Diagnosis and management of tumor-induced osteomalacia: a single center experience

PURPOSE

The aim of this study is to review the clinical and laboratory characteristics, diagnostic and treatment modalities of tumor-induced osteomalacia (TIO) cases managed in a single center.

MATERIAL METHODS

Demographic and clinical features, biochemical findings, diagnostic procedures, treatment modalities, and outcomes of nine patients who had the diagnosis of TIO were reviewed retrospectively.

RESULTS

Mean age of the study group (F/M: 4/5) was 45.8 ± 10.8 years, and mean time from the onset of symptoms to diagnosis was 4.7 ± 2.8 years. The clinical manifestations were muscle weakness and difficulty in walking (8/9), hip pain (3/9), multiple fractures (2/9), stress fracture (2/9). Mean plasma phosphorus concentration was 1.28 ± 0.4 mg/dl at presentation. We performed radionuclide imaging modalities (18F-FDG PET/CT, Ga68-DOTATATE PET/CT, octreotide scintigraphy) in seven of nine patients, and tumor was detected in all. Lower extremity (n = 6; %67), head region (n = 2; %22) and thorax (n = 1; %11) were the tumor locations of our cases. Eight patients underwent surgery and remission was achieved postoperatively in all of the operated patients and plasma phosphorus level normalized in 4 ± 2 days. Pathological examination revealed mesenchymal tumors with different subtypes. Recurrence occurred in three patients at 13 ± 10.5 months after the first surgery. Two patients were reoperated and radiotherapy was also performed in one of them.

CONCLUSION

Hypophosphatemia necessitates careful evaluation for the etiology. TIO is one of the important causes of adult-onset hypophosphatemic osteomalacia. Diagnosis of TIO is essential because the laboratory and clinical findings resolve after appropriate treatment.

Challenges in the management of tumor-induced osteomalacia (TIO)

Tumor-induced osteomalacia (TIO), also known as oncogenic osteomalacia, is a rare acquired paraneoplastic disease, which is challenging to diagnose and treat. TIO is characterized by hypophosphatemia resulting from excess levels of tumor-secreted fibroblast growth factor 23 (FGF23), one of the key physiological regulators of phosphate metabolism. Elevated FGF23 results in renal phosphate wasting and compromised vitamin D activation, ultimately resulting in osteomalacia. Patients typically present with progressive and non-specific symptoms, including bone pain, multiple pathological fractures, and progressive muscle weakness. Diagnosis is often delayed or missed due to the non-specific nature of complaints and lack of disease awareness. Additionally, the disease-causing tumour is often difficult to detect and localize because they are often small, lack localizing symptoms and signs, and dwell in widely variable anatomical locations. Measuring serum/urine phosphate should be an inherent diagnostic component when assessing otherwise unexplained osteomalacia, fractures and weakness. In cases of hypophosphatemia with inappropriate (sustained) phosphaturia and inappropriately normal or frankly low 1,25-dihydroxy vitamin D, differentiation of the potential causes of renal phosphate wasting should include measurement of FGF23, and TIO should be considered. While patients experience severe disability without treatment, complete excision of the tumour is typically curative and results in a dramatic reversal of symptoms. Two additional key current unmet needs in optimizing TIO management are: (1 and 2) the considerable delay in diagnosis and consequent delay between the onset of symptoms and surgical resection; and (2) alternative management. These may be addressed by raising awareness of TIO, and taking into consideration the accessibility and variability of different healthcare infrastructures. By recognizing the challenges associated with the diagnosis and treatment of TIO and by applying a stepwise approach with clear clinical practice guidelines, patient care and outcomes will be improved in the future.

FGF23-related hypophosphatemic rickets/osteomalacia: diagnosis and new treatment

FGF23 is a phosphaturic hormone produced by bone. FGF23 reduces serum phosphate by suppressing proximal tubular phosphate reabsorption and intestinal phosphate absorption. After the identification of FGF23, several kinds of hypophosphatemic rickets/osteomalacia such as X-linked hypophosphatemia (XLH) and tumor-induced osteomalacia (TIO) have been shown to be caused by excessive actions of FGF23. Circulatory FGF23 is high in patients with these hypophosphatemic diseases while FGF23 is rather low in those with chronic hypophosphatemia from other causes such as vitamin D deficiency. These results indicate that FGF23 measurement is useful for the differential diagnosis of hypophosphatemia. Chemiluminescent enzyme immunoassay for FGF23 has been approved for clinical use in Japan. The first choice treatment for patients with TIO is complete removal of responsible tumors. However, it is not always possible to find and completely remove responsible tumors. Phosphate and active vitamin D have been used for patients with hypophosphatemic diseases caused by excessive actions of FGF23 including TIO patients with unresectable tumors. However, these medications have limited effects and several adverse events. The inhibition of excessive FGF23 actions has been considered to be a novel therapy for these hypophosphatemic diseases. Human MAB for FGF23, burosumab, has been shown to improve biochemical abnormalities, roentgenological signs of rickets, growth, fracture healing and impaired mineralization in patients with XLH. Burosumab has been approved in several countries including Europe, North America and Japan. Long-term effects of burosumab need to be addressed in future studies.

