Informing dose-finding studies of repetitive transcranial magnetic stimulation to enhance motor function: a qualitative systematic review.

OBJECTIVE Repetitive transcranial magnetic stimulation (rTMS) of the lesioned hemisphere might enhance motor recovery after stroke, but the appropriate dose (parameters of rTMS) remains uncertain. The present review collates evidence of the effect of rTMS on corticospinal pathway excitability and motor function in healthy adults and in people after stroke. METHODS The authors searched MEDLINE and EMBASE (1996 to April 2007), their own collection of peer-reviewed articles, and the reference lists of included studies. They included healthy adults or people with stroke who received rTMS to the primary motor cortex to facilitate or inhibit contralateral corticospinal excitability or movement control. FINDINGS Of the 625 references identified, 37 studies were included with 455 healthy adults (34 studies) and 69 people with stroke (3 studies). For healthy adults, the effects of rTMS on corticospinal pathway excitability varied within each frequency, for example, 1 Hz rTMS was found to facilitate, inhibit, and have no effect on amplitude of motor-evoked potentials (MEPs). After stroke there was a trend for recovery of MEPs (ie, presence of MEPs) after 10 daily sessions of 3 Hz rTMS (one study). Motor function in healthy adults might be adversely affected by 1 Hz rTMS (two studies), whereas combined frequency rTMS was found to have no effect (one study). INTERPRETATION There is as yet insufficient published evidence to guide the dose of rTMS to the lesioned hemisphere after stroke to improve recovery of a paretic limb. Moreover, it is apparent that there is variability in response to rTMS in healthy adults. Dose-finding studies in groups of well-characterized stroke patients are needed.