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Epidemic lethargic encephalitis Economo (encephalitis A): causes, symptoms, diagnosis, treatment
Last reviewed: 05.07.2025
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Economo's epidemic lethargical encephalitis (encephalitis A) was first recorded in 1915 in troops near Verdun and described in 1917 by the Viennese neurologist Economo.
The disease in those years occurred in the form of epidemics that affected many countries of the world. In subsequent years, all cases of the disease remained sporadic. Nowadays, the disease in its typical form is almost never encountered.
Causes of epidemic lethargic encephalitis Economo
The causative agent of epidemic encephalitis has not yet been identified. The disease is slightly contagious.
Symptoms of Economo's Epidemic Lethargical Encephalitis
Clinically and pathomorphologically, epidemic encephalitis can be divided into 2 stages - acute and chronic. The acute stage is characterized by symptoms of an inflammatory nature. The chronic stage has a progressive-degenerative nature. The acute and chronic stages of epidemic encephalitis are separated by a period of time from several months to 5-10 years.
The classic form of epidemic encephalitis in the acute stage begins with a rise in body temperature to 38-39 °C. Moderate headache, vomiting, muscle pain, a feeling of general weakness and other symptoms accompanying acute infectious diseases appear. Catarrhal inflammation of the upper respiratory tract is possible. The febrile period lasts on average about 2 weeks. During this period, neurological symptoms appear. In the foreground are pathognomonic sleep disorders for this disease, expressed in pathological drowsiness. The patient can be woken up, but he immediately falls asleep again, in any position and in a situation unsuitable for sleep. Excessive, irresistible sleep can continue for 2-3 weeks, and sometimes longer. Less often, pathological insomnia occurs, when the patient cannot fall asleep either during the day or at night. Perversion of the normal change of sleep and wakefulness is possible. Insomnia often follows or precedes a period of pathological sleepiness.
The second characteristic sign of the acute stage is damage to the large- and small-cell nuclei of the oculomotor, and less frequently, abducent nerves .the nerve is never completely involved in the process: the functions of individual muscles innervated by this nerve are impaired. Possible ptosis (unilateral or bilateral), diplopia, anisocoria, gaze paralysis (usually vertical), absence of pupillary response to convergence and accommodation with a live reaction to light (reverse Argyll Robertson syndrome). Complaints of blurred vision caused by accommodation paresis or diplopia are common.
Sleep disturbances and oculomotor disorders constitute the classic form of epidemic encephalitis (hypersomnic ophthalmoplegia) described by Economo. However, other neurological manifestations are possible in the acute stage. Vestibular disorders in the form of dizziness accompanied by nausea and vomiting occur somewhat less frequently than oculomotor disorders. Horizontal and rotatory nystagmus are detected in the neurological status. Vestibular disorders appear due to damage to the nuclei of the vestibular nerve. Vegetative symptoms are often noted.
Extrapyramidal symptoms characteristic of the chronic stage of epidemic encephalitis are often noted in the acute stage as well. They may manifest as hyperkinesis (choreoathetosis, myoclonus, athetosis, blepharospasm, gaze spasm), and somewhat less frequently as akinetic-rigid syndrome (akinesis, amimia, muscle rigidity, tendency to catatonia). The occurrence of thalamic, cerebellar and hydrocephalic syndromes, as well as hypothalamic disorders, has been described. The acute stage may be accompanied by pronounced psychosensory disorders (changes in the perception of the shape and color of surrounding objects, visual, olfactory, and auditory hallucinations). In severe cases of epidemic encephalitis, disorders of the frequency and rhythm of breathing, cardiovascular activity, myoclonus of the respiratory muscles, hyperthermia, and impaired consciousness (coma) occur. Death may occur due to cardiac and respiratory failure.