FGF23 and Associated Disorders of Phosphate Wasting

Fibroblast growth factor 23 (FGF23), one of the endocrine fibroblast growth factors, is a principal regulator in the maintenance of serum phosphorus concentration. Binding to its cofactor αKlotho and a fibroblast growth factor receptor is essential for its activity. Its regulation and interaction with other factors in the bone-parathyroid-kidney axis is complex. FGF23 reduces serum phosphorus concentration through decreased reabsorption of phosphorus in the kidney and by decreasing 1,25 dihydroxyvitamin D (1,25(OH)2D) concentrations. Various FGF23-mediated disorders of renal phosphate wasting share similar clinical and biochemical features. The most common of these is X-linked hypophosphatemia (XLH). Additional disorders of FGF23 excess include autosomal dominant hypophosphatemic rickets, autosomal recessive hypophosphatemic rickets, fibrous dysplasia, and tumor-induced osteomalacia. Treatment is challenging, requiring careful monitoring and titration of dosages to optimize effectiveness and to balance side effects. Conventional therapy for XLH and other disorders of FGF23-mediated hypophosphatemia involves multiple daily doses of oral phosphate salts and active vitamin D analogs, such as calcitriol or alfacalcidol. Additional treatments may be used to help address side effects of conventional therapy such as thiazides to address hypercalciuria or nephrocalcinosis, and calcimimetics to manage hyperparathyroidism. The recent development and approval of an anti-FGF23 antibody, burosumab, for use in XLH provides a novel treatment option.

[Rickets/Osteomalacia. Anti-FGF23 antibody therapy in patients with FGF23-related hypophosphatemic rickets and osteomalacia.]

Fibroblast growth factor 23(FGF23)is a phosphaturic hormone, and its excess causes several kinds of congenital and acquired hypophosphatemic diseases. A combination of oral active vitamin D3 and phosphate salt is the current standard therapy for patients with FGF23-related hypophosphatemic rickets and osteomalacia. However, these medications may cause long-term complications, such as secondary hyperparathyroidism and chronic kidney disease. Therefore, an anti-FGF23 neutralizing antibody that blocks FGF23 activity has been produced. X-linked hypophosphatemic rickets(XLHR)is the most prevalent form of hereditary FGF23-related hypophosphatemia. The safety and efficacy of a human anti-FGF23 antibody, KRN23 or burosumab, has been confirmed in adults and children with XLHR. Moreover, Burosumab is being tested as a potential treatment for patients with tumor-induced osteomalacia(TIO), which is the most prevalent form of acquired FGF23-related hypophosphatemia.

Osteomalacia induced by long-term low-dose adefovir dipivoxil: Clinical characteristics and genetic predictors

CONTEXT

Adefovir dipivoxil (ADV) was an important cause of adult-onset hypophosphatemic osteomalacia. However, its clinical characteristics and mechanisms have not been well defined.

OBJECTIVE

The objective of the study was to summarize the clinical characteristics of ADV-induced osteomalacia and to explore the association between ADV-associated tubulopathy and polymorphisms in genes encoding drug transporters.

DESIGN, SETTING, PATIENTS, AND MAIN OUTCOME MEASURE

Seventy-six affected patients were clinically studied. The SLC22A6 and ABCC2 genes were screened and compared with healthy people from the HapMap.

RESULTS

Hypophosphatemia, high serum alkaline phosphatase (ALP) levels, hypouricemia, nondiabetic glycosuria, proteinuria, metabolic acidosis and high bone turnover markers were the main metabolic characteristics. Fractures and pseudofractures occurred in 39 patients. Stopping ADV administration, supplementing calcitriol and calcium was effective during the follow-up period. Single SNP analysis revealed a higher percentage of the G/A genotype at c.2934 in exon 22 of the ABCC2 gene (rs3740070) in patients than in healthy people (12% [7 of 58 patients] vs. 0% [0 of 45 patients]; P=0.017), while there was no subject with homozygosity for the A allele at c.2934.

CONCLUSIONS

ADV can be nephrotoxic at a conventional dosage. The G/A genotype at c.2934 of the ABCC2 gene may be a predictor of patients at greater risk for developing ADV-associated tubulopathy. Larger case-control studies are needed to further verify this finding.

