Endocrine Abstracts

JOINT1109

A 17-year-old male patient presented to our hospital with complaints of confusion and seizures. His medical history revealed that three years ago, he suffered a head injury resulting in a brain hemorrhage. He has been taking carbamazepine due to epilepsy. A physical examination showed that the patient’s height was 146,5 cm (-4,7 SDS), and his weight was 48 kg (-3.02 SDS). His blood pressure and pulse rate at admission were 110/80 mmHg and 71 beats/min, respectively. There were no remarkable findings on chest and abdominal examinations. The findings of the neurological examination were unremarkable, except for muscle weakness. In the family history, the parents were consanguineous and one of his sisters was healthy. Initial laboratory testing was as follows: serum sodium 118 mEq/l, potassium 5.3 mEq/l serum osmolality 240 mOsm/kg, uric acid 1.5 mg/dl, urine osmolality 132 mOsm/kg and urine sodium 24 mEq/l. Other laboratory values of the patient are given in Table 1. The findings of an inappropriately concentrated urine (>100 mOsm/kg), low serum osmolality (<280 mOsm/kg) and serum sodium (<135 mEq/l) were compatible with syndrome of inappropriate antidiuretic hormone secretion (SIADH). After fluid restriction to 1000 ml/m²/day, serum sodium concentration increased up to 141 mEq/l. Since carbamazepine is known to cause SIADH, his treatment was switched to levetiracetam. Further studies were conducted to determine the cause of SIADH. Chest X-ray and magnetic resonance imaging of the brain were normal. When daily fluid intake became unrestricted, hyponatremia recurred. After exclusion of usual causes of SIADH, a nephrogenic origin of inappropriate antidiuresis was considered and the plasma renin activity (PRA), aldosterone level was checked. In the presence of hyponatremia (116 mEq/l) and high PRA (> 1000 ng/ml/h), the aldosterone level was undetectable (<0.01 ng/dl). Therefore, we switched our clinical diagnosis of SIADH to ASD. To correct hyponatremia, fludrocortisone treatment (0.2 mg/day) was started. The diagnosis of ASD was confirmed by genetic testing, which showed a homozygous mutation in CYP11B2 gene, (c.1360>T; p.(Arg454Cys)).