A number of these post influenzal psychoses we kept in hospitals until convalescent, usually after one or more weeks. Of others whom we handed over to the lunatic asylums on account of suicidal tendency or disturbance we heard later that they were soon discharged from these institutions cured. We then regretted that we had not kept back such patients, for the placing of a patient in an insane asylum is not a matter of indifference and should be avoided if possible.
As regards the time of occurrence of influenza psychoses and the different forms of mania, we cannot, of course, examine in detail the copious special literature on this subject.
In very rare cases there may be a prodromal stage, lasting one or more days, of acute afebrile or subfebrile dementia, preceding the influenza attack, it being principally of a melancholic type, with fear, stupor, occasionally also with paranoia, exaltation, increasing to acute mania. Such delirium or dementia is quite analogous to that which occasionally ushers in typhoid fever or pneumonia. (Compare p. 594.) It is quite characteristic of these prodromal psychoses that with the onset of fever and the beginning of the true influenza attack, quietude and consciousness are restored. By the end of the influenza attack the patient has quite recovered, and, furthermore, it is peculiar that this prodromal afebrile delirium and initial psychosis protect from dementia during convalescence rather than predispose to it. No doubt this is due to a purely transitory toxic influence and there can be no question of a peculiar "hereditary or acquired" disposition in these cases. The conditions just described have naturally nothing in common with an initial delirium tremens.
The psychic disturbances occurring during the febrile stage of influenza fall into the class of febrile deliriums, which are nothing but acute transitory toxic mental disturbances. They generally run a uniform course, with more or less total disturbance of consciousness, confusion, with either quiet or excited delusions and hallucinations. They may also simulate many forms of psychoses in a more " limited sense of the term": either the melancholic type, with stupor, fear, total dumbness, refusal of food, and ideas of persecution; or the maniacal type, with fleeting ideas, psychic exaltation, and motor disquietude up to mania; or, finally, the type of hallucinatory confusion. As in all febrile psychoses, there is in influenza also not rarely a marked disproportion between the intensity of delirium and the height of the fever. It is characteristic of the simple, febrile delirium that it ceases with the falling of the body temperature-that is, after the influenza process has ceased.
Psychoses, in the limited sense of the term, occasionally develop, but very rarely, out of the febrile delirium, and are then characterized by the above noted various psychic disturbances continuing for a shorter or longer time beyond the febrile period.
In the majority of cases the commencement of a psychosis follows immediately after the termination of the influenza attack, or in some instances a few days thereafter; less frequently after an interval of one or two weeks. In the latter case it is difficult to conceive the toxic influence still at work. Very likely these conditions are due to after effects, to disturbances in the nutrition of the cerebral cortex induced by the toxins, and progress during convalescence being favored in their course by the other evil after effects of influenza. The general bodily and mental prostration, the insomnia, the anorexia, and the digestive disturbances, sometimes with the addition of excruciating neuralgia, prepare the soil for intense mental depression and hypochondriacal melancholia, which may increase to grave melancholia with an apathy for existence and suicidal tendencies,* with maniacal ideas and delusions of poisoning and persecution, hallucinations, etc.
Undoubtedly the condition of depression, the hypochondriacal melancholia, and the severer forms of melancholia are the most frequent of the post influenzal psychoses. But very nearly all other varieties of acute mental disease are observed after influenza, especially hallucinatory confusion with considerable disturbance of consciousness, with delusions and insane ideas, principally of a depressive, rarely of an exalted, character, with either absence or presence of motor disturbance, which may occasionally also be increased. These are the so called " exhaustion or collapse psychoses " of alienists.
* During the time of the pandemic of 1889-1890 the number of suicides in Paris increased 25 per cent, (quoted from Bossers).
A third, by far rarer, form of post influenzal psychosis is the maniacal disturbance characterized by fleeting ideas and chattering incoherence, with varying but usually exalted moods, great restlessness, which may increase to destructive or maniacal fury. Conditions of this nature are sometimes difficult to differentiate from the excited form of the "hallucinatory delusions." The German collective investigations record four cases of mania in children.
We will omit describing yet other forms of post influenzal psychoses which are classified under the title Acute Paranoia and Dementia Acuta. The first signs of "general paralysis" have often followed influenza (Althaus).
It is obvious that in numerous patients in whom there was latent mental affection or who were on the borderland influenza caused its final resolution. Since all these patients, in whom, of course, the idiopathic psychosis was merely precipitated by influenza, came into lunatic asylums, the assertion of the alienists that only those who were predisposed became mentally deranged by influenza is not very surprising. Kirn has proposed for those cases the term "pseudo influenza psychosis "; by Bidon they were more accurately termed " idiopathic psychoses becoming evident as the result of the influenza attack."
The post influenzal psychosis, like the initial or prodromal psychosis, is frequently of only short duration. In severe cases it may last for weeks and months. The prognosis, as a rule, is very favorable, corresponding to the acute toxic character of these psychoses. Probably but very few individuals, possessed of a hereditary or neuropathic taint, suffered from permanent mental disturbance after influenza. But many merely became insane rather earlier than they would have done without influenza.