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Full text of "Diseases Of The Nose Throat And Ear"

CHAPTER 63
FACIAL PARALYSIS

Facial paralysis may be due to a lesion of the nerve: (i) within the cranial
cavity, (ii) in its passage through the temporal bone and (iii) after its exit
from the stylomastoid foramen.

Various tests have been devised in order to ascertain the state of the
muscles supplied by the facial nerve. Some give very accurate and valuable
information about the stages of degeneration which the nerve and muscles
may have undergone, and indicate the reparative processes in regeneration.
The faradic and galvanic testsjure of limited value owing to the difficulties
in accurate measurement of the strength of the electrical stimulus in fara-
dism and the duration of the stimulus in galvanism. When the latter test
is employed the reaction of degeneration (RD) takes 10-14 days to appear
following the actual nerve lesion. If there is complete absence of response
to galvanism nerve surgery is useless owing to the advanced atrophic changes
in the muscular tissue,

The ^nfiuctivitv test is a quantitative test of nerve excitability and is
applicable to lesions proximal to the point of stimulation which is at the
stylomastoid foramen. It consists of a comparison of the threshold inten-
sities, on the normal and abnormal sides, required to stimulate the nerve
when the electrode is applied below the ear and an electrical pulse of 1 msec
is passed. The foldings may indicate no degeneration, partial degeneration
or complete degeneration. The test is of value 3-4 days after the onset of
paralysis, and gives a high rate of accuracy in the prognosis of the
palsy.

Another test, interpreted by strength-duration (SD) or intensity curve
(IT), is recorded by means of a special instrument wmcn gives an output
of known strength and duration and is of importance. The technique is
specialized, and the intensity threshold is charted and the state of each
individual muscle must be ascertained (Fig. 177).

Electromyography. This depends upon the presence or absence of contrac-
tion in the muscle fibres when stimulated. With a needle electrode inserted
directly into the muscle, contraction of a functioning muscle will produce
action currents on stimulation, and these may be recorded by amplification
and the sound interpreted by a skilled technician.



and this suggests a poor prognosis. The outlook is more favourable if there
is the occasional appearance of normal motor potentials. Electromyography
records any improvement or recommencement of muscle function before
any clinical sign is apparent. Polyphasic potentials are found a week or
two before clinical evidence of returning movement is detectable, and should
be looked for after 10-12 weeks of complete paralysis as their presence

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