In modern conditions, epidemic encephalitis proceeds atypically, mainly abortively, simulating an acute respiratory infection. Against its background, short-term sleep disorders (drowsiness or insomnia), episodes of diplopia, autonomic dysfunction, hyperkinesis (tics in the muscles of the face and neck), mild transient oculomotor disorders may occur. Vestibular, narcoleptic, epileptiform forms, and epidemic hiccups (episodically occurring myoclonic spasm of the diaphragm muscles over several days) are distinguished as independent.
In the cerebrospinal fluid in the acute stage, most patients show pleocytosis (mainly lymphocytic, 40 cells in 1 μl), a slight increase in protein and glucose content. In the blood, leukocytosis with an increase in the proportion of lymphocytes and eosinophils, and an increase in ESR are detected. Generalized changes are detected on the EEG; slow activity is expressed.
The course of epidemic lethargical encephalitis Economo
The acute stage of epidemic encephalitis can last from 2-4 days to 4 months. Sometimes it ends in complete recovery. A fatal outcome is recorded in 30% of cases. In 35-50% of patients, the acute stage becomes chronic. Often, symptoms characteristic of the chronic stage occur without a preceding clearly expressed acute stage. Residual symptoms and syndromes after the acute stage of epidemic encephalitis include headaches, persistent insomnia, sleep rhythm perversion, asthenoneurotic syndrome, depression, convergence insufficiency, mild ptosis. Children often have hypothalamic disorders (endocrine-metabolic disorders), changes in the psyche and character, and decreased intelligence.
The main clinical manifestation of the chronic stage is Parkinsonism syndrome. Characteristic features are poverty and slowness of movements, amimia, monotonous slurred speech of little expression, pro-, latero- and retropulsion, tendency to maintain a given posture, loss of associated movements that individualize motor skills (acheirokinesis), paradoxical kinesias. Loss of interest in the environment, slowness of mental processes, and importunity are noted. In movement disorders, a significant role is played by tone disorders, usually diffusely increased by the plastic type (extrapyramidal rigidity) in both flexors and extensors, the "cogwheel" phenomenon is noted. Oligo- and bradykinesia are combined with characteristic rhythmic hyperkinesia in the form of fine-swinging tremor in the hands (like "counting coins"). Hyperkinesis in the chronic stage of epidemic encephalitis may also manifest itself as blepharospasm, gaze spasm (oculogyric crises). Secretory and vasomotor disorders (hypersalivation, oily skin, hyperhidrosis) are typical for parkinsonism.
Along with Parkinsonism syndrome, endocrine disorders may develop in the form of adiposogenital dystrophy, infantilism, menstrual irregularities, obesity or cachexia, hyperthyroidism, diabetes insipidus. Changes in character, emotional-volitional sphere usually appear and increase. Mental changes are especially pronounced in children (increased eroticism, aggressiveness, antisocial behavior, morbid pedantry, evening attacks of psychomotor agitation). Rarely, epileptiform syndrome, attacks of pathological sleep (narcolepsy) and cataplexy are encountered in the chronic stage.
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Diagnosis of epidemic lethargic encephalitis Economo
Diagnosis of epidemic encephalitis in the acute stage is quite difficult. The basis for diagnosis is various forms of sleep disorders in combination with psychosensory disorders and symptoms of damage to the nuclei of the oculomotor nerves. The appearance of these symptoms against the background of an increase in body temperature and an "unclear" infectious disease is especially important.
It is necessary to differentiate the acute stage of epidemic encephalitis from serous meningitis. In recent years, MRI of the brain has been able to confirm the diagnosis of epidemic encephalitis with pathological changes in the basal ganglia. However, the specific virus has not yet been identified.
Diagnosis of the chronic stage of epidemic encephalitis is less difficult. The diagnosis is based on the characteristic syndrome of parkinsonism, endocrine disorders of central genesis, and mental changes. The progressive nature of these disorders is important, especially in combination with some residual effects of the acute stage (ptosis, insufficiency of convergence and accommodation).
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