Management of severe polyuria in idiopathic Fanconi syndrome.

Background: Polyuria is a common problem in patients with tubular diseases, especially for those with CKD and high-output Fanconi syndrome. There are currently no guidelines on how to treat debilitating polyuria, in children or adults, and vasopressin is usually not effective.

Case-diagnosis/treatment: A 13-year-old female with idiopathic Fanconi syndrome and an eGFR of 69 mL/min/1.73 m was severely affected by polyuria of 5 L per day (voiding at least 11 times during the day and up to 8 times at night), impacting her mood (measured by the RCADS-child) and academic performance at school. In the absence of guidelines and with literature discouraging the use of indomethacin in this condition, we attempted indomethacin treatment at a dose of 2 mg/kg divided in two doses with substantial success. Urine output dropped to 2.5L and this was accompanied by a substantial decrease of her sodium wasting from 24.6 to 7.7 mmol/kg/day. Over the course of 18 months, the patient's eGFR dropped temporarily to 60 mL/min/1.73 m and was 68 mL/min/1.73 m at last follow-up. However, a sodium-23 (Na) MRI of her thigh revealed ongoing moderate sodium decrease in her skin and substantial Na decrease in her muscle when compared to age-matched peers with normal kidney function.

Conclusions: Indomethacin may be a safe and effective treatment option for polyuria in idiopathic Fanconi syndrome.