A pediatric hypophosphatemic rickets on MRI, ^99mTc-MDP bone scan and ¹⁸F-FDG PET/CT

We present a case of a 13 years old boy who was hospitalized with a 10 months history of progressive pain and weakness in his lower extremities. The laboratory tests revealed slightly decreased phosphate and 25-hydroxyvitamin D3, high alkaline phosphatase, normal calcium and parathyroid hormone (PTH). Magnetic resonance imaging (MRI) showed multiple patchy lesions indicating bone destruction in the metaphyses and epiphyses of the left knee. Fluorine-18-fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT) revealed a generalized decrease of bone density in axial bones with slightly increased ¹⁸F-FDG metabolism. Whole body technetium-99m methylene diphosphonate (^99mTc-MDP) scintigraphy revealed multiple areas of increased uptake at costochondral junctions of the ribs bilaterally suggesting a rachitic rosary and at the metaphyses of the bones of the limbs. Based on these findings we suggested the diagnosis of hypophosphatemic rickets (HPR). Phosphate and vitamin D substitution resulted in clinical improvement of the symptoms after 3 months.