The post-mortem appearances of the diffuse form of acute encephalitis do not differ markedly from the localized form except in the greater extent of the lesion. During its acute stage there are the same macroscopical appearances and the brain is softened. In some cases, in which the inflammatory reaction is less severe and of longer duration, the brain undergoes hardening, which may involve a lobe or an entire hemisphere. In these cases of diffuse inflammation implication of the membranes is not uncommon. In most eases of diffuse encephalitis some degree of softening is the rule. Microscopically during the acute stage the vessels are dilated, capillary hmmor rhages are frequent, and the brain-tis sue is infiltrated with leucocytes, which also distend the perivascular lymphatic sheaths. Compoundgranular cells appear, with secondary degenerative changes in the nerve-cells and axis-cylinders, with active proliferation of the neurog lia. This process progresses at times until the nerve-elements are more or less completely destroyed in the affected area.. In cases where hardening takes place both gray and white substances may be involved, but it has been espe cially marked in the white substance. Pathologically, the hardening is due to increase of the connective tissue, espe cially the vascular connective tissue. In one of the cases collected by Iinaggs and Brown, the white substance of both hemispheres was found very much hard ened, while .the cortical substance was so soft as to be easily washed off by a stream of running water, giving the ap pearance afterward of a plaster cast of the encephalon.
Diagnosis.—The recognition of acute non-suppurative encephalitis during the period of its inception must, in nearly all cases, be attended with difficulty. This is particularly true of cases occur ring in infancy and childhood, where it most frequently occurs as a complication or sequel of some of the acute infectious diseases. Very often it is not until the development of some form of paralysis that the disease is suspected to exis.t, and only the most careful study of each individual case can separate this affec tion from meningitis, with which it is, no doubt, frequently associated. This is especially apt to be true in traumatic cases. In all cases in which, during the progress of some acute general disease cerebral symptoms arise, in which, after a period marked by moderate signs of cerebral irritability, there results a paral ysis out of proportion in severity with the general symptoms which might be expected to be present in meningitis, and, if other obvious exciting causes of the latter can be excluded, the presump tion would be in favor of encelihalitis. While no rule can be made with any degree of certainty, it is probable that premonitory symptoms are far more common and last a longer period in men ingitis before stupor and coma super vene. Photophobia, intolerance of light,
and retraction of the head are often per sistent in meningitis for days and even weeks before the stage of coma is reached. In all recorded cas.es of acute non-suppurative encephalitis the tend ency to dullness, apathy, stupor, or coma is a marked and often early feature. The presence of optic neuritis favors meningitis, while its absence is wholly without diagnostic significance.
The best guide to a correct diagnosis. in cases where this is possible, between acute focal non-suppurative encephalitis and the different forms of meningitis is a careful study, not of any particular symptom-group, but of the entire case. There is no absolutely diagnostic sign by which they can be clinically sepa rated, but a careful review of the onset, course, and succession of the symptoms will afford more valuable information than will any study of particular symp toms. Thus it will be borne in mind that both affections are very rare com plications of the acute infectious dis eases, but that meningitis is the more common; that any' local source of septic infection, rheumatism with endocarditis, adjacent disease of the cranial bones, erysipelas, and septicsemia, more fre frequently cause meningitis; and that after traumatism meningitis usually de velops at once or within two or three days, but the signs of encephalitis usu ally do not appea.r until considerably later. In this connection it may be men tioned that cases of acute encephalitis, from severe concussion upon the op posite side from the point of reception of the injury, have been reported.
In cases running a subacute course the decided mental deterioration with long spells of extreme torpor or even semi comatose states, and persistent spastic paralysis, have been the salient features of certain reported cases of diffuse non suppurative encephalitis. Cases of spas tic hemiplegia and diplegia in children quite frequently will give a history of an initial illness attended by convulsions, coma, and fever, and it is probable that a number of these cases arise from acute non-suppurative encephalitis during in fancy. The same may be said of certain cases of disseminated sclerosis and bulbar paralysis. The trend of opinion seems to favor inflammatory lesions as causa tive of many of the chronic degenera tive diseases of the brain met with in adult life. Further pathological proof is needed to establish the diagnostic features of acute inflammation of the brain in early life. In all cases of in flammation of the brain after trauma tism the possibility of a non-suppura tive diffuse encephalitis should be borne in mind. The diagnosis of the dissemi nated type can at present be little more than conjectural.