A case of minimal change nephrotic syndrome with hypothyroidism deterioration.

A 73-year-old woman with Graves' disease underwent total thyroidectomy and was being treated with levothyroxine. She developed edema in the lower region of both legs 1 month before hospitalization. She had a high concentration of urine protein and was hospitalized for further assessment. A urine protein concentration of 4.4 g/day was observed, and she was diagnosed with minimal change nephrotic syndrome (MCNS) after kidney biopsy. The patient's thyroid function had declined, as indicated by a thyroid-stimulating hormone (TSH) level of 139.0 μIU/mL and a free thyroxine (fT4) level of 0.66 ng/dL. She was prescribed 40 mg/day of prednisolone (PSL) and achieved remission. fT4 level normalized on the 36th hospital day. She was in remission subsequently. However, MCNS recurred when PSL was tapered to 10 mg/day. When she was rehospitalized, thyroid function decline was noted once more, with a TSH level of 29.8 μIU/mL and an fT4 level of 0.74 ng/dL. Her oral PSL dose was increased to 30 mg/day, but she did not achieve remission. However, she achieved remission after steroid pulse therapy. After remission, the thyroid function normalized. During the course of her treatment, the levothyroxine dose was maintained at 87.5 μg/day. Therefore, we predicted that the loss of thyroid hormone in urine due to nephrotic syndrome may have led to the aggravation of hypothyroidism. We have reported this case because of its rarity.