Etiology of acute childhood encephalitis at The Hospital for Sick Children, Toronto, 1994-1995

Long-term motor and cognitive outcome of acute encephalitis

OBJECTIVES

To examine the long-term motor and neurocognitive outcome of children with acute encephalitis and to look at possible prognostic factors.

METHODS

Children who were treated for acute encephalitis in 2000-2010 were reevaluated. All children and their parents were interviewed by using structured questionnaires, and the children underwent full neurologic examinations, along with comprehensive neurocognitive, attention, and behavioral assessments.

RESULTS

Of the 47 children enrolled, 1 died and 29 had neurologic sequelae, including motor impairment, mental retardation, epilepsy, and attention and learning disorders. Children with encephalitis had a significantly higher prevalence of attention-deficit/hyperactivity disorder (50%) and learning disabilities (20%) compared with the reported rate (5%-10%) in the general population of Israel (P < .05) and lower IQ scores. Lower intelligence scores and significantly impaired attention and learning were found even in children who were considered fully recovered at the time of discharge. Risk factors for long-term severe neurologic sequelae were focal signs in the neurologic examination and abnormal neuroimaging on admission, confirmed infectious cause, and long hospital stay.

CONCLUSIONS

Encephalitis in children may be associated with significant long-term neurologic sequelae. Significant cognitive impairment, attention-deficit/hyperactivity disorder, and learning disabilities are common, and even children who were considered fully recovered at discharge may be significantly affected. Neuropsychological testing should be recommended for survivors of childhood encephalitis.

Case definitions, diagnostic algorithms, and priorities in encephalitis: consensus statement of the international encephalitis consortium

BACKGROUND

Encephalitis continues to result in substantial morbidity and mortality worldwide. Advances in diagnosis and management have been limited, in part, by a lack of consensus on case definitions, standardized diagnostic approaches, and priorities for research.

METHODS

In March 2012, the International Encephalitis Consortium, a committee begun in 2010 with members worldwide, held a meeting in Atlanta to discuss recent advances in encephalitis and to set priorities for future study.

RESULTS

We present a consensus document that proposes a standardized case definition and diagnostic guidelines for evaluation of adults and children with suspected encephalitis. In addition, areas of research priority, including host genetics and selected emerging infections, are discussed.

CONCLUSIONS

We anticipate that this document, representing a synthesis of our discussions and supported by literature, will serve as a practical aid to clinicians evaluating patients with suspected encephalitis and will identify key areas and approaches to advance our knowledge of encephalitis.

Variability in the Diagnosis of Encephalitis by Pediatric Subspecialists: The Need For a Uniform Definition

Research definitions of encephalitis vary widely. When surveyed on the criteria used in clinical diagnosis, 88 pediatric specialists demonstrated diverse responses, with pediatric neurologists and pediatric infectious disease specialists differing significantly in their consideration of cerebrospinal fluid pleocytosis and abnormal neuroimaging. Results emphasize the need for a uniform definition.

Encephalitis

Encephalitis is a serious and potentially treatable infection of the central nervous system. A pathogen is identified in less than 50% of cases. The differential diagnosis includes acute infection, immune-mediated causes, and other central nervous system processes. Emergent investigations include blood work, cerebrospinal fluid analysis, and neuroimaging. Empiric acyclovir and antibiotics should be started immediately to maximize the child's chance of neurologic recovery.

Molecular epidemiological study of enteroviruses associated with encephalitis in children from India

Enteroviruses have been reported in encephalitis cases. However, clinical and epidemiological characteristics of enteroviruses in encephalitis are not fully established. We prospectively investigated 204 children with encephalitis over a period of 2 years (2009 to 2010) for enterovirus. Enterovirus was detected in 45 specimens (22.1%); of these, 40 were typed by seminested reverse transcription-PCR (RT-PCR) and sequencing of the VP1 gene. Molecular typing of enterovirus revealed the predominance of echovirus 21 associated with an epidemic during the rainy seasons of 2010 and the circulation of echovirus 1, coxsackievirus B1, enterovirus 75, enterovirus 76, coxsackievirus B5, and echovirus 19. The nucleotide divergence among echovirus 21 strains was 0 to 2% at the nucleotide level. This study suggests that enterovirus is an important cause of encephalitis in children from India. To our knowledge, this is the first report of echovirus 21 in encephalitis cases worldwide.

Management of suspected viral encephalitis in children - Association of British Neurologists and British Paediatric Allergy, Immunology and Infection Group national guidelines

In the 1980s the outcome of patients with herpes simplex encephalitis was shown to be dramatically improved with aciclovir treatment. Delays in starting treatment, particularly beyond 48 h after hospital admission, are associated with a worse prognosis. Several comprehensive reviews of the investigation and management of encephalitis have been published. However, their impact on day-to-day clinical practice appears to be limited. The emergency management of meningitis in children and adults was revolutionised by the introduction of a simple algorithm as part of management guidelines. In February 2008 a group of clinicians met in Liverpool to begin the development process for clinical care guidelines based around a similar simple algorithm, supported by an evidence base, whose implementation is hoped would improve the management of patients with suspected encephalitis.

