Reliability and minimal detectable change of transcranial magnetic stimulation outcomes in healthy adults: A systematic review

Background: Transcranial magnetic stimulation (TMS) is used worldwide for noninvasively testing human motor systems but its psychometric properties remain unclear.

Objective/hypothesis: This work systematically reviewed studies on the reliability of TMS outcome measures of primary motor cortex (M1) excitability in healthy humans, with an emphasis on retrieving minimal detectable changes (MDC).

Methods: The literature search was performed in three databases (Pubmed, CINAHL, Embase) up to June 2016 and additional studies were identified through hand-searching. French and English-written studies had to report the reliability of at least one TMS outcome of M1 in healthy humans. Two independent raters assessed the eligibility of potential studies, and eligible articles were reviewed using a structured data extraction form and two critical appraisal scales.

Results: A total of 34 articles met the selection criteria, which tested the intra- and inter-rater reliability (relative and absolute subtypes) of several TMS outcomes. However, our critical appraisal of studies raised concerns on the applicability and generalization of results because of methodological and statistical pitfalls. Importantly, MDC were generally large and likely affected by various factors, especially time elapsed between sessions and number of stimuli delivered.

Conclusions: This systematic review underlined that the evidence about the reliability of TMS outcomes is scarce and affected by several methodological and statistical problems. Data and knowledge of the review provided however relevant insights on the ability of TMS outcomes to track plastic changes within an individual or within a group, and recommendations were made to level up the quality of future work in the field.