Comparison between concentric needle EMG and macro EMG in patients
with a history of polio
vol. 110, no. 11, pp. 1900-1908, Nov. 1999.
Copyright © 1999 Elsevier Science
Acute poliomyelitis causes degeneration of anterior horn cells, followed
by denervation. Reinnervation and muscle fibre hypertrophy are mechanisms
that compensate this loss of neurones. Concentric needle EMG (CNEMG) and
macro EMG are two methods to assess the magnitude of initial involvement
and the compensatory reinnervation. The aim of this study is to explore
the difference between CNEMG and macro EMG describing the status of the
motor unit in patients previously affected by polio.
Macro and concentric needle EMG investigations were performed in 261
muscles in 121 patients with a remote history of polio.
CNEMG was abnormal in 211 muscles, macro EMG was abnormal in 246 muscles.
The macro amplitude was 3-4 times `more abnormal' than CNEMG amplitude
relative to the reference values. CNEMG duration was less abnormal and
showed only weak correlation with macro amplitudes. The most likely
explanation for the difference in magnitude of deviation from reference
values for CMEMG and macro EMG, is a more pronounced `phase cancellation'
between single fibre action potentials in CNEMG; This is supported by
simulation studies reported here.
In conclusion macro EMG better reflects the size of the motor unit than
the CNEMG. For detection of concomitant disorders, CNEMG is the method
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