RTMS and auditory verbal hallucinations in patients with schizophrenia: Should left-handers be treated the same as right-handers?

Abstract

Introduction Repetitive Transcranial Magnetic Stimulation (rTMS) is a promising therapeutic option for schizophrenia patients suffering from treatment-resistant auditory verbal hallucinations. Nevertheless, most rTMS studies exclude left-handed patients. This subpopulation of patients is therefore poorly represented in clinical trials using rTMS whereas they represent nearly 14% of the schizophrenic population. Objectives We will attempt to address two issues in this regard: – should we systematically exclude left-handed patients from rTMS studies? – should the same rTMS treatment method be used for left- and right-handed patients? Methods A literature search was carried out from the MEDLINE database with the following keywords: “repetitive transcranial magnetic stimulation”; “schizophrenia” and “auditory hallucinations”. From the 148 articles found, 8 publications including left-handed patients were selected for the literature review. Most studies highlighted a statistically significant therapeutic effect of rTMS for the treatment of resistant auditory verbal hallucinations. However, none specifically compared the difference in efficacy between left- and right-handed patients. Results Literature data was very limited in this field. Handedness appeared to be an important factor that can influence rTMS treatment because handedness is associated with some cognitive functions such as language. Moreover, auditory verbal hallucinations are strongly associated with cerebral activations in language areas. Thus, the rTMS treatment efficacy can vary between subjects depending on handedness and the stimulated target area. Conclusion Even though handedness (left-handed/right-handed) may be considered as a confounding bias for rTMS studies, left-handed patients should not be systematically excluded from clinical trials. Although few studies have reported opposite effects of rTMS in left- and right-handed patients, further studies are needed to determine whether left-handed psychiatric patients should be treated differently to right-handed ones.