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1978Reches A, Ebstein R, Belmaker RH: The differential effect of lithium on noradrenaline and dopamine sensitive accumulation of cyclic AMP in guinea pig brain. Psychopharmacologia Reches A, Wagner HR, Jackson V, Fahn S: Chronic lithium administration has no effect on haloperidol-induced supersensitivity of pre-and postsynaptic dopamine receptors in rat brain. Brain Res 246:172-177, 1982 Reches A, Wagner HR, Jiang D, Jackson V, Fahn S: The effect of chronic L-dopa administration on supersensitive pre-and postsynaptic dopaminergic receptors in rat brain. We welcome the comments of Drs Reches and Fahn. We agree that the pathophysiology of the "on-off" phenomenon is not known and that the mechanism of action of lithium on dopamine receptors can only be speculated upon at the present time [I, 3, 41. It should be stressed that ours was a clinical study El] designed to evaluate a potentially useful treatment for one of the more disabling complications of parkinsonism. The therapeutic benefits we observed stand despite the suggestion that ". . . basic science studies . . . do not support the use of lithium in the therapy of the 'on-off' phenomenon." The absence of a rationale in no way vitiates an observation but rather demands that further studies be conducted so that these observations may be explained.We find it difficult to compare our results with those of Drs Lieberman and Gopinathan {3]. In contrast to our study, seven of their patients had received pergolide, eight had received lisuride, seven were clinically depressed, self-rating assessments were performed only twice weekly, and serial serum lithium levels were not reported. Nonetheless, three patients were reported to have "increased the number of hours they were on," three patients had decreased "anxietyrelated freezing episodes," and three patients had changes in dyskinesia status.We believe that lithium may be a valuable adjunct in the treatment of the "on-off" phenomenon in some Parkinson's disease patients. Further studies, particularly those aimed at determining whether pretreatment with lithium modifies the development of the "on-off" phenomenon, are encouraged. A 23-year-old male with a normal birth and developmental history who developed psychomotor seizures at age 20 was admitted with a complaint of difficulty in walking over several days. He recently had had his phenytoin dosage adjusted and mistakenly was taking six 100 mg capsules a day. The patient and his mother had noted a "turning in" of the right foot for two days, which interfered. with normal ambulation. Neurological examination revealed normal mental status, horizontal nystagmus, slight bilateral intention tremor, and focal dystonia of the right leg, consisting of sustained plantar flexion and inversion of the foot. The remainder of the examination was normal. The blood level of phenytoin was 60 pg/ml. Electroencephalography showed an interictal left temporal lobe sharp-wave focus. Computed tomographic scan of the head was normal. Phenytoin was withheld, and 24 hours later the dysto...