Does display sensitivity influence motor latency determination?

It is known that display sensitivity can affect onset latency measurement of compound muscle action potentials (CMAPs). We compared two display sensitivities with respect to intrarater and interrater reliability and measured to what degree display sensitivity influences the motor latency. We asked seven raters to mark the onset points of median CMAPs from 24 patients printed with display sensitivities of 5 mV/division and 0.5 mV/division on paper. The onset latencies were measured, and intraclass correlation coefficients (ICCs) were calculated. Most of the raters had excellent intrarater repeatability within a single sensitivity display setting. In contrast, the intrarater reliability using two different sensitivity settings was poor. ICCs calculated for interrater reliability were 0.93 at 0.5 mV/division and 0.91 at 5 mV/division. On average, the latencies measured at 5 mV/division were about 0.3 ms longer. We conclude that reliability of latency measurement is excellent at either sensitivity; however, it is important to use a consistent sensitivity in order to avoid making measuring errors.