IMPE Abstracts

Background: Hypophosphatemic rickets can occur due to multitude of conditions. In a child with Ewings sarcoma treated with chemotherapy we need to consider Fanconi syndrome, but FGF23 induced oncogenic hypophosphatemic rickets should also be kept in mind. Proximal tubular dysfunction is a well known cause following treatment with ifosfamide.

Presenting problem: 3 years and 4 months old girl, a diagnosed patient with Ewings sarcoma of left side humerus, presented with recurrent fractures involving right side clavicle and multiple ribs following minor trauma. She was diagnosed with Ewings sarcoma at the age of 1 year and 3 months and given chemotherapy with ifosfamide, etoposide, doxorubicin and vincristine which was followed by surgery and radiotherapy. Clinically she had no polyuria or frothy urine. She was started on vitamin D supplementation for 6 months prior to this presentation. She had mild development regression following her illness which is gradually improving. She had mild widening of wrist and her dentition was normal. Initial investigations revealed normal serum calcium-10mg/dl(8.8-10.8), low phosphate-1mg/dl (4.5-5.5), high ALP-854 U/L while PTH-24.9(15-65) and 25 OH vitamin D(56.03ng/dl)levels were normal. Blood gas revealed metabolic acidosis with pH of 7.25 with HCO3- 10.9. Urine protein creatinine ratio was 184 mg/mmol which was suggestive of non-nephrotic range proteinuria. There was no hypercalciuria. Serum sodium and creatinine were normal and potassium was marginally low (3.4 mmol/l). X-ray knee joint showed evidence of rickets. MRI of the left side humerus revealed no local tumor recurrence.

Clinical management: Hypophosphatemic rickets as a consequence of Fanconi syndrome was diagnosed, with the clinical history and biochemistry in this child. However oncogenic hypophosphatemic rickets with tumor recurrence was excluded by doing FGF23 levels {7.34 Ru/ml (0-150) which was normal. She was started on phosphate supplements with 1 alpha calcidol and potassium citrate following which she showed gradual clinical recovery.

Discussion: Fanconi syndrome is a generalized dysfunction of renal proximal tubule characterized by metabolic acidosis, hypophosphatemia due to phosphaturia, renal glucosuria, aminoaciduria, and tubular proteinuria. Hypophosphatemia can lead to hypophosphatemic rickets as in our patient. Development of renal tubular defects may occur abruptly or can be late even several months or years after exposure following chemotherapy. Finally we should never forget to exclude tumor recurrence, in a child with hypophosphatemic rickets as it is also a rare cause.