Global Consensus Recommendations on Prevention and Management of Nutritional Rickets

BACKGROUND

Vitamin D and calcium deficiencies are common worldwide, causing nutritional rickets and osteomalacia, which have a major impact on health, growth, and development of infants, children, and adolescents; the consequences can be lethal or can last into adulthood. The goals of this evidence-based consensus document are to provide health care professionals with guidance for prevention, diagnosis, and management of nutritional rickets and to provide policy makers with a framework to work toward its eradication.

EVIDENCE

A systematic literature search examining the definition, diagnosis, treatment, and prevention of nutritional rickets in children was conducted. Evidence-based recommendations were developed using the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) system that describe the strength of the recommendation and the quality of supporting evidence.

PROCESS

Thirty-three nominated experts in pediatric endocrinology, pediatrics, nutrition, epidemiology, public health, and health economics evaluated the evidence on specific questions within five working groups. The consensus group, representing 11 international scientific organizations, participated in a multiday conference in May 2014 to reach a global evidence-based consensus.

RESULTS

This consensus document defines nutritional rickets and its diagnostic criteria and describes the clinical management of rickets and osteomalacia. Risk factors, particularly in mothers and infants, are ranked, and specific prevention recommendations including food fortification and supplementation are offered for both the clinical and public health contexts.

CONCLUSION

Rickets, osteomalacia, and vitamin D and calcium deficiencies are preventable global public health problems in infants, children, and adolescents. Implementation of international rickets prevention programs, including supplementation and food fortification, is urgently required.

Urinary β-2 Microglobulin Levels Sensitively Altered in an Osteomalacia Patient Receiving Add-on Adefovir Dipivoxil Therapy for Hepatitis B Virus Infection

Adefovir dipivoxil (ADV) is effective for hepatitis B virus (HBV) infection; however, ADV may provoke renal injury resulting in osteomalacia, and this side effect is seldom recognized until bone fractures emerge. We herein present a 66-year-old woman with HBV infection who received ADV for 6 years. Although she exhibited no sign of bone fractures, her urinary β-2 microglobulin (β2MG) level increased to 83,837 μg/L and scintigraphy revealed minimal fractures of the third rib. ADV was subsequently reduced and her urinary β2MG rapidly fell to 3,637 μg/L. Conversely, her urinary N-acetyl-β-D-glucosaminidase, and serum phosphate, alkaline phosphatase levels did not respond.

[My Back is Still Hurting!]

We present the case of a 39-year-old man who reported to the primary care physician for low back pain. Pain persisted despite extensive assessment and therapy. During the course, bilateral femoral neck fractures occurred and due to multiple enrichments in scintigraphy chronic multifocal (sterile) osteomyelitis was suspected. In the further follow-up the appropriate diagnosis of osteomalacia was established in bone biopsy and adequate treatment with Vitamin D was initiated. During therapy, the patient was free of pain or discomfort.

Pathogenesis and diagnostic criteria for rickets and osteomalacia - proposal by an expert panel supported by Ministry of Health, Labour and Welfare, Japan, The Japanese Society for Bone and Mineral Research and The Japan Endocrine Society

Rickets and osteomalacia are diseases characterized by impaired mineralization of bone matrix. Recent investigations revealed that the causes for rickets and osteomalacia are quite variable. While these diseases can severely impair the quality of life of the affected patients, rickets and osteomalacia can be completely cured or at least respond to treatment when properly diagnosed and treated according to the specific causes. On the other hand, there are no standard criteria to diagnose rickets or osteomalacia nationally and internationally. Therefore, we summarize the definition and pathogenesis of rickets and osteomalacia, and propose the diagnostic criteria and a flowchart for the differential diagnosis of various causes for these diseases. We hope that these criteria and flowchart are clinically useful for the proper diagnosis and management of patients with these diseases.

A Practical Approach to Vitamin D Deficiency and Rickets

Rickets is a condition in which there is failure of the normal mineralisation (osteomalacia) of growing bone. Whilst osteomalacia may be present in adults, rickets cannot occur. It is generally caused by a lack of mineral supply, which can either occur as a result of the deficiency of calcium (calciopaenic rickets, now known as parathyroid hormone-dependent rickets) or of phosphate (phosphopaenic rickets, now called FGF23-dependent rickets). Renal disorders may also interfere with the process of mineralisation and cause rickets. Only parathyroid hormone-dependent rickets and distal renal tubular disorders will be discussed in this chapter. The most common cause of rickets is still vitamin D deficiency, which is also responsible for other problems. Disorders of vitamin D metabolism or responsiveness may also cause similar issues. Distal renal tubular acidosis may also be caused by a variety of metabolic errors similar to those of osteoclasts. One form of distal renal tubular acidosis also causes a type of osteopetrosis. This chapter describes these conditions in detail and sets out a logical approach for treatment.

