Case records of the Massachusetts General Hospital. Case 52-1989. A 63-year-old man with osteomalacia and the later development of a right nasal mass

Bone scintigraphic patterns in patients of tumor induced osteomalacia

Tumor induced osteomalacia (TIO) or oncogenic osteomalacia is a rare condition associated with small tumor that secretes one of the phosphaturic hormones, i.e., fibroblast growth factor 23, resulting in abnormal phosphate metabolism. Patients may present with non-specific symptoms leading to delay in the diagnosis. Extensive skeletal involvement is frequently seen due to delay in the diagnosis and treatment. The small sized tumor and unexpected location make the identification of tumor difficult even after diagnosis of osteogenic osteomalacia. The bone scan done for the skeletal involvement may show the presence of metabolic features and the scan findings are a sensitive indicator of metabolic bone disorders. We present the bone scan findings in three patients diagnosed to have TIO.

Cloning of human PEX cDNA. Expression, subcellular localization, and endopeptidase activity

Mutations in the PEX gene are responsible for X-linked hypophosphatemic rickets. To gain insight into the role of PEX in normal physiology we have cloned the human full-length cDNA and studied its tissue expression, subcellular localization, and peptidase activity. We show that the cDNA encodes a 749-amino acid protein structurally related to a family of neutral endopeptidases that include neprilysin as prototype. By Northern blot analysis, the size of the full-length PEX transcript is 6.5 kilobases. PEX expression, as determined by semi-quantitative polymerase chain reaction, is high in bone and in tumor tissue associated with the paraneoplastic syndrome of renal phosphate wasting. PEX is glycosylated in the presence of canine microsomal membranes and partitions exclusively in the detergent phase from Triton X-114 extractions of transiently transfected COS cells. Immunofluorescence studies in A293 cells expressing PEX tagged with a c-myc epitope show a predominant cell-surface location for the protein with its COOH-terminal domain in the extracellular compartment, substantiating the assumption that PEX, like other members of the neutral endopeptidase family, is a type II integral membrane glycoprotein. Cell membranes from cultured COS cells transiently expressing PEX efficiently degrade exogenously added parathyroid hormone-derived peptides, demonstrating for the first time that recombinant PEX can function as an endopeptidase. PEX peptidase activity may provide a convenient target for pharmacological intervention in states of altered phosphate homeostasis and in metabolic bone diseases.

Nasal chondromesenchymal hamartoma: an upper respiratory tract analogue of the chest wall mesenchymal hamartoma

Nasal chondromesenchymal hamartoma is the suggested appellation for a tumefactive process of the nasal passages and contiguous paranasal sinuses in seven children with a detectable mass in the nose. With the exception of one patient who was 7 years of age at diagnosis, the others were 3 months of age or less upon recognition of the mass. Two children were diagnosed in the first 2 weeks of life. Imaging studies showed a complex solid and cystic mass or masses filling the nasal cavity and extending into the ethmoid sinuses in most cases. Erosion of the surrounding bone, including the cribriform plate, resulted in an intracranial component in the four cases. Surgical resection was the treatment of choice despite its technical difficulties that often necessitated a combined intranasal and intracranial approach. Residual disease with continued growth in one case was the clinical outcome in two children, and the remaining five patients have not experienced any further difficulties. The piecemeal fragments of tissue disclosed a collage of histologic features, but the basic morphologic elements were well-demarcated nodules of cartilage with some variation in the cellular density and maturation of the chondrocytes, a myxoid to spindle cell stroma, focal osteoclastlike giant cells in the stroma, and erythrocyte-filled spaces resembling those of the aneurysmal bone cyst. Two of the tumors were less polymorphous or complex in their spectrum of histologic features. These nasal masses have similarities to the so-called chest wall hamartoma or mesenchymal hamartoma of the chest wall in terms of the clinical presentation in infancy and the basic cartilaginous character of both entities. There is a degree of presumption in the designation of these nasal and chest wall tumors as hamartomas because the pathogenesis has not been established for either entity.

Oncogenous osteomalacia and malignancy

An example of oncogenous osteomalacia is described in association with the rate mesenchymal chondroblastoma. The tumour was characterized with a variety of immunohistochemical antibodies which confirmed its mesenchymal origin. Despite several surgical excisions of local recurrence, plasma 1,25-dihydroxyvitamin D3 concentrations (off treatment) indicate continued tumour activity and the continuing need for vitamin D therapy. This case and two others briefly discussed illustrate some of the difficulties in diagnosis and in achieving a cure in cases of oncogenous osteomalacia. Oncogenous osteomalacia in association with any malignant tumour is rare, there being eight previously recorded cases. Details of these cases are briefly reviewed for comparison. Despite undoubted malignancy our patient has survived 30 years from presentation indicating the benefits of aggressive surgical management.

Review and update: oncogenic osteomalacia-rickets

Oncogenic or tumor-induced osteomalacia-rickets is a syndrome characterized by hypophosphatemia, renal phosphate wasting, and decreased serum 1,25-dihydroxyvitamin D3 levels. The tumors secrete a phosphaturic substance that causes total body phosphate depletion, leading to osteomalacia or rickets. Although the tumors are histologically polymorphous, personal review of 16 tumors documented to cause this syndrome revealed four morphologic patterns. The first contained 10 unique-appearing, mixed connective tissue tumors having variably prominent vessels, osteoclastlike giant cells, focal microcystic changes, dystrophic calcification, osseous metaplasia, and/or poorly developed cartilagelike areas. With one exception, all tumors of this group occurred in soft tissue and were benign. The single malignant tumor originated in bone, recurred locally, and metastasized to lung. The remaining tumors occurred in bone and showed benign clinical behavior. They resembled tumors known to occur in bone, that is osteoblastomalike (3 tumors), nonossifying fibromalike (2 tumors), and ossifying fibromalike (1 tumor).