Definition.—In the present state of our knowledge, chronic encephalitis may be defined as a term which is used to denote several pathological states, but is applied more especially to cases in which there is great increase in the connective tissue elements, resulting usually in hardening of the brain, with secondary degenerative, nutritic, and functional changes in the nerve-elements, and may rarely produce a state of chronic soften ing,.
Varieties.—The following types may be said to show greater or less degrees of chronic encephalitis.
(a) Terminal stages of cases arising more or less acutely, but resulting in chronic cerebral lesions.
In this class may be included those cases presenting residual symptoms, le sions of focal and diffuse non-suppura tive encephalitis, the zones of dense con nective tissue, proliferation surround ing old cases of embolism,thrombosis,ab scess and tumor, the secondary reactive sclerosis found in cases of spastic paral ysis, and the sclerotic patches of dis seminated sclerosis, insular sclerosis, and the syphilitic forms of the same affect ing the brain often in conjunction with a similar spinal lesion. All of these pathological states are essentially of the nature of a chronic inflammation, and in all of them the vascular connective tissue element predominates, to the im pairment or destruction of the parenchy matous brain-tissue. The symptoma tology of all of the above lesions, of course, differ widely according to the site of the lesions, but the chronic en cephalitis undoubtedly is a factor in these and many more, which readily sug gest themselves to the mind of the student of nervous diseases, in which the sole persistent lesion is a sclerosis which is of undoubted inflammatory origin.
(b) Ch ronic meningo-encephalitis. This is the distinctive lesion of paralytic dementia, and for our knowledge of its minute anatomy we are chiefly indebted to the studies of Bevan Lewis. The brain-cortex and the pia mater are in volved in the process. It may also effect the brain to a considerable depth, varying in different convolutions, and ependymitis is frequently also present. Raymond considers the starting-point of the disease in syphilitic subjects to be in the walls of the capillary blood-vessels of the cortex. Bevan Lewis recognizes three stages to chronic meningo-encepha litis, which he gives as follows: 1. Stage of inflammatory proliferation in the tunica adventitia of the arterioles, with special nuclear proliferation, alterations in the calibre of the vessels, and sec ondary trophic changes in the surround ing tissue. 2. Stage of development of
the lymph-connective system, with de creneration and loss of nerve-cells and fibres. 3. Stag,e of fibrillation of con nective-tissue elements, together with great atrophy of the affected portion of the brain.
On removing the calvarimn, in these cases, it is noticed that the dura is gen erally more or less adherent, the cerebro spinal fluid is increased, the meshes of the pia mater are (edematous and fill up the solei all over the cortex, especially in the motor area and over the postero parietal region. The cortex and mem branes are adherent; so that often the cortex is lacerated on removal of the membranes. Marked atrophy of the con volutions is nearly a constant feature. The cortex is harder than normal. On section the thickness of the cortex is diminished, and in places no clear de markation exists between the gray and white matter. There is ventricular dilatation and granular epenclymitis. All of these changes are especially marked over the frontal and parietal regions.
Pathological findings analogous to the above are also observed in some cases of chronic epilepsy, and in certain types of chronic dementia; but this patho logical combination is so uniform and striking in paralytic dementia that it has been accepted unanimously as the lesion of that disease, and by some writers, in cluding Osler, the term "chronic men ingo-encephalitis" is used as synonymous with "general paralysis of the insane." The symptoms, etiology, diagnosis, prognosis, and treatment of this condi tion need not be referred to here, since they will be found in the description of paralytic dementia, which is here only taken as the most prominent type of chronic meningo-enceplialitis, but not as the sole condition in which this lesion exists.
(c) The consideration of forms of chronic softening due to chronic en cephalitis need scarcely be mentioned, since the evidence upon which their pathology rests is too meagre. The ex istence of such cases has, however, been mentioned by Gowers and others, but the writer has been unable to find the accounts of any post-mortem examina tions bearing upon the subject. The chronic state of diffuse or focal s,uppura tion has been referred to as a sequel to an acute inflammation.