ENCEPHALITIS. — Gr., iyxicbcao5, the brnirt, and cri;, inflammation.
Synonyms. —Encephalitis; cerebritis.
Definition.—Inflammation may attack any portion of the brain, and in some cases nearly the entire brain is affected. It is probable that general inflammation of the brain never occurs, death ensuing before the inflammatory process invades the whole brain. "Usually the inflamma tion is confined to a more or less cir cumscribed area in one lobe, but quite frequently it involves an entire lobe, less frequently all of one hemisphere, or large areas of both hemispheres; also it may exist as isolated or disseminated foci throughout the organ. No age of life is exempt from it, and a prenatal form is described. It is also frequently asso ciated with meningitis.
Encephalitis may cause acute or chronic softening, the formation of pus, and complete disintegration of affected parts of the brain; or it may cause an acute or chronic hardening of the brain, with or without atrophy, and, in certain rare cases, hypertrophy may exist. It is thus seen that the term encephalitis covers a wide range of clinical cases, and includes in its symptomatology an al most-endless combination of symptom groups, which depend for their associa tion upon the nature, grade, extent, and location of the inflammation within the encephalon, as well as upon many con comitant conditions which may exist in , the patient. All of the symptom-groups have, however, usually some common characteristics, and, while accuracy in diagnosis is probably nowhere else more difficult, in many of the cases certain types of encephalitis have been de scribed which show considerable uni formity. In the consideration of the subject it seeins better to classify the cases upon what we know of their pathology, meagre as this often is, than to use the many etiological synonyms so frequently found in the older descrip tions. In the present state of our knowl edge certain terms commonly used are misleading to the student. This applies to the terms polioencephalitis superior and polioencephalitis inferior, introduced by 'Wernicke, and also to the polioen cephalitis of Striimpell. These terms are widely used to denote some 1A-ell-known types of focal encephalitis; but, since more recently many cases have been re ported in which focal encephalitis in volved both the gray and white sub stance, it would seem that such syn onyms as proposed by 'Wernicke and Strfimpell only serve to confuse, as re marked by Mills in his recent excellent work upon diseases of the nervous sys tem. Encephalitis is often associated
with meninaitis and the term "menin , go-encephalitis" is applied to inflam- I illation of the membranes and subjacent brain-cortex.
Varieties. — For convenience of de scription encephalitis may be classified as follows:— 1. Acute non-suppurative encepha litis.
(a) Focal.
(b) Diffuse.
(c) Disseminated.
11. Acute suppurative encephalitis.
(a) Focal or circumscribed (ab scess), single or multiple.
(b) Diffuse.
III. Chronic encephalitis.
(a) Terminal stages of cases arising acutely, but resulting in chronic cerebral lesions.
(b) Chronic meningo-encephalitis.
(c) Chronic softening due to en cephalitis.
IV. Prenatal encephalitis.
Acute Non-suppurative Encephalitis.
Acute non-suppurative encephalitis occurs most frequently in infancy and childhood, but may occur at any age. Since the paper of Striimpell in 1884 much interest has been awakened in the whole subject of cerebral inflammation, and a considerable number of cases have been reported in which the autopsies have proved beyond doubt the existence of acute non-suppurative encephalitis as a distinct, primary affection. By some authorities it is held that acute non suppurative encephalitis during fcetal and infantile life is the prime factor in the etiology of a considerable propor tion of cases of chronic degenerative dis eases of the brain, including infantile cerebral paralysis, disseminated sclerosis, and bulbar paralysis. Observations, re corded since 1884, -upon cases present ing the symptoms of acute encephalitis, tend to confirm this view; and it seems to be fairly established tbat acute en cephalitis quite commonly leaves residual affections, especially motor and psychical in character. Certain writers have af firmed a special tendency of acute non suppurative encephalitis to attack the motor regions of the brain; but this may be only seemingly so, because of the great difficulty of observing defects of thc special senses in children. While there are, undoubtedly, certain areas which, when they present an acute in flammation, give us more typical signs of its presence than do many of the so called "silent regions" of the brain, one cannot review the post-mortem records, meagre as they still are, without con cluding that acute inflammation attacks quite impartially the gray and white matter, the cortex and basal ganglia, the lining membrane of the ventricles, and the enveloping membranes of the en cephalon.