Reversible renal insufficiency attributable to thyroid hormone withdrawal in a patient with type 2 diabetes mellitus

To present a case of papillary thyroid carcinoma and the need for follow-up surveillance in a patient with type 2 diabetes mellitus who was being treated with metformin.

The clinical and laboratory findings are summarized, and results of whole-body scanning are described. A discussion addresses the importance of monitoring renal function during thyroid hormone withdrawal for scintigraphic imaging with use of radioactive iodine.

A 60-year-old man with type 2 diabetes was diagnosed with metastatic papillary thyroid carcinoma, and renal insufficiency developed during withdrawal from thyroid hormone for surveillance 131 I whole-body scanning. An increase in thyroglobulin attributable to recombinant human thyrotropin stimulation led to detection of persistent cancer, and thyroid hormone withdrawal was begun in preparation for further 131 I treatment. Pretherapy laboratory results revealed a thyrotropin level of 46.1 mIU/mL, a thyroglobulin level of 13.7 ng/mL, and an increased serum creatinine (Cr) concentration from a baseline of 0.9 mg/dL to 1.9 mg/dL while the creatinine clearance (CrCl) was 67 mL/min. Therapy with metformin was immediately discontinued. On the basis of results from 131 I whole-body dosimetry, the patient was treated with 250 mCi of 131 I. Levothyroxine therapy was resumed approximately 72 hours after 131 I therapy, and blood tests 2 weeks thereafter revealed a Cr of 1.1 mg/dL and a CrCl of 105 mL/min. The metformin treatment was then reinitiated without any complications.

Patients with hypothyroidism can have up to a 20 to 30% decrease in glomerular filtration rate, which tends to resolve when euthyroidism is achieved. In patients with diabetes taking metformin who have hypothyroidism for any reason including thyroid hormone withdrawal, serum Cr levels should be monitored until thyroid hormone levels normalize. Metformin therapy should be discontinued in patients with significant renal impairment, defined as either a serum Cr level of 1.5 mg/dL or more in men and 1.4 mg/dL or more in women or a CrCl of less than 60 mL/min.