Encephalitis lethargica …

Ravindra Kumar Garg DM

General Neurology

Updated 12.28.2024
Released 12.08.2006
Expires For CME 12.28.2027

Encephalitis lethargica

Author: Ravindra Kumar Garg DM

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Editor: John E Greenlee MD

Encephalitis lethargica

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Introduction

Overview

Encephalitis lethargica was a mysterious epidemic disease of the 1920s and 1930s that was better known as the “sleepy” or “sleeping” sickness. Importantly, it was associated with the subsequent development of postencephalitic parkinsonism, a condition that was popularized in Oliver Sacks’s 1973 book, Awakenings, and the 1990 movie of the same name. Encephalitis lethargica evolved to have many manifestations other than a “lethargic type,” including types that were primarily characterized by insomnia or movement disorders. In the acute stage, encephalitis lethargica was characterized by intractable somnolence, which was then attributed to abnormalities of the diencephalon. Since then, anatomical localization of sleep has been focused on the subcortical brain. Differentiating points from idiopathic Parkinson disease include young age of onset, oculogyric crises, altered sleep-wake cycle, respiratory disturbances, and pyramidal signs. A variety of respiratory abnormalities were noted, particularly, unrelenting tachypnoea (panting) without air hunger and an inspiratory hold (fixés en inspiration forcée). These respiratory disorders, in fact, were considered hysterical in nature but later considered serious. Pathologically, there is diffuse involvement of gray matter of the brain dominantly, the diencephalon, and the mesencephalon. There has been extensive debate about the possible role of the “Spanish” H1N1 influenza A pandemic virus in the development of encephalitis lethargica, but this relationship has not yet been established. The role of the substantia nigra and intracellular inclusion bodies (Lewy bodies) in the pathogenesis of idiopathic Parkinson disease was based on observations of severe nigral pathology in encephalitis lethargica. A review of 614 patient records from a UK hospital, diagnosed with encephalitis lethargica from 1918 to 1946, showed unique neuropsychiatric symptoms and weak evidence for infectious or occupational links, as well as possible autoimmune encephalitis links. No definite treatment for encephalitis lethargica is available. The prognosis is variable. Many of the survivors have permanent neurologic sequelae, and some are completely akinetic.

Key points

	• Encephalitis lethargica is an acute polio-encephalitis of largely unknown etiology.
	• Encephalitis lethargica can only be diagnosed clinically.
	• Oculogyric crises were not associated with acute cases during the epidemic period. Oculogyric crises are characterized by sudden, simultaneous, and prolonged deviation of the eyes, often in an upward direction.
	• Differentiating points from Parkinson disease are a young age of onset, oculogyric crises, altered sleep cycle, respiratory disturbances, and pyramidal signs.
	• Putative cases have linked the hyperkinetic form of the condition with NMDAR-Ab encephalitis.
	• Although no clear data link encephalitis lethargica with influenza, such a linkage is still supported by some data and some clinicians.

Historical note and terminology

On April 17, 1917, at a meeting of the Vienna Society for Psychiatry and Neurology, Dr. Constantin von Economo described a new disease, encephalitis lethargica (71). Shortly thereafter, von Economo published his first article on the disease (70). He described a series of cases in which the patients exhibited “a kind of sleeping sickness” with an unusually prolonged course. Headache and malaise were the first symptoms, followed by somnolence, often associated with delirium, from which the patient could be easily awakened. This state could rapidly lead to death or could persist for long periods, either progressing to coma or ending with recovery. These signs were generally accompanied by paralysis in some of the cranial nerves, especially those affecting the eye. Ptosis was a typical sign. Von Economo concluded that he believed the disease was an “encephalitis,” with the variability relating to variations in neural localization of the causative agent.

The disease then began appearing in increasing frequency throughout the world, with official figures showing peaks of about 10,000 cases in 1920 and 1924 (46), with a possible total mortality of 500,000 cases (49) during the entire epidemic period, which lasted until about 1940. Sporadic reports of encephalitis lethargica cases have continued to appear since then.

