Age-related changes in motor unit number estimates in adult patients with Charcot-Marie-Tooth type 1A.
BACKGROUND
Charcot-Marie-Tooth disease type 1A (CMT1A) is known as a demyelinating hereditary neuropathy. Secondary axonal dysfunction is the most important determinant of disease severity. In adult patients, clinical progression may be because of further axonal deterioration as was shown with compound muscle action potential (CMAP) amplitude reductions over time. The motor unit number estimation (MUNE) technique may be more accurate to determine the number of axons as it is not disturbed by the effect of reinnervation. The purpose of this study was to investigate the number and size of motor units in relation to age in patients and controls.


METHODS
In a cross-sectional design, we assessed arm and hand strength and performed electrophysiological examinations, including CMAP amplitudes and MUNE of the thenar muscles using high-density surface EMG in 69 adult patients with CMT1A and 55 age-matched healthy controls.


RESULTS
In patients, lower CMAP amplitudes and MUNE values were related to hand weakness. The CMAP amplitude and MUNE value of the thenar muscles were significantly lower in patients than in controls. CMAP amplitudes declined with age in controls, but not in patients. MUNE values declined with age in both patients and controls.


CONCLUSIONS
The age-dependent decrease in the number of motor units was not significantly different between patients with CMT1A and controls, indicating that loss of motor units in adult patients is limited.
van Dijk
J P
JP
Department of Clinical Neurophysiology, Radboud University Nijmegen Medical Centre, PO Box 9101, 6500 HB Nijmegen, The Netherlands. h.vandijk@neuro.umcn.nl
Verhamme
C
C
van Schaik
I N
IN
Schelhaas
H J
HJ
Mans
E
E
Bour
L J
LJ
Stegeman
D F
DF
Zwarts
M J
MJ
D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D001369:Axons / Q000502:physiology; D002607:Charcot-Marie-Tooth Disease / Q000503:physiopathology*; D003430:Cross-Sectional Studies; D004576:Electromyography; D004594:Electrophysiology; D005260:Female; D018737:Hand Strength / Q000502:physiology; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D008297:Male; D008875:Middle Aged; D009046:Motor Neurons / Q000502:physiology*; D015999:Multivariate Analysis; D053580:Muscle Strength; D018908:Muscle Weakness / Q000503:physiopathology; D018482:Muscle, Skeletal / Q000503:physiopathology*; D009410:Nerve Degeneration / Q000503:physiopathology*