Kinematics of fast wrist movements in manic-depressive illness chronically treated with lithium carbonate

Lithium salts have been shown to impair kinematics of fast voluntary movements during acute intoxication. The aim of the present study was to determine whether lithium carbonate affected the kinematics of fast movements in patients chronically treated and who did not exhibit signs of neurotoxicity. We analysed fast wrist flexion movements in 6 healthy subjects, in 5 patients presenting a manic-depressive illness without treatment, and in 8 patients receiving lithium carbonate for a manic-depressive disease. The mean duration of treatment was 3.9 +/- 4.1 years, the mean daily dose 837 +/- 341 mg and the mean serum level 0.95 +/- 0.15 mEq/l. Although mean movement amplitudes were similar in the 3 groups, the variability of fast movements was increased in patients receiving lithium salts. The ratio of maximum to average velocities (Vm/Vave) was significantly higher in patients treated, and their movements were temporally asymmetrical, with a ratio of acceleration duration divided by deceleration duration being lower than in the 2 other groups. These kinematic abnormalities show that a chronic treatment with lithium salts is associated with an impairment of the cerebellar control of fast single-joint movements.