During the epidemic period, the signs and symptoms of the disease rapidly increased so that eventually 28 “types” were described, with signs and symptoms encompassing virtually every neurologic system (63), including some that were antithetical to von Economo’s original description (eg, an “insomnia” type). Kroker convincingly argued that curing encephalitis lethargica became the foremost aim of American neurology (especially New York City neurologists) during this period and that the secondary goal of this effort was to significantly increase the prominence and potential of American neurology (35). Thus, there may have been some political aspects to the large number of encephalitis lethargica diagnoses. This possible overdiagnosis was also noted during the epidemic period (27).

Wijdicks and Boes studied respiratory rhythm abnormalities reported in patients with epidemic encephalitis (encephalitis lethargica). The authors focused their extensive literature search on disorders of respiration rate, respiratory patterns, and respiratory tics. The respiratory abnormalities most frequently noted included unrelenting tachypnoea (panting) without air hunger and an inspiratory hold (fixés en inspiration forcée). These respiratory disorders, in fact, were previously considered hysterical in nature but later were considered serious. Wijdicks and Boes considered these respiratory disorders part of a parkinsonian syndrome and taught that these attacks could have been provoked by oxygen therapy (72).

Even after 100 years, many issues related to encephalitis lethargica remain elusive. Authors are still struggling to answer the questions: what causes it? How is this disease transmitted? Could an epidemic of encephalitis lethargica happen again? (31; 59). Encephalitis lethargica garnered attention for its impact on consciousness and a potential link to postencephalitic Parkinsonism. Although once considered sporadic, some reviews suggest it might be an autoimmune response to a viral agent, possibly a coronavirus. Historical epidemics like Russian influenza and Spanish flu showed similar neurologic symptoms. Interestingly, some COVID-19 cases present resemblances to encephalitis lethargica (22).

Rogers and co-workers conducted a study to investigate the presentation and possible causes of encephalitis lethargica, a rare neurologic disease (50). They analyzed the case notes of 614 patients diagnosed with the disease at a UK hospital between 1918 and 1946. The patients had a median age of 29 years and a median time since symptomatic onset of 3 years. The most common symptoms were motor features, present in 97.6% of patients, followed by cranial nerve findings, ophthalmological features, sleep disorders, gastrointestinal or nutritional features, speech disorders, and psychiatric features. The authors compared the clinical presentation of the patients to modern diagnostic criteria for encephalitis lethargica, catatonia, and autoimmune encephalitis. They found that 276 patients, or 45% of the total, might meet the criteria for possible autoimmune encephalitis, but only three patients, or 0.5%, might meet the criteria for probable NMDA receptor encephalitis. The authors also investigated possible environmental and infectious causes of the disease. They found that 195 patients, or 31.8%, had a history of febrile illness within 1 year prior to illness onset, which was more common than among the controls. However, the evidence for a link between the disease and infectious or environmental exposures was weak.

On the centenary of Tretiakoff's landmark thesis on the morphology of Parkinson disease, it was argued that the crucial involvement of the substantia nigra and the role of intracellular inclusion bodies (Lewy bodies) in the pathogenesis of idiopathic Parkinson disease may, in fact, have originated from the findings of dominant nigral pathology in patients with encephalitis lethargica (32). Tretiakoff's selective focus on the substantia nigra was likely influenced by the widespread prevalence of epidemic encephalitis lethargica during his era, which frequently presented with characteristic nigral pathology. This historical context underscores how the understanding of Parkinson disease evolved from the pathological insights gained during an epidemic, paving the way for subsequent confirmation and refinement of these findings in later decades.

