ENCEPHALITIS. — In the absolute sense, the term should indicate exclusively morbid processes of an inflammatory nature affecting the mass of the encephalon, whether in the gray matter (polioencephalitides) or in the white matter (leukoencephalitides or demyelinating e.). In practice, forms in which the causal element may not be infectious and the anatomopathological lesions are not properly those classically associated with inflammation are generically designated by the term e.; in them toxic factors operate, or else the action of a virus is not demonstrable and remains only presumptive; for them, the expression “pseudoencephalitides” or “encephaloses” would be more accurate.
Such uncertainty and inexactness of terminology is an indication of the frequent difficulty of demonstrating the causal element, and of the fact that e. sometimes appears as a secondary manifestation in the course of various infectious morbid processes (direct action of the virus and its toxins), exogenous intoxications (alcohol, lead, medicines, etc.), or endogenous intoxications due to altered metabolism (diabetes, nephritis, gestational toxicoses, avitaminoses, dyse endocrinopathies, etc.). E. may develop in an acute or hyperacute form, so as to cause death within 1–2 days (epidemic e.), or with a chronic course and progressive symptomatology. In relation to the high anatomical and functional dignity of the tissue affected, e. is always accompanied, to a greater or lesser extent, by nervous symptoms (anesthesias and paralyses corresponding to the topography of the foci, particularly in the circumscribed purulent forms of cerebral abscesses), or also by psychic symptoms, with diminution or complete loss of consciousness (v. coma), or partial loss of the various elementary activities that constitute it and of which they are the manifestation (interest, attention, perception, memory, intelligence, will, affectivity), or of moral character. Particular damage is inflicted, in addition to nervous functioning, upon the psychic personality of the individual if e., particularly when associated with meningitis, develops during the fetal and infantile periods of life; in such cases, the encephalon in the process of development suffers damage and developmental arrest, sometimes so slight as to be difficult to demonstrate from the anatomopathological point of view, yet always sufficient to produce true psychoses (v. PRENASTHENIA). Such “mentally handicapped persons” deserve the greatest consideration not only from the medical point of view, but also from the educational, juridical, and moral points of view; they are capable of treatment, partial recovery, and social utilization, albeit on a less elevated scale of values. In adults, whose encephalic development is complete and whose ideational patrimony has been acquired, mental damage of varying severity may occur, dementia (v.), as, for example, dementia (v.).
From the practical point of view (familial, social, pastoral), knowledge of the neuropsychic picture that develops as a sequela of a particular form is of special importance: epidemic or lethargic e. (Economo’s disease), which, in its chronic phase, assumes the form of so-called “postencephalitic parkinsonism.” In it, ocular and extrapyramidal phenomena (strabismus, spasms, hypertonicity of the muscles with slow and impeded movements) and neurovegetative disorders (altered metabolism and endocrine balance) are accompanied by a particular neurastheniform and hysteriform psychic picture, exaggerated emotionality, and a particular slowness and difficulty in understanding, at times an appearance of incomprehension, such as to lead one to regard the individual as affected by catatonia or dementia. On the contrary, in the majority of such patients intelligence is not substantially altered; memory, perception, ideation, and discriminative powers are almost normal, although these activities are performed with characteristic slowness (bradypsychism), similar to that which renders bodily movements slow and laborious. All authors agree in asserting that, however pronounced the cerebral torpor, however delayed the psychic reaction and the capacity to fix new perceptions, however severe the impediment—and consequently the outward expression—of volitional powers and affective manifestations, in postencephalitic parkinsonism there is no genuine mental defect, and therefore no true postencephalitic dementia (G. Moglie, op. cit., p. 660).