Potential risk factors associated with human encephalitis: application of canonical correlation analysis

BACKGROUND

Infection of the CNS is considered to be the major cause of encephalitis and more than 100 different pathogens have been recognized as causative agents. Despite being identified worldwide as an important public health concern, studies on encephalitis are very few and often focus on particular types (with respect to causative agents) of encephalitis (e.g. West Nile, Japanese, etc.). Moreover, a number of other infectious and non-infectious conditions present with similar symptoms, and distinguishing encephalitis from other disguising conditions continues to a challenging task.

METHODS

We used canonical correlation analysis (CCA) to assess associations between set of exposure variable and set of symptom and diagnostic variables in human encephalitis. Data consists of 208 confirmed cases of encephalitis from a prospective multicenter study conducted in the United Kingdom. We used a covariance matrix based on Gini's measure of similarity and used permutation based approaches to test significance of canonical variates.

RESULTS

Results show that weak pair-wise correlation exists between the risk factor (exposure and demographic) and symptom/laboratory variables. However, the first canonical variate from CCA revealed strong multivariate correlation (ρ = 0.71, se = 0.03, p = 0.013) between the two sets. We found a moderate correlation (ρ = 0.54, se = 0.02) between the variables in the second canonical variate, however, the value is not statistically significant (p = 0.68). Our results also show that a very small amount of the variation in the symptom sets is explained by the exposure variables. This indicates that host factors, rather than environmental factors might be important towards understanding the etiology of encephalitis and facilitate early diagnosis and treatment of encephalitis patients.

CONCLUSIONS

There is no standard laboratory diagnostic strategy for investigation of encephalitis and even experienced physicians are often uncertain about the cause, appropriate therapy and prognosis of encephalitis. Exploration of human encephalitis data using advanced multivariate statistical modelling approaches that can capture the inherent complexity in the data is, therefore, crucial in understanding the causes of human encephalitis. Moreover, application of multivariate exploratory techniques will generate clinically important hypotheses and offer useful insight into the number and nature of variables worthy of further consideration in a confirmatory statistical analysis.

Anti-N-methyl-D-aspartate receptor encephalitis: a newly recognized inflammatory brain disease in children

OBJECTIVE

Anti-N-methyl-D-aspartate receptor (anti-NMDAR) encephalitis is a newly recognized antineuronal antibody-mediated inflammatory brain disease that causes severe psychiatric and neurologic deficits in previously healthy children. The present study was undertaken to describe characteristic clinical features and outcomes in children diagnosed as having anti-NMDAR encephalitis.

METHODS

Consecutive children presenting over a 12-month period with newly acquired psychiatric and/or neurologic deficits consistent with anti-NMDAR encephalitis and evidence of central nervous system (CNS) inflammation were screened. Children were included in the study if they had confirmatory evidence of anti-NMDAR antibodies in the serum and/or cerebrospinal fluid. Features at clinical presentation and results of investigations were recorded. Type and duration of treatment and outcomes at last followup were documented.

RESULTS

Seven children were screened, and 3 children with anti-NMDAR encephalitis were identified. All patients presented with neurologic and/or psychiatric abnormalities, seizures, speech disorder, sleep disturbance, and fluctuating level of consciousness. The 2 older patients had more prominent psychiatric features, while the younger child had significant autonomic instability and prominent involuntary movement disorder. None had an underlying tumor. Immunosuppressive therapy resulted in near or complete recovery; however, 2 of the patients had early relapse necessitating re-treatment.

CONCLUSION

Anti-NMDAR encephalitis is an important cause of neuropsychiatric deficits in children, which must be included in the differential diagnosis of CNS vasculitis and other inflammatory brain diseases. Early diagnosis and treatment are essential for neurologic recovery.

Causes of encephalitis and differences in their clinical presentations in England: a multicentre, population-based prospective study

BACKGROUND

Encephalitis has many causes, but for most patients the cause is unknown. We aimed to establish the cause and identify the clinical differences between causes in patients with encephalitis in England.

METHODS

Patients of all ages and with symptoms suggestive of encephalitis were actively recruited for 2 years (staged start between October, 2005, and November, 2006) from 24 hospitals by clinical staff. Systematic laboratory testing included PCR and antibody assays for all commonly recognised causes of infectious encephalitis, investigation for less commonly recognised causes in immunocompromised patients, and testing for travel-related causes if indicated. We also tested for non-infectious causes for acute encephalitis including autoimmunity. A multidisciplinary expert team reviewed clinical presentation and hospital tests and directed further investigations. Patients were followed up for 6 months after discharge from hospital.

