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Prompt diagnosis and treatment of hypothyroidism in the first 2 years of age is critical, as untreated hypothyroidism can lead to lifelong intellectual and motor impairment. We present severe hypothyroidism due to iodine toxicity in two infants with kidney failure undergoing peritoneal dialysis (PD) with two different dialysis systems.
Retrospective chart review of two patients, one each from Starship Children’s Hospital in New Zealand and The Hospital for Sick Children in Canada.
Patient 1 is an 8-week-old male with kidney failure on maintenance PD who was found to be severely hypothyroid (TSH >100 mU/L (ref 0.6–8); free T4 3.6 pmol/L (ref 10–30)) following investigation for lethargy. Newborn bloodspot testing, anti-thyroid antibodies and thyroid ultrasound were normal. Iodine toxicity was confirmed with an elevated serum level of 1.87umol/L (ref 0.23-0.63) with the only source being iodine-impregnated PD transfer set caps correlating with an elevated dialysate iodine sample of 10.7 umol/L (ref 0). The dialysis system utilized was Fresenius with pin-locking technology. Patient 2 is an 8-week-old male with kidney failure not on maintenance PD but receiving regular bi-weekly PD catheter flushes. He was found to be severely hypothyroid (TSH >100 mU/L; free T4 <5.2 pmol/L) following investigation for failure to thrive. Like patient 1, other aetiologies were excluded, and iodine toxicity was confirmed with a serum level of 4.21umol/L. The Baxter dialysis system was utilized with the iodine source being the MiniCap™. In both patients, lack of a last dwell resulted in the inability to flush the iodine-contaminated PD fluid from the tubing, resulting in intraperitoneal administration and systemic absorption of iodine. Key points of management were to remove the source of iodine and treat hypothyroidism with supplementation. For patient 1, he was treated solely with thyroxine supplementation until the availability of a non-iodine-impregnated cap which has since been made available by Fresenius. For patient 2, in addition to thyroxine supplementation, dialysis was initiated to remove iodine and due to the lack of an iodine-free MiniCap™, an alternative non-purpose-made cap lined with 70% isopropyl-alcohol (CUROS™) was utilized.
Infants under the age of 1 utilizing PD systems with iodine-impregnated caps should be screened for iodine-induced hypothyroidism. Risk factors for iodine toxicity include lack of a last fill to flush the iodine which has leached into the catheter. Development of effective iodine-free transfer set caps is imperative, but in the interim, early recognition and effective thyroid supplementation are the mainstay of treatment.