Identification of a subgroup of tardive dyskinesia patients by pharmacologic probes

Some patients with tardive dyskinesia fit the cholinergic-dopaminergic imbalance theory, but some do not. In an attempt to study his heterogeneity further, the authors measured the responses of 10 patients with tardive dyskinesia to intravenous challenge doses of drugs that facilitate or inhibit acetylcholine transmission (physostigmine or benztropine, respectively). They then measured the response of these patients to an open outpatient deanol trial. They found that the responses of half of the patients followed the classic theory, 2 responded paradoxically, and 3 responsed inconsistently. They suggest that there is a subgroup of tardive dyskinesia patients who fit the theory but that more research is needed to identify the subgroups who do not.