Abstract
1. A study of the strength -duration curves in
Poliomyelitis is of value in making a prognosis
and therefore in directing treatment.
2. Striking changes in the strength-duration curve
accompanying denervation and recovery of voluntary
power, but bear no regular temporal relationship
to clinical recovery.
3. These changes are superficially similar to those
described during degeneration and recovery in
peripheral nerve injuries. In a muscle that
will recover, fluctuations occur in rheobase,
chronaxie, threshold at 0.5 M/S, L assalle' s index,
and number of effective stimuli, but these changes
are superimposed as a relatively normal baseline,
and between the peaks, the values return to normal.
In a denervated muscle, similar fluctuations occur,
but are superimposed as an essentially abnormal
baseline so that the values never fall quite to
normal.
4. It is possible to make a prognosis on the results of
the electrical reactions much earlier than can be
done by clinical means. The optimum time for making
such a prognosis is probably about the 4th week
after the onset of the disease.
5. A good prognosis at the 4th week is based on a
curve with the following characteristics:-
Five or more effective stimuli.
Relatively high rheobase (40).
Relatively low threshold for currents
of short (0.5 M/S) duration (60).
Relatively low chronaxie (0.05).
Relatively low Lassalle's index (1000).
A bad prognosis is based on a curve with the opposite
characteristics.
6. The index:- 1 = C (t - r) + t.
where C = chronaxie
t = threshold at 0.5 M/S duration
r = rheobase
is of value in distinguishing the curves with intermediate
characteristics at the 4th week. This index gives a value of:-
50 and under with normal curves.
150 and under with curves with a good prognosis.
150 and over with curves with a bad prognosis.
7. All these characteristics must be considered together
in making a prognosis because other factors besides
innervation are capable of altering the strength-duration curve (± 10 volts) and the curve of impending
recovery is very like that of denervated muscle.
8. These principles of prognosis may equally well be
applied to partially paralysed as well as completely
paralysed muscles.
Excessive exercise may have a deleterious effect on
partially paralysed muscle.
10. Galvanism probably has no part to play in the
treatment of Poliomyelitis.
11. There is no evidence that mental alienation as
described by Miss Kenny occurs in the disease.
12. This investigation suggests that the following
lines of further work might yield interesting
results : -
a) Strength-duration curves in Poliomyelitis
from the very earliest days.
b) Strength- duration curves as a large number
of muscles at the 4th week after the onset
of the paralysis to determine the reliability
of the suggested index in making a
prognosis.
c) Strength-duration curves of partially paralysed
muscles to determine the value of the
curves in prognosis and the effect of exercises and rest on the recovery in these
muscles.
d) The cause of unusual discomfort which occurs
in a certain number of cases subjected to
this form of examination.
