Challenging case of tumour-induced osteomalacia

Abstract

Tumour-induced osteomalacia (TIO), also known as oncogenic osteomalacia, is an uncommon paraneoplastic syndrome which poses a diagnostic challenge. The hallmark feature is severe acquired hypophosphataemic osteomalacia due to renal phosphate wasting because of increased secretion of fibroblast growth factor 23 (FGF-23). A man in his 30s, presented with a 4-year history of severe muscle aches, bone pain and proximal muscle weakness, was referred for evaluation. His laboratory examination revealed severe hypophosphataemia as a result of urinary phosphate wasting, low 1,25-dihydroxyvitamin D, high alkaline phosphatase and elevated FGF-23. We could localise the tumour to his right femur and the biopsy showed a mesenchymal origin. The treatment with pharmacotherapy and radiofrequency ablation helped in the normalisation of blood chemistry and resulted in significant clinical improvement. Hypophosphataemia, phosphaturia, elevated FGF-23 and low 1,25-dihydroxyvitamin D level with severe musculoskeletal pain and muscle weakness necessitate careful evaluation of TIO.

Keywords: Neuromuscular disease; Neurooncology.

Figure 1

Functional imaging ⁶⁸Gallium-(DOTATATE) positron emission tomography/CT showing sclerotic foci in the greater trochanter of the right femur.

Figure 2

MRI of the pelvis short tau inversion recovery sequence showing lesions measuring 2.9×2.1 cm and 7×5 mm in greater trochanter and inferior to it.

Figure 3

A low-power (20× objective) view of H&E-stained section of a cellular soft tissue tumour comprising of benign bland spindle (T) cells arranged in nests and distorted cords infiltrating into the surrounding lamellated bony fragments (B).

Figure 4

A high-power (40× objective) view of H&E-stained section shows tumour cells (T) comprising of plump to spindle-shaped cells with dense nuclei and abundant eosinophilic cytoplasm. Few areas show focal chondromyxoid matrix (M) along with adjacent areas of haemorrhage (H). There is no increased mitotic activity noted, and no necrosis seen.