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This is not the age-distribution that might be expected if chorea were primarily
of rheumatic origin, unless it be argued that the nervous sequelae of rheumatism
delayed their appearance for some years after the other signs. It is generally
agreed that in about 80 per cent, of rheumatic cases there is a history beginning
between the ages of four and nine. There are other features of these "out-of-school"
statistics which suggest that the relationship between rheumatism and chorea has
been somewhat exaggerated in the past. For example, there is not an equivalent
increase in the numbers of rheumatism cases. The proportions of out-of-school
cases stated to be suffering from rheumatism during the last four years were 4.09,
4.82, 5.2 and 4.33 per cent, respectively. Then, again, the incidence of heart
disease amongst the cases certified as choreic is low. In one group of 230 chorea
cases 26 only (11 per cent.) were notified as having cardiac disease. The data
may be somewhat incomplete on this point, but all cases with serious heart-lesions
would come under notice through one channel or another. Previous investigators
have published results indicating that widely varying proportions—between fifteen
and seventy per cent—of chorea cases had cardiac disease. The low incidence of
heart disease in the group of choreic children is all the more significant because it
coincided with a steady increase in the numbers of children suffering from heart
disease. In the last four years the percentage of out-of-school cases with heart
disease was 8.67, 8.69, 8.13 and 10.6 respectively. (It is of interest to note that
not a single case was noted in which chorea was stated to be a sequel to scarlet
fever.)
The general features of the statistics support the conclusion suggested by the
clinical examination of several cases, namely that there is an increasing tendency
to certify as chorea conditions of purely neurogenic character. The substantial
increase of the number of girls of thirteen said to be suffering from chorea is another
proof that what hitherto was regarded as simply adolescent instability is now called
chorea. One explanation of this tendency is that during these last few years this
adolescent nervous instability is decidedly more pronounced than it used to be,
with the result that doctors regard the condition as akin to the more serious disease,
viz., chorea. That there is of late an increase of nervous trouble amongst children is
shown by further analysis of the figures. Those stated to be absent owing to nervous
trouble formed the following proportions of all the cases in the years 1920-23,
8.21, 7.8, 8.44, and 10.05 per cent, respectively. The sudden increase last year may
be merely a spurious variation, but before adopting this view it should be borne
in mind that many of the cases of chorea would be more appropriately classified as
nervous diseases ; and that this woifld raise the proportion of nervous disease to
such an extent as to make it extremely improbable that the variation is merely
accidental.
When seeking an explanation of this increase of adolescent narvous instability,
it is natural and so easy just to say: " The war again." It was suggested that the
numbers of mentally defective amongst war-babies would show a decided increase
above the normal rate ; but there is no evidence of this. The effects of war conditions
upon the nervous condition of the children are, however, more substantial,
and the explanation cannot be so lightly discarded as in many other present-day
problems. The mental injuries that a child of eight or younger received during the
air-raids would be expected to add to the mental conflicts and other features of mental
maladjustment of the adolescent. This explanation is well in line with the more
recent psychological results of the study of the adolescent.
Still more obvious is the result of the severe prevalence of influenza in 1918
and 1919 and the trailing outbreaks which have succeeded that prevalence. Investigations
showed that scarcely a child in school failed to suffer during the prevalence.
The virus of influenza has a predilection for attacking the nervous system, and
many cases labelled chorea are undoubtedly the aftermath of influenza and of
the associated encephalitis lethargica.