[Metabolic bone and joint diseases]

Metabolic bone and joint diseases in adults include osteomalacia, rheumatoid arthritis, gouty arthritis. Recently, the newest molecular biology procedures and the clinical observation studies can produce good results for understanding of these diseases. From this perspective, the author introduced updated information of the pathophysiology, the latest diagnostic criteria and the therapy of these diseases.

Osteodystrophy in chronic liver diseases

Osteoporosis and osteomalacia are, to date, among the most common metabolic diseases in the world. Lately, an association between metabolic bone diseases and chronic liver disease has been increasingly reported, inducing many authors to create a new nosographic entity known as 'hepatic osteodystrophy.' The importance of such a condition is further increased by the morbidity of these two diseases, which greatly reduce the quality of life because of frequent fractures, especially vertebral and femoral neck ones. For this reason, early identification of high-risk patients should be routinely performed by measuring bone mass density. The explanation for the association between bone diseases and chronic liver disease is still uncertain, and involves many factors: from hypogonadism to use of corticosteroid drugs, from genetic factors to interferon therapy. To date, few studies have been conducted, and all with a small number of patients to establish definitive conclusions about the possible treatment, but some evidence is beginning to emerge about the safety and efficacy of bisphosphonates.

Osteomalacia and insufficiency fracture in a hemodialysis patient with autosomal dominant polycystic kidney disease

A 61-year-old Japanese woman on hemodialysis with autosomal dominant polycystic kidney disease (ADPKD) was admitted to the hospital with gluteal pain. Radiographs demonstrated a fracture of the left pubis. The serum 1,25(OH)(2)-vitamin D and 25(OH)-vitamin D levels were low. A biopsy of the right iliac crest disclosed osteomalacia. Active vitamin D sterol was administered in conjunction with dietary modification. Her gluteal pain was resolved three years later, and healing of the fracture was confirmed by radiology. This case emphasizes that vitamin D deficiency and malnutrition can cause osteomalacia in dialysis patients, even if calcium (Ca) and phosphate (P) levels are controlled by calcium carbonate.

Regulation of bone-renal mineral and energy metabolism: the PHEX, FGF23, DMP1, MEPE ASARM pathway

More than 300 million years ago, vertebrates emerged from the vast oceans to conquer gravity and the dry land. With this transition, new adaptations occurred that included ingenious changes in reproduction, waste secretion, and bone physiology. One new innovation, the egg shell, contained an ancestral protein (ovocleidin-116) that likely first appeared with the dinosaurs and was preserved through the theropod lineage in modern birds and reptiles. Ovocleidin-116 is an avian homolog of matrix extracellular phosphoglycoprotein (MEPE) and belongs to a group of proteins called short integrin-binding ligand-interacting glycoproteins (SIBLINGs). These proteins are all localized to a defined region on chromosome 5q in mice and chromosome 4q in humans. A unifying feature of SIBLING proteins is an acidic serine aspartate-rich MEPE-associated motif (ASARM). Recent research has shown that the ASARM motif and the released ASARM peptide have regulatory roles in mineralization (bone and teeth), phosphate regulation, vascularization, soft-tissue calcification, osteoclastogenesis, mechanotransduction, and fat energy metabolism. The MEPE ASARM motif and peptide are physiological substrates for PHEX, a zinc metalloendopeptidase. Defects in PHEX are responsible for X-linked hypophosphatemic rickets (HYP). There is evidence that PHEX interacts with another ASARM motif containing SIBLING protein, dentin matrix protein-1 (DMP1). DMP1 mutations cause bone and renal defects that are identical with the defects caused by a loss of PHEX function. This results in autosomal recessive hypophosphatemic rickets (ARHR). In both HYP and ARHR, increased FGF23 expression plays a major role in the disease and in autosomal dominant hypophosphatemic rickets (ADHR), FGF23 half-life is increased by activating mutations. ASARM peptide administration in vitro and in vivo also induces increased FGF23 expression. FGF23 is a member of the fibroblast growth factor (FGF) family of cytokines, which surfaced 500 million years ago with the boney fish (i.e., teleosts) that do not contain SIBLING proteins. In terrestrial vertebrates, FGF23, like SIBLING proteins, is expressed in the osteocyte. The boney fish, however, are an-osteocytic, so a physiological bone-renal link with FGF23 and the SIBLINGs was cemented when life ventured from the oceans to the land during the Triassic period, approximately 300 million years ago. This link has been revealed by recent research that indicates a competitive displacement of a PHEX-DMP1 interaction by an ASARM peptide that leads to increased FGF23 expression. This review discusses the new discoveries that reveal a novel PHEX, DMP1, MEPE, ASARM peptide, and FGF23 bone-renal pathway. This pathway impacts not only bone formation, bone-renal mineralization, and renal phosphate homeostasis but also energy metabolism. The study of this new pathway is relevant for developing therapies for several diseases: bone-teeth mineral loss disorders, renal osteodystrophy, chronic kidney disease and bone mineralization disorders (CKD-MBD), end-stage renal diseases, ectopic arterial-calcification, cardiovascular disease renal calcification, diabetes, and obesity.

