These differing forms of acute focal encephalitis which have been referred to illustrate the chief clinical types of the disease. The most common of them is that occurring in infancy or childhood, after or during one of the acute in fectious diseases. The next type in fre quency is that occurring in adult life as a result of the poison of influenza, chronic alcoholism, or without apparent cause. The least frequent is the type due to traumatism, which more fre griently causes a diffuse inflammation.
The part played by acute focal en cephalitis in the etiology of the cerebral palsies of children is a question of much interest, and is as yet Nvholly undeter mined. Osler believes that certain of the cases of sclerosis and porencephalus may be due to infantile meningo-encephalitis, and thinks that the views advanced by Striimpell have not met with the con sideration which they deserve. J. Lewis Smith suggests that certain cases of in fantile henaiplegia are due to cortical encephalitis induced by the toxin of cerebro-spinal fever. Jacobi favors the view that some cases of cerebral palsy in children, disseminated sclerosis, and bulbar paralysis are results of prenatal or infantile primary inflammation of the brain. The exact relationship, however, between acute focal encephalitis in early life and these forms of paralysis still awaits further pathological evidence.
lt will be noticed that the symptoms of acute focal encephalitis are practically of the same character in the adult as they are in the child, although they are often less marked in the adult, and the residual paralyses and other affections above referred to are likely to be less severe. The reason for these differences in degree probably lies in the natural differences which exist between the com paratively poorly developed fcetal and infantile brain as compared with the matured organ. The brain, being the last organ to develop, during infantile life is softer and relatively more vas cular, due to the larger proportion of water it contains; therefore it is not surprising that acute inflammation is far more frequent in infancy and child hood than during any other period of life.
(b) Acute diffuse non-suppurative en cephalitis presents symptoms which in the acute stage closely- resemble those attending the focal variety. They will, of course, vary with the location, extent, and severity of the inflammatory process. It occurs at any age of life, but the cases are more numerous below the age of twenty, according to the statistics of Knaggs and Brown. This form of cere
bral inflammation may be rapidly fatal, or it may run a subacute course, finally ending in a chronic condition. Com plete recovery is exceedingly rare, but partial recovery is not uncommon. It occurs most frequently after traumatism, as the exciting cause. The cases occur ring in adult life are commonly due to alcohol, syphilis, or traumatism. Cases also occur in which it is impossible to assign a definite cause; but it is prob able that, as infection is an important cause of focal encephalitis, it is also a more or less frequent cause of the dif fuse form of the disease. Although there is little regularity in the appear ance of its symptoms, the onset of acute diffuse non-suppurttive encephalitis is apt to be marked by dull or boring pain in the head, fever with delirium or stupor, local or wide-spread muscular spasm, and sonic form of paresis rapidly increasing to paralysis, usually spastic in character. Mental hebetude, or tor por, appears early, and throughout the disease is a very marked feature. The reflexes are increased in the paralyzed parts. Sensation is affected according to the seat of the lesion. The temperature may be subnormal on the paralyzed side in hemiplegic cases. Optic neuritis, which may be present, is not so frequent as in suppurative meningitis or encepha litis. Localized muscular tremblings frequently occur early, and may be the first symptom. These spastic movements may affect any portion of the body, but more frequently one arm or the muscles of the face and neck. Cases are reported in which there has been incessant spasm of the facial muscles, the tongue, the ocular mnscles, and the muscles of mas tication. With these spastic features general convulsions may occur, which may be repeated. The pupils are con tracted or unequal. If the patient sur vives the acute stage, apathy and stupor become more marked. On arousing the patient great mental degeneration is ap parent. The evacuations are voluntary. The temperature falls and a subnormal rancie is common. The disease runs a course of from a few holirs to five or six weeks. Most cases run several weeks. Some cases partially recover and con tinue to live with chronic conditions of paralysis and mental disease. Certain cases of acute delirious mania exhibit post-mortem the lesions of an acute dif fuse non-suppurative encephalitis.