier and access target tissues. In vitro, we found that IGF-II enhanced by over threefold IGFBP-2 binding to extracellular matrix produced by human osteoblasts and that in an extracellular matrix-rich environment, the IGF-II/IGFBP-2 complex was as effective as IGF-II alone in stimulating human osteoblast proliferation. Thus, IGFBP-2 may facilitate the targeting of IGFs, and in particular IGF-IIE, to skeletal tissue in HCAO patients, with a subsequent stimulation by IGFs of osteoblast function. Our findings in HCAO suggest a possible means to increase bone mass in patients with osteoporosis.