Effects of chronic lithium treatment on the peripheral nervous system

Background Although lithium carbonate is widely used in the treatment of mo od disorders, symptoms suggesting toxic effects on the peripheral nervous s ystem may emerge even in subjects whose serum lithium levels remain within the recommended therapeutic range. Method: Electroneuronographic (ENG) parameters (motor nerve conduction velo city of peroneal and median nerves, sensory nerve conduction velocity of su ral and median nerves, amplitude of motor potential of peroneal and median nerves, and amplitude of sensory action potential of the median nerve at th e wrist and the sural nerve) were investigated in 2 groups (N = 34) of pati ents suffering from bipolar affective disorder (DSM-III-R, DSM-IV) undergoi ng maintenance treatment with lithium carbonate for at least 1 year (mean = 2.06 years) in monotherapy. For 12 patients, ENG results were compared wit h 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 treate d 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 a nd median nerves, amplitude of motor potential of peroneal and median nerve s, and amplitude of sensory action potential of the median nerve at the wri st and the sural nerve. The comparison with the assessment made prior to li thium treatment also showed significant changes; after a period of treatmen t with lithium varying from 2 to 8 years (mean = 5.2 years), significant re ductions were found on motor and sensory nerve conduction velocity and on a mplitude motor potentials and sensory action potentials. Conclusion: Chronic maintenance treatment with lithium affects the peripher al nerves, even if the impairment rarely is such as to warrant discontinuat ion of treatment. Monitoring of ENG results could be useful for the early d etection of neurotoxicity of lithium.