Severe hypernatraemia due to nephrogenic diabetes insipidus - a life-threatening side effect of chronic lithium therapy.

Renal toxicity of long-term lithium therapy is a common problem. Nephrogenic diabetes insipidus is the most frequently encountered complication, but often remains unrecognised because of the rather benign symptoms. We present a patient with long-term lithium therapy who developed life-threatening hypernatraemia due to insufficient oral fluid intake after elective spinal surgery. Careful daily substitution of up to 25 l of hypotonic fluids led to full recovery within 9 days. Nephrogenic diabetes insipidus should always be considered in lithium-treated patients undergoing elective surgery in order to avoid severe hypernatraemia.