A case report on hyponatremia in a patient on chronic lithium therapy

INTRODUCTION: Water intoxication is a rare condition characterized by over consumption of water. In the case outlined below, it emerged as a result of psychogenic polydipsia. CASE REPORT INFORMATION: Here we report an elderly male who presented with polydipsia while being on prolonged lithium therapy for more than 10 years for bipolar affective disorder. Further evaluation showed hyponatremia as a result of water intoxication due to the polydipsia and it confirmed the diagnosis of lithium induced polydipsia which responded to change in the drug and behavioral therapy. INTERVENTION/TREATMENT: Proper evaluation of such a patient was done by comparison of serum and urine osmolality before confirming the diagnosis. The hyponatremia was resolved with water intake restriction. Discontinuation of lithium and start of valproate in such a patient was done. And as the manic phase of the patient subsided the symptoms of polydipsia also decreased. RESULT: His manic symptoms and, as his symptoms improved, the water restriction was more manageable, and the serum sodium levels also increased, after ensuring water intake less than 1.5L per day, following which his serum osmolality and urine osmolality now were in the normal range. DISCUSSION: Polyuria may occur more frequently with twice daily dosing. Lithium can cause a reduction in urinary concentrating capacity: Nephrogenic diabetes insipidus. Hence the occurrence of thirst and polyuria. This effect is usually reversible in the short to medium term but renal effects may be irreversible after long term treatment: >1.5 years. Psychogenic polydipsia is a disorder that can lead to significant morbidity and mortality and occurs in 6% to 20% of psychiatric patients CONCLUSION: Given how common psychogenic polydipsia is, we suggest that routine enquiry should be made into excessive water intake, in both inpatient and outpatient settings.