larger view)(Note: this page needs updating! Lots of new research has been done recently)
Medical journals continue to publish case reports of this unusal disease, also known as tumor-induced osteomalacia. It is one of the most interesting paraneoplastic syndromes.
Patients present with muscle weakness, bone pain, or fractures. Children will have rickets (bowing at the knees). Xrays disclose osteopenia, Looser's zones or wide epiphyseal plates. Bone scans may show multiple lesions, and increased activity at the ends of the ribs resembles the "rachetic rosary" seen with vitamin D deficiency.
larger view)
Lab values typically include very low phosphate and 1,25-dihydroxyvitamin D, but normal 25-hydroxyvitamin D levels. There is renal phosphate loss, but renal function is otherwise normal. Amino-aciduria, renal tubular acidosis, or glucosuria indicate Fanconi's syndrome, which may resemble oncogenic osteomalacia. Calcium may be normal or slightly low. Parathyroid hormone is increased in some cases. Alkaline phosphate is elevated. Other routine biochemical tests are unremarkable.
Bone biopsies demonstrate osteomalacia.
These photomicrographs demonstrate serious osteomalacia. When measured, 40% of the bone volume was unmineralized osteoid. The osteoid is orange and the mineralized bone is green. The second view, at higher magnification and under polarized light, shows the lamellar nature of the osteoid.
It has been clear for a long time that a humoral substance caused the osteomalacia, because the bone disease resolves when the tumors are resected. Identification of the factor, however, has been very difficult, because the tumors did not grow well in culture or in animals. Recently researchers have been more successful, and the factor appears to be a phosphaturic peptide, "phosphatonin" which acts at the level of the proximal renal tubule, inhibiting sodium-dependent phosphate transport. FGF-23 (one of the fibroblastic growth factors) is elevated in oncogenic osteomalacia, and it increases in normal persons when given a phosphate load, so this is probably the same as phosphatonin. (reported at the 2002 ASBMR meetings) This may be related to the abnormalities seen in patients with x-linked hypophosphatemic rickets, who have a mutation in the PEX gene. The PEX gene-product inhibits phosphatonin, so a defective PEX gene-product will fail to inhibit phosphatonin, resulting in phosphate wasting. The phosphaturia in both cases in associated with inhibition of 1-alpha-hydroxylase, so 1,25-dihydroxy-vitamin D is low. In oncogenic osteomalacia it is very low, and in x-linked hypophosphatemic rickets it is lower than it should be for the level of phosphate.
Chalew, S. A.(1996). Hypophosphatemia induced in mice by transplantation of a tumor-derived cell line from a patient with oncogenic rickets. J Pediatr Endocrinol Metab 9(6): 593-7.
Drezner, M. (1997). Clinical Disorders of Phosphate Homeostasis. Vitamin D. D. Feldman, F. H. Glorieux and J. W. Pike. San Diego, Academic Press: 733-755.
Econs, M. J.(1994). Tumor-induced osteomalacia--unveiling a new hormone. N Engl J Med 330(23): 1679-81.
Gonzalez-Compta, X.(1998). Oncogenic osteomalacia: case report and review of head and neck associated tumours. J Laryngol Otol 112(4): 389-92.
Nelson, A. E.(1997). Oncogenic osteomalacia: is there a new phosphate regulating hormone? Clin Endocrinol (Oxf) 47(6): 635-42.
Reese, D. M.(1997). Oncogenic osteomalacia associated with prostate cancer. J Urol 158(3 Pt 1): 887.
Rowe, P. S.(1996). Candidate 56 and 58 kDa protein(s) responsible for mediating the renal defects in oncogenic hypophosphatemic osteomalacia. Bone 18(2): 159-69.
Rowe, P. S.(1998). The role of the PHEX gene (PEX) in families with X-linked hypophosphataemic rickets [In Process Citation]. Curr Opin Nephrol Hypertens 7(4): 367-76.
Schapira, D.(1995). Tumor-induced osteomalacia. Semin Arthritis Rheum 25(1): 35-46.
Wilkins, G. E.(1995). Oncogenic osteomalacia: evidence for a humoral phosphaturic factor. J Clin Endocrinol Metab 80(5): 1628-34.
