Tumor-induced osteomalacia is an acquired and paraneoplastic disorder caused due to humoral products known as phosphatonins produced by the tumors.
The implicated tumors are generally mesenchymal tumors of long bones, distal extremity, sinuses, nasopharynx, groin, etc.
They are benign, slow growing, and predominantly of phosphaturic mesenchymal tumor of mixed connective tissue (PMTMCT) origin.
The tumor produces PTH related peptide (PTH rP). Unlike PTH, PTH rP affects only phosphate transport and has no effect on calcium metabolism.
PTH antagonists do not block PTH rP and its effects are not mediated by cyclic adenosine monophosphate (AMP).
The phosphaturic hormone implicated in tumor-induced osteomalacia is FGF23.
They can present at any age with a longstanding history of bone pains and muscular weakness. They may present as early as infancy.
They usually go undiagnosed for many years.
Biochemical evaluation reveals results similar to that of XLH.
Complete surgical removal of the underlying tumor provides a definitive cure. Hence, it is important to localize the underlying tumor.
Localization can be done with octreotide scintigraphy, 18F-fluorodeoxyglucose positron emission tomography (FDG-PET), whole-body magnetic resonance imaging (MRI), or whole-body venous sampling of FGF23.
When the tumor remains obscure, phosphate and 1,25(OH)2 D 3 is given in a manner similar to that of X-linked hypophosphatemic rickets.
Complete surgical removal of the underlying tumor provides a definitive cure.