Endocrine Abstracts

Background: Thyroid hormones are essential for the adequate growth and development of the kidney and also target changes in glomerular and tubular functions and electrolyte and water homeostasis. Hyperthyroidism leads to an increase in glomerular filtration rate (GFR) and renal blood flow with converse effects seen in hypothyroidism. In turn, the kidneys are responsible for the metabolism and elimination of thyroid hormones and thus renal disease can lead to significant changes in thyroid function.

Case: A 7 year old girl of South American ethnicity was referred after blood results showed thyrotoxicosis (fT4 42.1pmol/l, TSH <0.01 mU/l). She presented to her GP with a 3 week history of neck swelling. There was no history of palpitations, sweating, insomnia, loose stool or difficulty in breathing. She was described as doing fairly well in school but being overactive. She had lost 2 kg in weight. She was commenced on carbimazole 10 mg twice daily with stabilisation of her thyroid function with respective dose reduction (ft4 21.0pmol/l, TSH <0.01 mU/l). Due to missed appointments, whilst on treatment she developed profound hypothyroidism (fT4 3.0pmol/l, TSH >100 mU/l) accompanied with significant rise in serum creatinine to 83 umol/l (NR 30–47 umol/l), with normal urea (6.2 mmol/l), sodium (140 mmol/l) and potassium (4.2 mmol/l). Additional renal investigations were normal including renal ultrasound, urine A:CR, P:CR and microscopy. Carbimazole was ceased and both thyroid and renal function showed improvement. Carbimazole was re-started 4 months after as biochemistry showed she was hyperthyroid (fT4 28.4 pmol/l, TSH 0.01 mUL/L) with subsequently stable renal function (55 umol/l; NR 30–47 umol/l).

Discussion: We report a case of Graves’ hyperthyroidism who developed profound hypothyroidism whilst on titrated carbimazole treatment due to missed appointments and subsequent impaired renal function. Given the associations of renal disease and thyroid dysfunction, the patient was investigated for possible underlying renal pathology. Prompt cessation of antithyroid drugs resulted in improvement in both thyroid and renal function. The family were further educated on the importance of close monitoring and signs of thyroid dysfunction. Patients on titrated doses of anti-thyroid medication require close monitoring of thyroid function and renal function.