[Hypophosphatemia and tumor-induced osteomalacia]

In this article, we will discuss about hypophosphatemia due to tumor-induced osteomalacia. This disease is characterized by severe muscular and articular tenderness inducing profound walking limitation. Clinical chemistry results show severe hypophosphatemia due to hyperphosphaturia. Fibroblast growth factor 23 (FGF-23) is abnormally high. Physiological role of FGF-23 is examined. We also consider the pathophysiology of tumor induced osteomalacia, the use of different investigations to localize the tumor and therapies available to treat this rare disease.

Tumor-induced osteomalacia

Tumor-induced osteomalacia (TIO) is a rare and fascinating paraneoplastic syndrome in which patients present with bone pain, fractures, and muscle weakness. The cause is high blood levels of the recently identified phosphate and vitamin D-regulating hormone, fibroblast growth factor 23 (FGF23). In TIO, FGF23 is secreted by mesenchymal tumors that are usually benign, but are typically very small and difficult to locate. FGF23 acts primarily at the renal tubule and impairs phosphate reabsorption and 1α-hydroxylation of 25-hydroxyvitamin D, leading to hypophosphatemia and low levels of 1,25-dihydroxy vitamin D. A step-wise approach utilizing functional imaging (F-18 fluorodeoxyglucose positron emission tomography and octreotide scintigraphy) followed by anatomical imaging (computed tomography and/or magnetic resonance imaging), and, if needed, selective venous sampling with measurement of FGF23 is usually successful in locating the tumors. For tumors that cannot be located, medical treatment with phosphate supplements and active vitamin D (calcitriol or alphacalcidiol) is usually successful; however, the medical regimen can be cumbersome and associated with complications. This review summarizes the current understanding of the pathophysiology of the disease and provides guidance in evaluating and treating these patients. Novel imaging modalities and medical treatments, which hold promise for the future, are also reviewed.

Bone mineral disorder resulting from secondary distal renal tubular acidosis due to overlap syndrome (mixed connective tissue disorder) associated with coronary artery disease

A 35 year old female presented with chronic bone mineral disorder which was due to secondary renal tubular acidosis--type 1 (RTA1). Serologically there was definite evidence of overlap syndrome (mixed connective tissue disease--M.C.T.D.), which was the cause for RTA1. During hospitalization she developed coronary artery thrombosis.

[Progressive course of hypophosphatemic osteomalacia during 25-year follow up]

INTRODUCTION

Hypophosphatemic osteomalacia is defined as mineralization of the newly formed bone matrix (osteoids) in adults as a consequence of the phosphate deficiency.

CASE REPORT

A female from Belgrade, aged 62 years fell ill in 1982. when she was 36. She first felt pains in bones associated with chronic fatigue. In 1986. during her hospitalization the presence of neoplastic hematologic, endocrinologic, urogenital and gastroenterologic system deseases was excluded. Hypophosphatemic osteomalacia was diagnosed on the basis of the history, clinical presentation, physical examination, radiologic finding and laboratory analyses (lower serum phosphorus level). The initial therapy included a mixture of phosphates, vitamin D and calcium. The doses were several times corrected over the following four years. In 1990 she had a mild clinical deterioration requiring recorrection of the mentioned therapy. In 1993 bilateral femoral neck fractures occurred and subsequent osetosynthe as was performed. The disease had a progressive character in spite of the administered drug therapy so that multiple fractures occurred in 2000. During the last hospitalization in 2008. neither new pseudo fractures nor fractures were found although biochemical profile of the hypophosphatemic osteomalacia was still present.

CONCLUSION

The aim of this study was to emphasize the complexity in both diagnostic and therapeutic approach in the case of hypophosphatemic osteomalacia. In the presented case the patient showed a complicated and progressive course. In our opinion such course was a consequence of impossible etiologic treatment and discontinued therapy

[Paraneoplastic endocrine syndromes: diagnosis and management]

Paraneoplastic endocrine syndromes define a group of secondary signs and symptoms associated to a neoplasia, independently from the location of the primary tumor or its metastases. Paraneoplastic or ectopic endocrine syndromes usually result from aberrant hormone precursors or hormone-like substances by tumours. Knowledge of paraneoplastic endocrine complications is important both for the early diagnosis of neoplasia and the prognosis of the patient. In this review we discuss almost all reported paraneoplastic endocrine syndromes. We analyze their prevalence, etiology, laboratory diagnosis and treatment.

