ENCEPHALITIS LETHARGICA, a disease of the brain characterized by coma (sleepy sickness). The virus is unknown. Filtrable organisms have been described and also the transmission of the disease by injection of nervous tissues, but these experi ments are at present inconclusive. The incubation period is esti mated at two weeks. The degree of infectivity must be small. The duration of infectivity and of the persistence of the virus in the body are unknown. Apparently the virus may lie quiescent and return to activity after long periods, since late manifestations have been known to develop after two to four years, sometimes after apparent cure in the intervals. No age is immune to infec tion.
2. In which, in addition to general disturbance, there are various localizations in the central nervous system. The most frequent of these are affections of the third pair of cranial nerves, but no por tion of the nervous system is immune.
3. Mild or so-called abortive cases (formes f rustes) .
The clinical manifestations are very variable and complex and are best classified, according to Walshe's scheme into general and nervous.
I. General: (I) negative, (2) positive.
II. Focal: (I) negative, (2) positive.
The positive symptoms denote exaltation of function due either to irritation of nervous tissue or to a loss of the control exerted normally by the higher centres of the brain ; negative symptoms denote depression or loss of function due principally to destruction of nervous tissue.
The onset of the disease may be sudden or insidious. Occasion ally the onset is extraordinarily sudden, the patient falling asleep almost without warning or sometimes becoming delirious. More frequently it is insidious either with the development of drowsi ness or with more general symptoms. The general symptoms are not in themselves distinguishable from those of other conditions. Headache is common, and nausea and vomiting are frequent with out being very severe. The temperature is very variable. It may be about 102° F. at the onset, falling after a few days, or it may be normal at the onset and rise later in the first week. A persistent rise is a serious sign. Some cases are apyrexial throughout. There is no characteristic eruption. In the mild and abortive types the general condition may suggest influenza and the nature of the ill ness only be recognized long subsequently by the development of characteristic late manifestations. Most cases undoubtedly corn mence with some grade of the characteristic symptoms of lethargy and double vision.
The positive symptoms are represented by restlessness, delirium, acute mania and various degrees of excitement. General convul sions are not common but are usually fatal. Negative symptoms are represented by the characteristic lethargy referred to above.
Among the positive symptoms may be mentioned muscular pains which are occasionally severe and may simulate many dis eases. In the positive group fall also the rigidity, Parkinsonism and the various involuntary movements which are referred to below among the late manifestations. The negative symptoms are represented by paralysis. The ocular manifestations have been mentioned above. Affection of the remaining cranial nerves may produce facial paralysis, difficulty in swallowing, rapid respiration and paralysis of the pharyngeal and laryngeal muscles. Aphasia and paralysis of the limbs may also occur. The deep reflexes are usually absent in the acute stages of severe cases, but there is no constant rule. The cerebrospinal fluid may show a moderate in crease in the number of lymphocytes but in at least one-third of the cases the fluid is normal.
The most important of these manifestations are as follow : The Parkinsonian Syndrome.—This is characterized by the remarkable absence of facial expression which is termed the "Par kinsonian mask." There is also general muscular rigidity and a striking absence of slight and automatic movements. The general appearance resembles the condition known as paralysis agitans though the general effect is not quite identical.
Mental Changes.—These are of great importance from their frequency and character and are present to some extent in about 75% of cases. The changes may be of all grades, from slight weak ness of the intellectual powers to definite dementia and insanity.
In adults the usual manifestation is a general weakness of the intellectual powers. The subject shows a marked lack of attention, concentration and initiative. Definite melancholia is not very common. There may be some irritability of temper but the excite ment 'which occurs in children is not often seen in adults. Insom nia is a not infrequent symptom and may be very persistent. On the other hand there may be persistent drowsiness.
In children the mental changes are far more varied and of greater importance than in adults. As in adults the commonest effect is a weakening of the powers of concentration.
