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Lithium-induced nephrogenic diabetes insipidus in older people.

PRESENTATION
We report two patients. The first is a 68-year-old woman who presented with a 2-day history of vomiting. She was hypernatraemic and her elevated serum sodium concentration did not improve initially, despite adequate fluid replacement. She subsequently developed polyuria and polydipsia. The second patient, a 77-year-old woman, presented with delirium and severe hypernatraemia after being treated for a chest infection 1 week earlier. Both patients were on long-term lithium treatment.


INVESTIGATION
In both the cases, a supervised water-deprivation test done after normalization of the blood biochemistry showed partial nephrogenic diabetes insipidus.


OUTCOME
Lithium was discontinued.


CONCLUSION
Older people on lithium-especially those requiring supportive care-are at risk of severe hypernatraemia after an acute illness or if their fluid intake is restricted.