Effects of chronic lithium treatment on the peripheral nervous system.

Background: Although lithium carbonate is widely used in the treatment of mood disorders, symptoms suggesting toxic effects on the peripheral nervous system may emerge even in subjects whose serum lithium levels remain within the recommended therapeutic range. Method: Electroneuronographic (ENG) parameters (motor nerve conduction velocity of peroneal and median nerves, sensory nerve conduction velocity of sural and median nerves, amplitude of motor potential of peroneal and median nerves, and amplitude of sensory action potential of the median nerve at the wrist and the sural nerve) were investigated in 2 groups (N = 34) of patients suffering from bipolar affective disorder (DSM-III-R, DSM-IV) undergoing maintenance treatment with lithium carbonate for at least 1 year (mean = 2.06 years) in monotherapy. For 12 patients, ENG results were compared with pretreatment values, whereas in the other 22 cases, only data relevant to posttreatment were available. Fifty-four healthy subjects and 20 patients with recurrent major affective disorder (unipolar and bipolar) never treated with lithium made up the comparison groups. Results: Compared with the 2 comparison groups, patients on chronic lithium treatment showed significant reduction of motor nerve conduction velocity of peroneal and median nerves, sensory nerve conduction velocity of sural and median nerves, amplitude of motor potential of peroneal and median nerves, and amplitude of sensory action potential of the median nerve at the wrist and the sural nerve. The comparison with the assessment made prior to lithium treatment also showed significant changes; after a period of treatment with lithium varying from 2 to 8 years (mean = 5.2 years), significant reductions were found on motor and sensory nerve conduction velocity and on amplitude motor potentials and sensory action potentials. Conclusion: Chronic maintenance treatment with lithium affects the peripheral nerves, even if the impairment rarely is such as to warrant discontinuation of treatment. Monitoring of ENG results could be useful for the early detection of neurotoxicity of lithium.