[Two cases of infantile autism with intermittent water intoxication due to compulsive water drinking and episodic release of antidiuretic hormone (SIADH)].

The syndrome of water intoxication, resulting from dilutional hyponatremia and characterized by lethalgy, confusion, seizures, and coma was seen in two autistic boys living in the institution for mentally retarded children. Patient 1, a 19 year-old autistic boy showed loss of attention, inactiveness, sleepiness and delirium and then followed by overbreathing, severe vomiting and finally convulsive seizures several times, or coma, since October 1985. In August 1988, he was admitted with generalized tonic clonic convulsion associated with frequent vomiting EEG showed diffuse spike and wave complex with slow background activity. Laboratory data showed inappropriately high serum ADH level (8.5 pg/ml), low sodium concentration (121 mOsm/m/l), serum osmolality (237 mOsm/l) which was lower than urine osmolality (334 mOsm/l), and remarkable body weight gain (8.5 kg). He was diagnosed as water intoxication due to compulsive water drinking and SIADH. Diminished GH secretion to insulin-induced hypoglycemia and exaggerated prolactin response to LHRH stimulation suggested a hypothalamic lesion. Patient 2, a 17-year-old autistic boy, showed essentially the same symptoms and laboratory data as Patient 1, except that he had no epileptic discharge in EEG, and curious GH response to insulin-induced hypoglycemia. A remarkable daily body weight change suggested excessive water drinking and a possible episodic release of ADH. With mild water restriction, this became smaller. Since Patient 1 had epileptic attacks several times without hyponatremia and his EEG showed epileptic discharges, he was diagnosed as having epilepsy. Patient 2 has been seizure-free until now. Abnormality of hypothalamic or pituitary defects and polydipsia and possibility of water intoxication should always be considered when an autistic patients shows recurrent epileptic attacks or episodic strange behaviors with hyponatremia.