Clinical manifestations

Presentation and course

Encephalitis lethargica is a highly polymorphic disease that tends to appear in epidemic outbreaks, with signs and symptoms fluctuating to some degree from one epidemic to another. The most common prodromal symptoms are headache, slight sore throat, chilly sensations, general weakness, and mild gastrointestinal disturbances. The most prominent signs are lethargy, sleepiness, or stupor both at the onset and through at least the early stages of the disease. This lethargy may be more apparent than real, however, as the patient is conscious of passing stimuli and, once aroused, immediately becomes alert and sensible (“false sleep” or “pseudo somnolence”). In contrast, the patient may exhibit insomnia, alone or alternating with somnolence. Sometimes, patients exhibit delirium. Paralyses or pareses, most often associated with the cranial nerves, result in oculomotor abnormalities (eg, diplopia, ptosis, accommodation paralysis, sluggish pupils, strabismus, nystagmus), facial paralyses, masticatory paralyses, dysphagia, or dysarthria, and occasionally there are paralyses of the trunk or limbs. Some patients develop parkinsonian rigidity, catatonic stupor, and catalepsy. Other patients show hyperkinetic phenomena, including myoclonias, “fascicular twitchings,” epileptiform convulsions, choreic movements, and maniacal states. Some patients experience sensory disturbances, including pain (eg, headache, facial, muscular). Isolated cases of a cerebellar type of ataxia have been reported. The CSF is generally normal or has a slightly increased cell count (06; 73).

The mortality rates for encephalitis lethargica varied greatly with time and geography. Between 1919 and 1927, in New York City and England, the annual rate varied from 29% to 75%. Although encephalitis lethargica was typically not considered to be contagious, there were some well-researched instances in which the condition did appear to spread from person to person (61).

Encephalitis lethargica could also be complicated by severe changes in behavior, particularly in children.

Encephalitis lethargica in a young boy

Observe abnormal posture of flexed body, retracted upper limbs, forward head lean, and open mouth. (Contributed by Dr. Joel A. Vilensky.)

Von Economo said of children with encephalitic lethargica in his 1931 monograph, “We see here how organic encephalitic lesions may produce in previously normal individuals a strange alteration of personality, which cannot be otherwise described than as a kind of moral insanity or erethic imbecility.” Von Economo continued to note that these children “annoy strangers on the street, pluck their clothing, make faces at them or abuse them; they tramp, beg, lie, steal, write on the walls, squander all the money they can lay hands on in sweets, cannot be controlled at school, run away from home and spend their time at the cinema and in the streets, indulge in sexual misbehaviour of every kind and make other dangerous acts” (71). Except in the very young, there was no deterioration of intellect (11). The pejorative term “Apache” was used to characterize these children, referring to the wild behavior attributed to Apache Indians (27). Hill estimated that, whereas 70% of pediatric encephalitic lethargica survivors showed some psychological changes, approximately one third exhibited behavioral disorders (29). In the acute phase, encephalitis lethargica was characterized by intractable somnolence, which was then attributed to abnormalities of the diencephalon. This indicated that sleep mechanisms are localized in the subcortical brain (39).

Encephalitis lethargica was often complicated by lingering or permanent somatic or psychological sequelae, the most serious of which was postencephalitic parkinsonism (23). Postencephalitic parkinsonism could develop within a short time of the original episode, after a number of symptomatic changes, or even months or years (in some cases many years) after symptoms have purportedly disappeared. The hallmark features of postencephalitic parkinsonism comprise rigidity, tremor, dysarthria, flexed postures, and masked facies (73). The best differentiators of postencephalitic parkinsonism from idiopathic parkinsonism are onset below middle age, symptoms lasting more than 10 years, presence of oculogyric crises, and palilalia (30; 36).

Oculogyric crisis

Young adult woman with oculogyric crisis. Observe the typical combination of torticollis and forced upward and lateral eye movements with a flexed posture of the right upper limb. Oculogyric crises were typically associated with p...

Other features that Hoehn and Yahr considered uncommon in the idiopathic form but common in postencephalitic parkinsonism include oculomotor and other cranial nerve palsies, pyramidal tract signs, dystonic phenomena, sleep disturbances, personality changes, and autonomic dysfunction (30).

The presumptive direct relationship between encephalitis lethargica and postencephalitic parkinsonism has been questioned (61; 62). These authors noted that careful analysis of the historical data indicated that many (perhaps, the majority) of persons with postencephalitic parkinsonism did not have a prior well-defined encephalitic disease but often had had a condition (eg, influenza) that was diagnosed post hoc as encephalitis lethargica. Based on these data, it has been thought that the relationship between encephalitis lethargica and parkinsonism is more complex than perceived, ie, that encephalitis lethargica alone was not responsible for the subsequent development of parkinsonism.

