Chapter 68 - Oncogenic Osteomalacia

Abstract

This chapter focuses on oncogenic osteomalacia (tumor-induced osteomalcia), in which renal phosphate wasting, low serum 1,25 dihydroxyvitamin D levels, and osteomalacia occur in association with a variety of benign or malignant neoplasms, disappearing upon removal or irradiation of the neoplasm. Patients with oncogenic osteomalacia have diffuse bone pain and complain of fatigue. The bone pain can be localized to the lower back, the pelvis, and/or the femurs. Occasionally the patients develop fractures of the fibs, pelvis, femoral neck, or tibia. These fractures may occur with minimal trauma or be pseudofractures, which occur more commonly in patients with osteomalacia. In addition to skeletal pain and fatigue, patients may have a proximal myopathy, making it difficult for them to climb steps or rise from a squatting position. Most tumors that cause oncogenic osteomalacia are of mesenchymal origin and are found in either bone or soft tissue. Patients with these tumors range in age from 17 to 88 years. Tumor locations include the lower limbs, nasopharynx, mandible, ethmoid sinus, skull, cervical spine, upper extremities, and the abdominal wall. Most tumors are skeletal with involvement of long bones; however, occasionally widespread osteolytic lesions are also found. The most important therapy for oncogenic osteomalacia is removal of the offending neoplasm. In cases where the neoplasm can not be resected, therapy with oral phosphate supplementation and 1,25(OH) 2 D 3 ) can improve the serum phosphate and 1,25(OH) 2 D 3 levels.