[Metabolic bone diseases]

Osteomalacia is caused by impaired vitamin D receptor (VDR) signaling, calcium deficiency, and altered bone mineralization. This can be due to insufficient sunlight exposure, malabsorption, reduced D hormone activation in chronic kidney disease, and rare alterations of VDR signaling and phosphate metabolism. Leading symptoms are bone pain, muscular cramps, and increased incidence of falls in the elderly. The adequate respective countermeasures are to optimize the daily intake of calcium and vitamin D3 and to replace active D hormone and phosphate if deficient. Osteoporosis is characterized by bone fragility fractures upon minor physical impact. Indications for diagnosis and treatment can be established by estimating the absolute fracture risk, taking into account bone mineral density, age, gender, and individual risk factors. Exercise, intervention programs to avoid falls, and specific drugs are capable of substantially reducing fracture risk even in the elderly. Secondary osteoporosis primarily requires both bone-altering medications and effective treatment of underlying diseases.

Hypophosphatemic rickets and osteomalacia

The hypophosphatemic conditions that interfere in bone mineralization comprise many hereditary or acquired diseases, all of them sharing the same pathophysiologic mechanism: reduction in the phosphate reabsorption by the renal tubuli. This process leads to chronic hyperphosphaturia and hypophosphatemia, associated with inappropriately normal or low levels of calcitriol, causing osteomalacia or rickets in children and osteomalacia in adults. X-linked hypophosphatemic rickets, autosomal-dominant hypophosphatemic rickets, and tumor-induced osteomalacia are the main syndromes involved in the hypophosphatemic rickets. Although these conditions exhibit different etiologies, there is a common link among them: increased activity of a phosphaturic factor, being the fibroblast growth factor 23 (FGF-23) the most studied one and to which is attributed a central role in the pathophysiology of the hyperphosphaturic disturbances. Activating mutations of FGF-23 and inactivating mutations in the PHEX gene (a gene on the X chromosome that codes for a Zn-metaloendopeptidase proteolytic enzyme which regulates the phosphate) involved in the regulation of FGF-23 have been identified and have been implicated in the pathogenesis of these disturbances. Genetic studies tend to show that the phosphorus homeostasis depends on a complex osteo-renal metabolic axis, whose mechanisms of interaction have been poorly understood so far. This paper reviews the current knowledge status concerning the pathophysiology of phosphate metabolism regulation and the pathophysiologic basis of hypophosphatemic rickets. It also analyzes the clinical picture and the therapeutic aspects of these conditions as well.

Rickets in an adolescent girl

The authors present a case of rickets in an adolescent girl who presented to the emergency department with bone pain. Emergency department staff should be aware that rickets is not just a disease of early childhood.

[Ten fractures in 21 years]

A 78 year old woman had suffered ten spontaneous bone fractures, the first occurring when she was 57 years old. She is now wheel-chair bound. After 21 years, the underlying osteomalacia due to oligosymptomatic celiac disease with malabsorption was diagnosed. The treatment consists of a gluten free diet and substitution of calcium and vitamin D until there is a normalisation of calcium, vitamin D and alkaline phosphatase. Any spontaneous fracture deserves a careful search for metabolic bone disease. An elevation of alkaline phosphatase indicates osteomalacia rather than osteoporosis.

Oncogenic osteomalacia cured by removal of an organized hematoma

OBJECTIVE

To describe a patient with oncogenic osteomalacia whose symptoms were rapidly resolved after surgical removal of an organized hematoma of the hip.

METHODS

A case report is presented, including clinical and laboratory findings. The relevant literature is reviewed, and the current understanding of oncogenic osteomalacia is summarized.

RESULTS

In September 1996, a 44-year-old black woman presented with a 2-year history of bone pain, progressive muscle weakness, depression, osteomalacia, and hypophosphatemia. Her condition did not improve with use of calcitriol and phosphate replacement. During the previous year, her serum phosphorus levels were low, ranging from 1.0 to 2.2 mg/dL, and the levels of serum 1,25-dihydroxyvitamin D [1,25-(OH)2D] were very low, ranging from <5 to 19.4 pg/mL (normal, 15 to 60). The serum 25-hydroxyvitamin D levels were low, ranging from 8 to 14 ng/mL (normal, 9 to 52). The higher values were noted after she had received large doses of phosphate, 1,25-(OH)2D, and vitamin D. During the previous year, her serum alkaline phosphatase levels were high, ranging from 253 to 314 U/L; serum calcium and parathyroid hormone levels were normal. The abnormalities on physical examination were obesity and a 10- by 10-cm firm, poorly demarcated mass superior to the left greater trochanter. A computed tomographic scan of this region showed a water-density fluid collection in the left buttock measuring 7.8 by 7.8 cm, consistent with a chronic hematoma. The mass was resected, and histopathologic examination revealed features of an organized hematoma with areas of myxoid changes and cartilaginous metaplasia. Postoperatively, the patient's strength improved, and the levels of serum phosphorus and 1,25-(OH)2D became supranormal.

