Most
movement disorders in psychiatric patients are induced by
neuroleptic antipsychotic medications, all of which are
dopamine D2 receptor blocking drugs. These include: acute onset disorders: dystonic reactions,
akathisia and the
neuroleptic malignant syndrome (NMS); non-acute onset
parkinsonism; and the tardive syndromes. However, many other medications, when used at recommended doses, also induce
movement disorders, with
tremor being the most common. With the exception of
serotonin syndrome, they are rarely as severe or disabling as the
neuroleptic extrapyramidal syndromes may be. The
serotonin reuptake inhibiting (SSRI) drugs are associated with the
serotonin syndrome, a life-threatening disorder, but may also cause
tremor and
akathisia. While SSRI's have been thought to occasionally cause a
tardive dyskinesia-like syndrome, this almost never occurs without prior or concurrent
neuroleptic exposure as well. There also are few reliable data to support an association between
antidepressants and
parkinsonism.
Valproic acid has been shown to cause
parkinsonism, and
lithium may as well, in addition to both having the well-known side effect of
tremors.
Myoclonus and
asterixis are usually induced by toxic levels of medications but may appear with therapeutic levels, particularly with
anticonvulsant mood stabilizers, and
clozapine.
Ataxia rarely occurs with non-toxic levels of drug, particularly
anticonvulsants,
benzodiazepines and
lithium.