Tardive Dyskinesia and Thioridazine-Reply

In Reply.—  Tardive dyskinesia is a disorder that is of growing concern to psychiatrists. Although its cause is still unknown, there are a number of leads that are promising. The most widely held current hypothesis is that neuroleptic-induced parkinsonism and TD are consequences of striatal dopamine receptor blockade, in the first instance, and subsequent up regulation, or denervation supersensitivity, in the second.¹⁵ Receptor-binding studies have demonstrated an increase in the number of receptors without changes in receptor affinity for labeled neuroleptics.⁶ While it is presently impossible to measure dopamine receptor blockade in vivo in humans, there is compelling neurologic evidence that such blockade causes disorders of movement.Sandoz is not unique in suggesting a possible relationship between extrapyramidal stimulation (EPS) and TD.^5,7 In addition, the APA Task Force on Tardive Dyskinesia has also recognized this possible relationship.⁸ Furthermore, an ongoing, prospective study has shown that a history