インスリン療法中の糖尿病にみられたSIADHの一例

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A male diabetic patient aged 53 years with the syndrome of inappropriate secretion of antidiuretic hormone (SIADH) is described. The patient had a seven-year history of diabetes mellitus, which was regulated with dialy injections of NPH insulin, 14 units, for six years. He was well until general fatigue and emaciation developed and he entered to our hospital. On admission, he complained of general fatigue. His height was 163 cm and his weight was 37 kg. The 100 gram oral glucose tolerance test indicated a diabetic pattern (blood sugar; 0'; 205 mg/dl, 30'; 345 mg/dl, 60'; 410 mg/dl, 120'; 485 mg/dl). The funduscopic findings showed diabetic retinopathy (Scott II°). The direct and indirect light reflexes were slow in both eyes. The patellar and Achilles' tendon reflexes were weakened in both legs. The motor nerve conduction velocity of the right median nerve was 36 m/sec (normal range; 47-66 m/sec). These data indicated the presence of diabetic neuropathy. The biochemical findings disclosed hyponatremia (110 mEq/l), hypochloremia (82 mEq/l), normokalemia (4.0 mEq/l), low serum osmolality (222 mOsm/l) and high urine osmolality (504 mOsm/l). The creatinine clearance was 80.3 ml/min and the P.S.P. test (15') was 25.5%. A high plasma antidiuretic hormone (ADH) level of 9.8 pg/ml was detected, in spite of low serum osmolality (250 mOsm/l). There was no relation between the serum osmolality and plasma ADH levels. In the water loading test (30 ml/kg), urine volume for 4 hours was only 19% of the loaded water (normal range; more than 80%), the free water clearance failed to rise and plasma ADH was not suppressed. In the water-ethanol loading test (water; 30 ml/kg, ethanol; 0.45 ml/kg), the urine volume for 4 hours was 64% of the loaded water, the free water clearance rose to +2.04 ml/min and plasma ADH fell to 2.5 pg/ ml from 8.4 pg/ml. A low plasma renin activity of 0.1 ng/ml/h and increased circulating plasma volume of 62.9 ml/kg were detected. A chest X-ray and brain CT scan were normal. The patient was diagnosed as having diabetes mellitus with idiopathic SIADH from the above findings. He was treated by the restriction of water intake to 800 ml/day for two months, besides diet-therapy (1200 Cal/day) and a daily injection of 18 units of soluble insulin. As a result, serum sodium rose to 141 mEq/1 and serum osmolality increased to 288 mOsm/l. The graded increase of water intake for three months did not decrease the serum sodium and the osmolality. Both the water loading test (urine volume for 4 hours; 94%, the free water clearance; +4.01 ml/min) and the motor nerve conduction velocity (47 m/sec) had improved, despite the free water intake for six months. The clinical course and the biochemical findings of this patient suggest that the diabetic neuropathy induced SIADH through the impaired afferent nerves from the osmoreceptors.

インスリン療法中の糖尿病にみられたSIADHの一例

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