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109
Relation of
the inoidence
to that of
other
diseases.
Other epidemic diseases affecting the nervous system have been prevalent
during this century, especially poliomyelitis and cerebro-spinal fever. The case
incidence of the latter, which was very high in the years 1915 to 1917, has fallen
materially since that date, so much so as to raise some doubt as to whether certain
cases which might in the former years have been called cerebro-spinal fever, may not
have latterly been termed encephalitis lethargica.
The outbreak of these diseases has borne a distinct relation in point of time
to that of influenza. Some forms of influenza have given rise to nervous symptoms of
a similar character, though milder in degree and of shorter duration than those noted
in epidemic encephalitis. For example, somnolence and later irritability were
commonly observed in 1924, while double vision occurred occasionally. The
infectivity of encephalitis is apparently of a very low order if attention be paid to
cases only showing nervous symptoms. It is, however, possible that the infection
may be conveyed by those in whom the disease takes some other form, or by the
apparently healthy. Some indeed hold that epidemic encephalitis is only one of
the protean forms of influenza, but this view, though strongly supported and, on the
whole, gainins in favour, has not as vet received anv official acceptance.
Sequelae.
The peculiar complications associated with the disease may arise in the course
of the original illness and persist afterwards, or they may supervene after the acute
attack has passed off. recurring even as long as two years afterwards. The more
serious sequelae may follow an apparently very mild or even an unrecognised attack.
These sequelae depend on the localisation of the secondary changes which follow
the original inflammation, and may be classed under two main headings, motor and
mental.
The motor changes may be stiffness or paralysis of certain muscle groups, respiratory
changes and spasms, tremors or jerky movements of muscles of the limbs,
diaphragm or larynx, halting movements, or the condition known as "Parkinsonism,"
which is practically identical with senile shaking palsy.
The mental symptoms vary with the age of the individual at the date of onset
of the acute illness. In young children, the mental growth may be checked and
any grade of idiocy, imbecility or feebleness of mind may result. Increased irritability
alternating with mental hebetude is usual, while there may be maniacal
outbursts, loss of self-control or a complete change of character, the previously wellbehaved
child taking to lying or theft. Hysterical outbursts are quite common.
The effects of the encephalitis are to increase the irritability and diminish the powers
of self control, the form of the resulting behaviour depending, in the main, on the
previous experience and original mental make-up of the individual. The most
difficult cases are those in which both parents and children have a markedly nervous
disposition and act as mutual irritants one to another.
The extent to which sequelae occur is not definitely known, owing to the number
of mild cases which attract little attention, but out of some 800 cases of those who
survived the initial illness that have come under observation, about half of whom
had not originally been notified, 137 are known to have suffered from some sequelae.
More definite information is available as to the cases affected in the early months
of 1925, though the length of time since the onset is insufficient to permit of a final
conclusion as to their prospects.
An analysis of 222 cases out of 305, which were notified during 1925, showed that
45 later proved not to have suffered from encephalitis but from some other ailment.
Of the 179 genuine cases, 81 died, or 45.3 per cent. The highest mortality
occurred in the age group over 55 years—i.e., of the 21 cases, 17 died, or 81 per cent.
The lowest mortality was in the age group 25-35 years—viz., of the 17 cases, 4 were
fatal—23.5 per cent.
These cannot be regarded as the final figures, however, as death sometimes
ensues one, two, three, four or more years after the onset. Relapses are also not
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