Endocrine Abstracts

Lithium is used in psychiatric practice as maintenance therapy in bipolar disorder. It has a narrow therapeutic index with serious toxic potential. Lithium is associated with multiple endocrine and metabolic disturbances but data regarding the rates of these in individual patients is lacking. In a tertiary referral centre, all patients on lithium therapy from 2000 to 2014 were identified. The aim of this study was to assess the impact of lithium therapy on the development of endocrinopathies.

Results: Five-hundred and eighty patients were identified across the 14-year period. The median number of serum lithium measurements per person was 5 (IQR 11) with a median duration of therapy of 4.2 years (IQR 10). Toxic lithium levels were observed in 27.8% (n=161) of patients during follow up. Impaired renal function was more common in patients with toxic lithium levels compared to those with normal lithium levels (52.8% vs 47.2%, P<0001). Hypernatraemia (sodium >145 mmol/l) was observed in 16.4% of the study population (n=95), and it correlated with impaired renal function (r=+0.5, P<0001). 25.3% (n=24) of patients who had hypernatraemia also developed hyponatraemia during the follow up period. 12/29 patients assessed with hypernatremia had biochemical evidence of nephrogenic diabetes insipidus with a median plasma osmolality 295 mOsm/kg (IQR 17.75) and urine osmolality of 206.5 mOsm/kg (IQR 235).Impaired renal function was observed in 39% (n=226) of the study population. 30.7% (n=178) of patients had a TSH level >4.2 mU/l. Serum calcium was measured in 503 patients with hypercalcaemia observed in 6.4%. 4/16patients (25%) assessed for hypercalcaemia had elevated PTH level but all also had impaired renal function.

Conclusion: Chronic lithium maintenance therapy and impaired renal function were risk factors for toxicity. This study highlights the multiple electrolyte and hormone disturbances observed in patients on lithium. Clinicians should be aware of this in order to monitor, detect and institute early and appropriate management of endocrinopathies.