A second group, numerically smaller, is characterized by ex citement. These children are usually under ten years of age. The excitement may be most marked during the night. For the time they are quite beyond control.
This group merges into a third group in which there are definite alterations in the moral character. Most of the children are be tween the ages of ten and 18 years. This group, though small, is important owing to the difficulty in dealing with the subjects. They become morally and sexually perverted. These changes are more common in children of families with a bad record mentally and criminally. There is a small group in which idiocy develops, usually in children under five years of age, and in a few cases there has been definite certifiable insanity. In addition to these mental changes Parkinsonism may be present and also the myoclonic and other movements described below. The treatment and especially the disposal of children in the second and third groups is a mat ter of great difficulty. Home surroundings are rarely suitable and the child will render ordinary family life impossible.
Involuntary Movements.—This group of "excito-motor" symptoms includes numerous varieties of involuntary movements and muscular contractions. Though they are more common late in the disease many of them occasionally occur at the onset. The most definite type is myoclonus which is characterized by short, rapid, rhythmic contractions of the muscles : a single muscle such as the diaphragm, or even a part of a single muscle may be affected. There is generally no movement at the joints, but in some cases the contractions are of a slow, rhythmic type and may lead to very complex movements. Various choreiform and athetoid movements are also met with. Tremors and tics of all types may also develop. Epidemic hiccough may be a variety.
Respiratory Abnormalities.—Rapid or deep breathing may be present, either continuously or in paroxysms at any period of the acuter stages. Violent spasmodic cough occasionally develops in children or sniffing and various respiratory spasms.
Paralysis.—The persistence of these is relatively uncommon. Diplopia is rarely permanent. Many nervous diseases, however, are occasionally simulated such as disseminated sclerosis. Nu merous other late manifestations are observed more rarely. Among these may be mentioned obesity which is occasionally associated with polyuria, suggesting disturbance of the pituitary gland.
Progress and Prognosis.—A. J. Hall states as a rough approxi mation that of 1 oo cases, 25 recover completely, 25 die, and 5o have various residua of which at least 25 exhibit Parkinsonism. It is impossible to give a good prognosis during the acute stages in any case of encephalitis lethargica, owing to the fact that serious late manifestations may develop after a mild initial attack. Fur ther, long quiescent periods may occur with subsequent recru descence of activity and fresh manifestations. Such intervals may be several years, but the limit is at present unknown.
In the acute stages the outlook for life is bad with severe general symptoms, with a rapid onset, with high temperature, with acute delirium or with mania. Slight early symptoms may, how ever, also progress to serious grades. Deep, early lethargy is not necessarily a serious symptom. Early myoclonus and involuntary movements do not appear to be especially unfavourable. Most deaths occur within the first month and the prognosis for life improves after this.
With regard to special manifestations, the Parkinsonian syn drome may be recovered from partially or even completely when it develops early in the disease, but when it appears later it usually progresses and mental changes may also occur. The outlook in the cases with the severer mental changes is poor; recovery is rarely more than partial and relapses may follow.
The influence on pregnancy has been carefully studied by Hall. He considers that there is no evidence that pregnancy predisposes to infection with encephalitis lethargica, or that it is associated with a higher mortality or influences the course of the disease in any way. Residual manifestations, however, may be aggravated in a woman who has passed through an attack and become preg nant subsequently.
Diagnosis.—The disease is often easily recognized from the combination of lethargy and double vision. The milder forms, however, are easily overlooked at the onset and may frequently be unavoidably mistaken for influenza. When the more complex nervous symptoms are present the diagnosis may be of great diffi culty. The conditions with which confusion most often occurs are meningitis (especially tuberculous), cerebral tumour, cerebral vascular lesions and cerebral syphilis.
Treatment.—This is on the general lines of treatment of acute febrile disease. Unfortunately there are no specific measures. The administration of hexamine may be recommended. The with drawal of cerebrospinal fluid by lumbar puncture is frequently performed but there is no evidence that it is beneficial.
(H. L. T.)