Hypotonic
hyponatremia by
primary polydipsia can cause severe neurologic
complications due to
cerebral edema. A 10-year-and-4-month-old boy with a psychiatric
history of
intellectual disability and behavioral disorders
who presented with chief complaints of seizure and mental change showed severe hypotonic
hyponatremia with low
urine osmolality (
serum sodium, 101 mmol/L;
serum osmolality, 215 mOsm/kg;
urine osmolality, 108 mOsm/kg). The
patient had been polydipsic for a few months prior, and this had been worse in the previous few days. A
diagnosis of hypotonic
hyponatremia caused by
primary polydipsia was made. The
patient was in a
coma, and developed respiratory arrest and became
brain death shortly after admission, despite the
treatment. The initial
brain magnetic resonance imaging showed severe
brain swelling with tonsillar and uncal herniation, and the
patient was declared as
brain death. It has been reported that
antidiuretic hormone suppression is inadequate in
patients with chronic
polydipsia, and that this inadequate
suppression of
antidiuretic hormone is aggravated in
patients with acute
psychosis. Therefore,
hyponatremia by
primary polydipsia, although it is rare, can cause serious and
life-threatening neurologic
complications.