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In conjunction with BMJ Case Reports, DTB will feature occasional drug-related cases that are likely to be of interest to readers. These will include cases that involve recently marketed drugs for which there is limited knowledge of adverse effects and cases that highlight unusual reactions to drugs that have been marketed for several years.
Summary
A 40-year-old Caucasian man developed excessive thirst and polyuria particularly at night over the preceding 6 months. He had been taking lithium for 16 years for the treatment of bipolar affective disorder. Investigations revealed subnormal maximum urinary concentrating ability after 8 hours of water deprivation and only a borderline response of urine osmolality to exogenous desmopressin given by intramuscular injection. A plasma copeptin concentration was elevated at 23 pmol/L. These results were consistent with partial nephrogenic diabetes insipidus. He was encouraged to increase his water intake as dictated by his thirst. In addition, he received amiloride with some improvement in his symptoms. Clinicians should be aware of the risk of nephrogenic diabetes insipidus with long-term lithium use and seek confirmation by a supervised water deprivation test augmented with a baseline plasma copeptin. If increased water intake is insufficient to control symptoms, amiloride may be considered.
Background
Lithium is widely used in the treatment of depression and bipolar disorder. In chronic use, lithium accumulates in the distal tubular cells of the kidneys producing a defect in their concentrating ability. This is manifest as partial or full nephrogenic diabetes insipidus (NDI). The diagnosis is confirmed by elevated levels of circulating arginine vasopressin (AVP). More recently, measurement of plasma copeptin, the C-terminal glycoprotein moiety of the AVP prohormone, has been shown to offer advantages over measuring circulating AVP and can reliably discriminate between central and nephrogenic diabetes insipidus (DI). We report a patient with partial NDI associated with chronic lithium …
Footnotes
Contributors EN reviewed the patient in the clinic and produced the first draft of the manuscript. SH revised the manuscript, prepared it for submission and prepared a revised manuscript in line with the reviewers' comments. NJ contributed to discussion and final draft of the manuscript.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Patient consent for publication Obtained.
Provenance and peer review Not commissioned; externally peer reviewed.