Background. Oncogenic osteomalacia (OO), also known as tumor-induced osteomalacia (TIO), is a rare paraneoplastic syndrome caused by mesechymal tumors secreting fibroblast growth factor 23 (FGF23). Common in middle age, these tumors are often disclosed by progressive generalized bone pain and muscle weakness, along with an altered biochemical profile. Despite its characteristic presentation, the disease is often underrecognized with delayed onset of surgical or pharmacological intervention that can have serious repercussions on the patients' health and quality of life. Case presentation. We describe the case of a 65-year-old Caucasian man presenting TIO with intracranial and spinal localizations and Fanconi-like aminoaciduria. The condition was misdiagnosed and mistreated for three years, leading to loss of self-sufficiency and depression. Following proper identification, the spinal mass was excised with complete remission of the functional symptoms. As it was not possible to remove the intracranial lesion, the patient was treated conservatively with calcitriol and phosphorous supplements that granted good metabolic control up to the time of a recent follow-up visit (at 5 years). Conclusions. The finding of an altered amino acid profile, not usually reported in these cases, should prompt clinicians to a wider usage of these molecules as suitable candidates for metabolic diseases. In addition to providing central information, they are easy to obtain and inexpensive to analyze. Such determination could help to speed up the diagnostic process, as a long-lasting history of misdiagnosis and mistreatments can lead primarily to clinical worsening, but also to the use of expensive, useless medications with side effects that contribute to poor patient health.
Keywords: FGF23; amino acid profile; muscle weakness; oncogenic osteomalacia; tumor-induced osteomalacia.