Prognosis and complications

Whereas some patients appear to show a complete recovery, others show persisting somatic impairments (eg, movement disorders) or psychological impairments (eg, behavioral disorders, especially in children). Postencephalitic parkinsonism was believed to be a sequel in up to 80% of affected individuals (23).

Clinical vignette

One of the most well-known cases of encephalitis lethargica was that of Patricia Maguire, who was also known as Oak Park’s (Illinois) “sleeping beauty.” In January 1932, 27-year-old Patricia began feeling increasingly drowsy each day. After falling asleep on a train, she returned home and slumbered fitfully for 9 days and then, on February 24, became comatose. After about a year and a half, she began to show signs of consciousness with open eyes, alert expressions, and the ability to respond to simple commands, although her eyes did not respond to light, and she could not speak. Unfortunately, these positive signs did not last, and she again became comatose. Maguire died of pneumonia in 1937. Her brain was removed after death and revealed an atrophied frontal lobe, which was believed to confirm a diagnosis of encephalitis lethargica.

Although no good images of Patricia Maguire are available, there are many still and moving images of patients with encephalitis lethargica (67). German neuropsychiatrists Karl Kleist and Ernst Herz made a detailed film (13 minutes) of one young patient, and a segment of that film is available here.

Encephalitis lethargica in a young adult male

Observe open-mouth posture and tongue and upper limb tremors. (Contributed by Dr. Joel A. Vilensky.)

Biological basis

Etiology and pathogenesis

At the time of the epidemic, various bacterial or viral causes were proposed for the condition, but no definitive findings were reached. There has been extensive debate about a possible role of the “Spanish” H1N1 influenza A pandemic virus in the development of encephalitis lethargica (55). Modern efforts to demonstrate influenza RNA segments in the brains of encephalitis lethargica victims, however, have not been successful (41; 37). Nevertheless, these results are far from conclusive, so there remains a possibility that a recurrence of bird-based influenza will result in a recurrence of encephalitis lethargica (42; 40), which advocates that influenza did cause encephalitis lethargica. Foley exhaustively examined the historical record pertaining to the relationship between encephalitis lethargica and influenza and concluded that, whereas any individual feature of encephalitis lethargica could be found in influenza, the combination of symptoms was unique, suggesting that encephalitis lethargica was not likely caused by influenza (25; 26; 20).

Although a viral etiology has always been suspected in postencephalitic parkinsonism, no definitive infectious agent has been isolated. Several case reports suggested that infection with atypical enterovirus can result in postencephalitic parkinsonism and a picture similar to encephalitis lethargica (01; 56). Evidence for encephalitis lethargica's autoimmune nature is also limited, suggesting it may have been a unique response to an unknown pathogen in genetically susceptible individuals. Contemporary autoimmune encephalomyelitis cases, though increasing, differ significantly from historical encephalitis lethargica in symptoms, epidemiology, and pathology (13).

In three cases, parkinsonism has been described following SARS-COV-19 infection. In these cases, a viral invasion of the brainstem, in these cases, has been speculated (15; 24; 44). However, the possibility of SARS-CoV-2 causing an encephalitis lethargica-like state remains speculative (05; 28). Morassi and colleagues described two isolated cases of SARS-CoV-2-related encephalitis with prominent parkinsonism (45). FDG-PET/CT findings in these patients were consistent with postencephalitic parkinsonism. FDG-PET/CT demonstrated the presence of cortical hypometabolism along with hypermetabolism in the regions of the brainstem, mesial temporal lobes, and basal ganglia.

