Symptoms.—The symptoms of chronic encephalitis will depend upon its vari ety, etiology, location, and the grade of the process, as will readily be appreciated when the wide range of clinical cases in which this lesion exists is considered. Reference has been made to the types described by Hughlings-Jackson and by Gowers, in which more or less severe signs of cerebral irritation existed for months, with slight fever, and sometimes spastic neuritis, especially in those cases having head-pain, vomiting, and focal signs simulating those of tumor.
In all cases in which chronic encepha litis exists as a complicating or reactive inflammatory condition, its symptoms tology is essentially that of the primary condition giving rise to it. This refers to cases of brain-tumor, abscess, em bolism, thrombosis, foreign bodies im planted in the brain, exostoses of the cranial bones inflicting pressure upon the brain, or calcareous growths developed within the cerebral membranes. Chronic encephalitis enters also into the pathol ogy of syphilis and chronic alcoholism.
For the symptoms caused by chronic meningo-encephalitis—or "periencepha litis," as preferred by certain writers— the reader is referred to the article upon paralytic dementia, or general paralysis of the insane; while essentially the same lesions occurring in some cases of chronic epilepsy and of terminal dementia do not give rise to any constant clinical type.
It is thus seen that the study of the clinical symptoms which may arise, upon the pathological basis of chronic en cephalitis are many and varied, and can only be studied as types, some of which have been indicated as most clearly proved to exist as results of an inflam matory lesion.
Etiology. — The primary etiological factor in cases of chronic encephalitis is, excluding syphilitic cases, almost always obscure, and the exact nature of the pri mary irritant, which we must assume as causative, is still a subject for future in vestigation. There is, in certain cases, probably an hereditary predisposition or weakness of the cerebral vascular system, owing to which the changes in the peri vascular connective tissue occur from causes insufficient to produce them in the ordinary brain. This hereditary factor in etiology is hard to prove, but is frequently suggested in the clinical study of the cases.
The obvious predisposing causes of chronic encephalitis are those common to very many diseases of the brain, and include syphilis, embolism, traumatism, excessive physical or mental labor, anxiety or worry, fright, the acute in fectious diseases; organic affections of the kidneys, liver, or heart; and others.
There is little doubt that prolonged mental overwork, especially if associated with prolonged anxiety, is capable of leading to pronounced vascular disturb ance in the cerebrum, thus furnishing the conditions upon which the inflamma tory process may be readily ingrafted.
Pathology.—So far as is known, the primary changes in chronic encephalitis occur in the vascular (mesodermic) con nective tissues, and other structures are coincidently—or, more usually, '1 quent/y—attacked. In syphilitic cases the specific irritant toxin probably acts upon the nerve-cell, the neuroglia, the 2 lymph-connective system, and the vas cular and perivascular tissues; and it is further probable that one or other of these elements suffer more or less in dif ferent cases, and that this explains in some degree the wide range of syphilitic brain-symptoms. It would appear, how ever, that chronic encephalitis from all causes is usually of primary' vascular origin, the pathological and clinical evi dences both supporting this view.
Post-mortem examination in cases of chronic encephalitis reveals most com monly atrophy of the affected part, with hardening of the tissues; very rarely it has revealed hypertrophy of the convolu tions as a result of the inflammation; according to the observations of Gowers, a type of chronic encephalitis exists in which no macroscopical change can be noticed after death, but in which "slight diffuse inflammatory changes were found throughout the brain-substance on mi croscopical examination." In certain other cases the same authority affirms that chronic encephalitis may cause a form of chronic softening, which has already been referred to in this paper.
The microscopical appearances differ according to the stage of the process, and have already been sufficiently re ferred to in describing the varieties of the disease.