An extrapyramidal syndrome after lithium therapy.

Two patients developed an extrapyramidal syndrome after therapy with lithium carbonate. Although the clinical features of this syndrome were indistinguishable from those of drug-induced parkinsonism, it was made worse by the anti-parkinsonian drug, orphenadrine. These findings were reproduced later under laboratory conditions when extrapyramidal symptoms and physiological tremor were recorded before and after challenge doses of orphenadrine. This unwanted effect of lithium carbonate may be explained by selective blockade of dopamine receptors.