Endocrine Abstracts

Lithium is an effective mood disturbance treatment. Endocrine side-effects include hypothyroidism, hypercalcemia and vasopressin resistance. The latter can resolve on cessation of treatment but may be permanent.

Case Report: A 67 year old female was transferred from a psychiatric unit with deteriorating clinical (anorexia, weight loss and decreased conscious level) and biochemical status: sodium 173 mmol/l, potassium 4.6 mmol/l, urea 22.2 mmol/l, creatinine 193 umol/l, calcium 2.77 mmol/l, plasma osmolality 351 mmol/kg and urine osmolality 148 mmol/kg. Treatment with lithium modified-release 400 mg od for 15 years had stopped 2 months earlier. Dehydration with acute kidney injury due to decreased fluid intake was diagnosed. Vigorous fluid resuscitation corrected biochemical abnormalities with return to the psychiatric unit. Four months later a similar episode occurred with the same treatment and outcome. A further episode 3 months later was attributed to dehydration secondary to primary hyperparathyroidism: calcium 2.94 mmol/L and PTH 4.7 pmol/l. Treatment with cinacalcet and IV fluids improved calcium with only a transient improvement in sodium resulting in endocrine referral. The latter diagnosed unrecognised vasopressin resistance leading to the clinical and biochemical abnormalities. This was confirmed with untreated urine volumes of 3.5 L/24h and raised copeptin level of 33 pmol/l coincidental with sodium 167 mmol/l, plasma osmolality 361 mmol/kg and urine osmolality 205 mmol/kg. Treatment with cinacalcet was stopped and consistently normal biochemical levels ensued with urine volumes of approximately 2 L/24h on treatment with acetazolamide 500 mg bd.

Conclusion: (1) patient had mild vasopressin resistance decompensated with decreased oral fluid intake when unwell; (2) relatively mild polyuria secondary to vasopressin resistance can result in severe hypernatremia and (3) clinicians of all specialties need to be aware that nephrogenic diabetes insipidus can occur post lithium treatment.