title: Age-dependent decline in motor evoked potential (MEP) amplitude: with a comment on changes in Parkinson's disease.
abstract: Peak-to-peak measurement of the maximum amplitude motor evoked potential (MAXMEP) elicited by 20 consecutive transcranial magnetic stimuli recorded from the contracting thenar and hypothenar muscles measured 9.8 +/- 2.0 mV and 7.25 +/- 2.9 mV respectively (P less than 0.01). The ratio of MAXMEP/CMAP measured 92.6 +/- 25.8% and 54.8 +/- 12.3% respectively (P less than 0.001). Repeat studies showed good individual reproducibility. Amplitudes declined linearly with age (r = -0.836 for thenar MAXMEP P less than 0.001). It is argued that MAXMEP related to age is more meaningful than the MEP/CMAP wave ratio and is proportional to the number of fast conducting cortical motor neurons excited. In 7/18 patients with Parkinson's disease (PD) MAXMEP was increased; in 2 other patients MAXMEP was decreased for their age.
authors.affiliation: Department of Medicine (Neurology), University of British Columbia, Vancouver, Canada.
authors.forename: A
authors.initials: A
authors.lastname: Eisen
authors.forename: S
authors.initials: S
authors.lastname: Siejka
authors.forename: M
authors.initials: M
authors.lastname: Schulzer
authors.forename: D
authors.initials: D
authors.lastname: Calne
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D004576:Electromyography; D005071:Evoked Potentials; D005260:Female; D006801:Humans; D008280:Magnetics; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000502:physiology / Q000503:physiopathology*; D009046:Motor Neurons / Q000502:physiology; D009119:Muscle Contraction; D009132:Muscles / Q000502:physiology / Q000503:physiopathology*; D009431:Neural Conduction; D010300:Parkinson Disease / Q000503:physiopathology*; D012044:Regression Analysis; D015203:Reproducibility of Results; D013933:Thumb