Dale and colleagues attempted to determine the cause of encephalitis lethargica by identifying 20 new cases of encephalitis lethargica in England between 1999 and 2002; 11 of the patients had preceding pharyngitis (17). They then investigated the possibility that the patients’ phenotype could be a postinfectious autoimmune CNS disorder, similar in that respect to Sydenham chorea. Western immunoblotting showed that 19 of the patients had autoantibodies reactive against human basal ganglia antigens. The authors concluded that an encephalitis lethargica-like syndrome is still prevalent and that encephalitis lethargica may be secondary to autoimmunity against deep gray matter neurons resulting from a prior group A Streptococcus infection (ie, a PANDAS disease) (17). The conclusions of Dale and colleagues were then questioned in a 2004 editorial in Brain, which noted that only a minority of the cases had two of the more diagnostic signs of encephalitis lethargica: ophthalmoplegia and oculogyric crises (69). Additional criticism can be found in a study by Singer and colleagues, who took serum from patients in three groups (patients with PANDAS, patients with Tourette syndrome, and age-matched controls). ELISA and Western blots against crude soluble extracts of postmortem brain regions and Western blots against putative antigens were performed. Antibodies were found for all groups, but there were no differences in antibody frequencies between patient groups and controls (51). According to Vernino, these results cast doubt on the role of neurologic antibodies in these pediatric neuropsychiatric movement disorders but do not exclude an immune-mediated (or even antibody-mediated) etiology for these diseases (and presumably for encephalitis lethargica) (60).

Encephalitis lethargica may have been an autoimmune encephalitis associated with antineuronal antibodies, many of which were unknown at the time, including anti-NMDAR antibodies. The occurrence of encephalitis lethargica during the 1918 influenza pandemic raises the possibility that the virus triggered antineuronal immune responses through mechanisms such as molecular mimicry or immune dysregulation, as seen in other viral infections like herpes simplex virus and Japanese encephalitis, both known to induce anti-NMDAR antibodies. Sera from 10 of 20 pediatric patients with suspected encephalitis lethargica were found to be positive for NMDAR antibodies, presenting with dyskinesias, insomnia, and seizures (18). Additionally, studies identified encephalitis lethargica–like features in young females with ovarian teratomas who tested positive for NMDAR antibodies in serum and CSF. These findings suggest that the dyskinetic (hyperkinetic) form of encephalitis lethargica may represent NMDAR antibody-mediated encephalitis, even in very young children. Armangue and colleagues further demonstrated that post-herpes simplex encephalitis, NMDAR antibody synthesis occurred within weeks, often preceding neurologic relapse, with most patients responding to immunotherapy (04). In the absence of sera or CSF to test retrospectively (neither sera nor CSF from encephalitis lethargica patients in earlier series is available for study), the presence of autoantibodies in patients cannot be determined, and it is possible that more than one antineuronal antibody (eg, anti-AMPAR or other antibodies besides anti-NMDAR) could have been involved, possibly explaining the diverse clinical features of encephalitis lethargica.

It is unclear whether the findings of Dale and colleagues (18) mean that the different forms of encephalitis lethargica had different etiologies (eg, the dyskinetic form had a different cause than the lethargic form), a hypothesis supported in a book about encephalitis lethargica (62). Since the 2009 report by Dale and colleagues, other case studies have appeared supporting a relationship between the dyskinetic (hyperkinetic) form of encephalitis lethargica and NMDAR-Ab encephalitis (47; 54).

This summary of the pathology of encephalitis lethargica is based primarily on the 1921 review of encephalitis lethargica by CP Symonds, a prominent British neurologist (53). The described pathology is only for encephalitis lethargica; the pathology associated with postencephalitic parkinsonism is not described here; for that, see (57; 34).

The gross fresh brain of an encephalitis lethargica victim shows little abnormality beyond congestion of the meningeal and intracerebral capillaries. This congestion causes the brain to be reddish in color in cross-section, and the cut vessels are widely open and oozing bright blood.

Microscopic examination of the preserved brain indicates that the most important features are vascular congestion, signs of toxic degeneration of neurons and neuronophagia, proliferation of vessel wall cells, infiltration of the perivascular (Virchow-Robin) spaces with small round cells, and glial proliferation. Degenerative loss of neurons in nuclei is variable; when present, the degenerating cells exhibit swelling and eccentricity of the nucleus, chromatolysis, and neuronophagia.

