Antipsychotic treatment with quetiapine increases the cortical silent period

Measurement of motor cortex excitability with single and paired pulse transcranial magnetic stimulation has become an established method for in vivo characterization of the effects of central-acting drugs. The comparison of drug-free and medicated patients with schizophrenia suggests an association of neuroleptics intake and prolongation of the cortical silent period (CSP). However all available data come from cross-sectional non-randomized studies. Thus it is not clear whether the observed difference is an effect of medication or reflects differences in disease severity or both.

We aimed to investigate whether the CSP or other parameters of cortical excitability change, when cortical excitability is measured in drug-free patients with acute psychosis before and after 3week intake of the atypical neuroleptic quetiapine.

Different parameters of cortical excitability were studied in 24 drug-free patients with acute psychosis before and after 3weeks of treatment with a mean dose of 352±199mg quetiapine.

We observed a significant prolongation of the cortical silent period (CSP) after three week treatment with quetiapine. Other parameters of cortical excitability such as motor threshold (MT), short intracortical inhibition (SICI) and intracortical facilitation (ICF) remained unaffected. There was a significant improvement in clinical parameters (PANS, GAF) but no significant correlation between clinical improvement and changes in cortical excitability.

These longitudinal data are in line with previous reports from cross-sectional studies. The excitability changes induced by three-week intake of quetiapine in acute psychotic patients confirm the notion that neuroleptic treatment is associated with an increase in CSP.