CONCLUSION

The symptoms and laboratory abnormalities of this patient with oncogenic osteomalacia promptly resolved after resection of an organized hematoma of the left hip.

Tumor-induced osteomalacia

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic form of renal phosphate wasting that results in severe hypophosphatemia, a defect in vitamin D metabolism, and osteomalacia. This debilitating disorder is illustrated by the clinical presentation of a 55-year-old woman with progressive fatigue, weakness, and muscle and bone pain with fractures. After a protracted clinical course and extensive laboratory evaluation, tumor-induced osteomalacia was identified as the basis of her clinical presentation. In this article, the distinctive clinical characteristics of this syndrome, the advances in diagnosis of TIO, and new insights into the pathophysiology of this disorder are discussed.

Severe hypophosphatemic osteomalacia in hormone-refractory prostate cancer metastatic to the skeleton: natural history and pitfalls in management

We report the case of a severe symptomatic hypophosphatemic osteomalacia in a 66-year-old patient with hormone-refractory prostate cancer metastatic to the skeleton. A follow-up of 2 years from diagnosis to development of hormone refractoriness and death allowed us to study the natural history of this uncommon disturbance of mineral homeostasis in this common malignancy. Relevant to the difficult management of the late stages of prostate cancer is the failure of hypophosphatemia to respond to conventional therapeutic approaches and the favorable outcome of antitumor therapy suggesting that this group of patients, although having a poor prognosis, could still benefit from aggressive second line therapy. In this malignancy in which metastases have a predilection for bone, failure to recognize osteomalacia can only result in significantly increasing the burden of skeletal complications.

Bad to the bone: the effects of liver diseases on bone

Metabolic bone disease (MBD) is a relevant complication of long-standing liver disease. It has been described in association with most types of chronic liver disease both cholestatic and non-cholestatic. It can significantly affect morbidity, and quality of life of these patients. Fractures are also associated with an excess mortality. Recently, the issue of MBD in liver disease has been considered to be such an hot topic to be the subject of 2 recent review/guideline articles produced by the British Society of Gastroenterology and the American Gastroenterological Association. Aim of this paper is to summarize some practical issues regarding this topic and to provide a rapid overview of the main pathophysiological and pharmacological aspects.

Musculoskeletal manifestations of osteomalacia and rickets

Osteomalacia (OM) is still an important metabolic bone disease with increased prevalence in certain regions of the world as well as in the urban population of elderly confined. The disease presents with a wide variety of clinical, biochemical and radiographic manifestations mimicking other musculoskeletal disorders, including 'osteoporosis'. In this chapter, we provide the basis for its clinical diagnosis and management. There have been significant recent advances in the understanding of vitamin D deficiency and hypophosphataemic osteomalacia, which can now assist clinicians in the precise diagnosis and treatment of this disease. In this chapter we also review the various underlying aetiologies. The successful management of OM depends on the underlying aetiology.

Disorders of phosphate metabolism--pathomechanisms and management of hypophosphataemic disorders

Hypophosphataemia does not necessarily indicate phosphate (Pi) depletion. In acute emergencies such as septicaemia, alkalosis or re-feeding, hypophosphataemia may result from redistribution of Pi from the extracellular to the intracellular space. Hypophosphataemia from true Pi depletion gives rise to skeletal (osteomalacia) and extraskeletal (myopathy, cardiomyopathy) disorders. It is practically never the result of diminished nutritional intake. The most severe syndromes of Pi depletion result from diminished tubular Pi re-absorption and renal Pi wasting. In the differential diagnosis mainly four conditions have to be considered: (i) tumour-associated osteomalacia, (ii) X-linked hypophosphataemia (XLH), (iii) autosomal dominant hypophosphataemia, and (iv) hypercalcaemic renal phosphate wasting. Recent molecular insight has put fibroblast growth factor (FGF-23) into the centre of pathophysiological considerations because of (i) overproduction (tumour-associated osteomalacia) or (ii) hypothetically, accumulation resulting from mutations causing resistance to processing or degradation (autosomal dominant hypophosphataemia) or (iii) loss-of-function of a protease (PHEX) interfering with FGF-23 breakdown (XLH). In oncogenic osteomalacia the treatment of choice is resection of the tumour. Recently, pharmacological treatment has also become possible, i.e. administration of octreotide. XLH and autosomal dominant hypophosphataemia must be managed by oral administration of phosphate and calcitriol. In patients with gastrointestinal intolerance to phosphate or with severely symptomatic bone disease, prolonged intravenous administration of Pi is necessary.