Symonds stressed that the brain of a patient who dies rapidly from encephalitis lethargica might show little pathology, perhaps only vascular congestion. Symonds accounted for this observation by noting that cellular function may be lost before any visible structural alterations. He also reported that the distribution of lesions varies greatly from patient to patient, although more lesions appear within the midbrain and basal ganglia than elsewhere. Others, however, indicated that cortical damage was frequent and basal ganglia damage rather infrequent (07). Our own analysis of 112 acute cases from the epidemic period suggests that about 80% showed cortical damage, whereas only about 40% showed basal ganglia damage (03).

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References

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Contributors

All contributors' financial relationships have been reviewed and mitigated to ensure that this and every other article is free from commercial bias.

Author

Ravindra Kumar Garg DM

Dr. Garg of King George's Medical University in Lucknow, India, has no relevant financial relationships to disclose.
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Editor

John E Greenlee MD

Dr. Greenlee of the University of Utah School of Medicine has no relevant financial relationships to disclose.
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Former Authors

Joel A Vilensky PhD

Patient Profile

Age range of presentation: 0 month to 65+ years
Sex preponderance: male>female, >1:1
Heredity: none
Population groups selectively affected: none selectively affected
Occupation groups selectively affected: none selectively affected

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Encephalitis lethargica

Associated Disorders

epidemic influenza
postencephalitic parkinsonism
sleeping sickness

Differential Diagnosis

somnolence
sleep inversion
insomnia
lethargy
ophthalmoplegia
- parkinsonism
- dyskinesias
- neuropsychiatric symptoms
- oculogyric crises

Also Relevant

Catatonia
Diplopia
Hypersomnolence
Insomnia
Oromandibular dystonia
- Sleep disorders
- Sleep and medical disorders
- Sleeping sickness

Encephalitis lethargica …

Encephalitis lethargica

Introduction

Overview

Key points

Historical note and terminology

Clinical manifestations

Presentation and course

Prognosis and complications

Clinical vignette

Biological basis

Etiology and pathogenesis

Epidemiology

Prevention

Differential diagnosis

Confusing conditions

Table 1. Diagnostic Criteria of Encephalitis Lethargica

Diagnostic workup

Management

Special considerations

Pregnancy

Media

References

Contributors

Author

Editor

Former Authors

Patient Profile

ICD & OMIM codes

This is an article preview.
Start a Free Account
to access the full version.

Questions or Comment?

Also in This Category

Neurologic manifestations of celiac disease and gluten sensitivity

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Prognosis after cardiac arrest

Neuromodulation

Diplopia

Isolated sixth nerve palsy

Polyneuropathy associated with anti-MAG IgM antibodies

Radial neuropathy

(1) Recent influenza-like manifestations (08) (2) Hypersomnolence (3) Wake-ability (easy to rouse) (4) Ophthalmoplegia (more than one)
	• Ptosis • Strabismus • Diplopia • Weakness of convergence • Nystagmus • Unequal pupils • Defective reactions to light • Defective reaction on convergence and accommodation • Argyll Robertson pupils
(5) Psychiatric changes (6) Other conditions have been excluded

Encephalitis lethargica

Introduction

Overview

Key points

Historical note and terminology

Clinical manifestations

Presentation and course

Prognosis and complications

Clinical vignette

Biological basis

Etiology and pathogenesis

Epidemiology

Prevention

Differential diagnosis

Confusing conditions

Table 1. Diagnostic Criteria of Encephalitis Lethargica

Diagnostic workup

Management

Special considerations

Pregnancy

Media

References

Contributors

Author

Editor

Former Authors

Patient Profile

ICD & OMIM codes

This is an article preview. Start a Free Account to access the full version.

Questions or Comment?

Also in This Category

Neurologic manifestations of celiac disease and gluten sensitivity

Use of focused ultrasound in neurologic disorders

Prognosis after cardiac arrest

Neuromodulation

Diplopia

Isolated sixth nerve palsy

Polyneuropathy associated with anti-MAG IgM antibodies

Radial neuropathy

This is an article preview.
Start a Free Account
to access the full version.