Physiological characteristics of tremor after chronic lithium therapy.

Twenty-three patients taking lithium carbonate alone in therapeutic dosage for a mean period of 43 months (range 6--108 months) and 23 control subjects matched for age and sex had the frequency and amplitude of postural tremor measured and extrapyramidal symptoms assessed by standard techniques. Patients on lithium had a significantly lower peak frequency of tremor than control subjects (P less than 0.05) and significantly greater extrapyramidal symptoms (P less than 0.01), indicating that tremor appearing after chronic lithium therapy is likely to be an extrapyramidal symptom. Such symptoms are common long-term adverse effects of lithium carbonate.