Metabolic bone disease: an update

Metabolic bone disease and some of the disorders of the skeleton are associated with alterations in calcium and phosphorus homeostasis. For example, calcium salts are not freely soluble in body fluids and increases in either calcium or phosphate or both can lead to deposition of calcium salts in the soft tissues. In addition, because the crystalline material in bone is very tiny, there is a rapid and very active exchange system with the extracellular space so that disorders of calcium or phosphorus are reflected by a change in bone structure and, in fact, contribute to the ease with which fractures occur. Also, in many disorders, bone formation and destruction are equal in activity but opposite in sign; in some conditions such as osteoporosis, destruction exceeds production and lead to weakness of bone structure. Finally, the transfer of calcium across lumens such as the gut, kidney, or bone requires a system, which consists of parathyroid hormone and 1,25-dihydroxyvitamin D and a low phosphate level.

[Renal osteodystrophy (3); its treatment in dialysis patients]

The prevalence and the clinical gravity of the various histopathological varieties of renal osteodystrophy in dialysis patients depends on the severity of both the aluminium intoxication and that of hyperparathyroidism. The prevalence of bone pains, fractures and hypercalcemias are the highest in adynamic bone diseases (ABD) with severe aluminium intoxication, then in osteitis fibrosa and mixed osteopathy, in the ABD with moderate aluminium intoxication and rare in the mild lesion in spite of similar moderate aluminium intoxication. In the absence of aluminium intoxication, hypercalcemia and hyperphosphatemia prevalence is higher only when intact PTH is more that 4 times the upper limit of normal. When PTH is between 1 and 2 folds the ULN this prevalence is null and bone mineral density is the highest. 2. The low turnover aluminic bone diseases (osteomalacic or adynamic) will be cured by long term deferoxamine treatment. The hazards of such treatment justify the performance of a bone biopsy to ensure the diagnosis. Their prevention relies on adequate treatment of tapwater and definitive exclusion of long term administration of aluminum phosphate binders. 3. Non aluminic osteomalacia will be treated according to the same guidelines given for the uremic patients before dialysis. 4. Non aluminic adynamic bone disease will be cured by means aiming at stimulating PTH secretion as discontinuing 1 alpha hydroxylated vitamin D derivatives, and, if there is no hyperphosphatemia by discontinuation of calcium supplement. In case of hyperphosphatemia in dialysis patients CaCO3 doses have to be nevertheless increased after the dialysate calcium concentration (DCa) has been decreased in order to induce a negative perdialytic calcium balance for PTH secretion stimulation. In the near future substitution of CaCO3 by non calcemic non aluminic phosphate binders will suffice. 5. Osteitis fibrosa due to hyperparathyroidism will be treated first by securing an optimal vitamin D repletion (bringing plasma 25OH vitamin D around 30 and 60 ng/ml or 75-150 nmol/l) and by correcting hypocalcemia and hyperphosphatemia by CaCO3 at high doses (3-12 g/day) taken with the meals. In case of hypercalcemia dialysate calcium concentration will be decreased to correct it or, in a near future, CaCO3 will be decreased to 3 g/day and hyperphosphatemia will be controlled by non calcemic, non aluminic phosphate binders. When hyperphosphatemia is controlled whereas plasma calcium is normal or low, 1 alpha hydroxylated vitamin D derivatives can be administered. 6. Instrumental parathyroidectomy should be considered when plasma levels of intact PTH remain above 7 folds the upper limit of normal whereas hyperphosphatemia persists and hypercalcemia occurs in order to prevent thining of the corticals and subsequent fracture risk. In case of previous exposition to aluminum, a deferoxamine test and/or a bone biopsy will be performed to decide a long term DFO treatment before the parathyroidectomy in order to prevent the transformation of a mixed osteopathy into an aluminic adynamic bone disease. 7. The difficulty of hyperparathyroidism control in dialysis patients is due to poor compliance to phosphate binders and to irreversible parathyroid hyperplasia with occured before the dialysis stage. This stress the primary importance if its early prevention without iatrogenia by first CaCO3 and vitamin D repletion, as soon as the creatinine clearance decreases below 60 ml/min/1.73 m2.