Lithium neurotoxicity: the development of irreversible neurological impairment despite standard monitoring of serum lithium levels.

We report the case of a 44 year old man who presented with a two-month history of dysarthria, ataxia and leg weakness whilst on maintenance lithium for bipolar disorder. Examination revealed significant cerebellar and pyramidal dysfunction. Serum lithium was 1.5 mmol/l, a moderate elevation above his usual stable levels of 0.4-0.8 mmol/l. The patient's past history included hypertension and chronic renal impairment and the development of neurological symptoms coincided with the recent onset of heart failure. On cessation of lithium he partially recovered, the main residuum being persistent cerebellar ataxia. The case is an example of lithium neurotoxicity developing insidiously in the absence of an overt acute phase syndrome, and highlights the need for keen observation of the patient in the hope of preventing permanent deficits.