FINDINGS

We identified 203 patients with encephalitis. Median age was 30 years (range 0-87). 86 patients (42%, 95% CI 35-49) had infectious causes, including 38 (19%, 14-25) herpes simplex virus, ten (5%, 2-9) varicella zoster virus, and ten (5%, 2-9) Mycobacterium tuberculosis; 75 (37%, 30-44) had unknown causes. 42 patients (21%, 15-27) had acute immune-mediated encephalitis. 24 patients (12%, 8-17) died, with higher case fatality for infections from M tuberculosis (three patients; 30%, 7-65) and varicella zoster virus (two patients; 20%, 2-56). The 16 patients with antibody-associated encephalitis had the worst outcome of all groups-nine (56%, 30-80) either died or had severe disabilities. Patients who died were more likely to be immunocompromised than were those who survived (OR = 3·44).

INTERPRETATION

Early diagnosis of encephalitis is crucial to ensure that the right treatment is given on time. Extensive testing substantially reduced the proportion with unknown cause, but the proportion of cases with unknown cause was higher than that for any specific identified cause.

FUNDING

The Policy Research Programme, Department of Health, UK.

Viral etiology of encephalitis in children in southern Vietnam: results of a one-year prospective descriptive study

BACKGROUND

Acute encephalitis is an important and severe disease in children in Vietnam. However, little is known about the etiology while such knowledge is essential for optimal prevention and treatment. To identify viral causes of encephalitis, in 2004 we conducted a one-year descriptive study at Children's Hospital Number One, a referral hospital for children in southern Vietnam including Ho Chi Minh City.

METHODOLOGY/PRINCIPAL FINDINGS

Children less than 16 years of age presenting with acute encephalitis of presumed viral etiology were enrolled. Diagnostic efforts included viral culture, serology and real time (RT)-PCRs. A confirmed or probable viral causative agent was established in 41% of 194 enrolled patients. The most commonly diagnosed causative agent was Japanese encephalitis virus (n = 50, 26%), followed by enteroviruses (n = 18, 9.3%), dengue virus (n = 9, 4.6%), herpes simplex virus (n = 1), cytomegalovirus (n = 1) and influenza A virus (n = 1). Fifty-seven (29%) children died acutely. Fatal outcome was independently associated with patient age and Glasgow Coma Scale (GCS) on admission.

CONCLUSIONS/SIGNIFICANCE

Acute encephalitis in children in southern Vietnam is associated with high mortality. Although the etiology remains unknown in a majority of the patients, the result from the present study may be useful for future design of treatment and prevention strategies of the disease. The recognition of GCS and age as predictive factors may be helpful for clinicians in managing the patient.

Long-term outcomes of acute encephalitis in childhood

OBJECTIVES

The aims of this study were to investigate the long-term outcomes of childhood encephalitis and to examine possible prognostic factors.

METHODS

Of 93 children who were treated for acute encephalitis in 2000-2004, 71 were eligible for follow-up evaluations. A structured interview, using 2 questionnaires, was conducted with the parents. Fifteen of the children with the most-severe symptoms at the time of discharge also underwent electroencephalographic recording and tests of reaction times and working memory.

RESULTS

Persisting symptoms were reported by 54% of children. The predominant symptoms were personality changes and cognitive problems. Children who made a complete recovery did so within 6 to 12 months. The only significant risk factor for sequelae was disease severity leading to admission to the ICU. The risk of subsequent epilepsy was increased for children with seizures at presentation. Most follow-up electroencephalograms showed improvement, but results had not normalized for 9 of 15 children. Children with encephalitis had slower reaction times, compared with control subjects, but no difference in working memory could be seen.

CONCLUSION

Persisting symptoms after childhood encephalitis were present for a substantial number of children. Seizures increased the risk of subsequent epilepsy; the only other prognostic marker was admission to the ICU. Even children who were considered fully recovered at discharge reported persisting symptoms at follow-up evaluations. Children who made a full recovery did so within 6 to 12 months, which suggests that all children with encephalitis should be monitored for 1 year after the acute illness.

Analysis of status epilepticus with Mycoplasma pneumoniae encephalitis

Encephalitis is characterized clinically by fever, seizure, and an altered level of consciousness. Mycoplasma pneumoniae, a common respiratory pathogen, has been implicated as an etiology of encephalitis. The present study was designed to analyze status epilepticus associated with M. pneumoniae encephalitis in a series of children through retrospective review of cases between January 2002 and January 2008. Systematic clinical data were evaluated. Nine patients were identified: five girls and four boys, aged 4 years to 10 years. All were positive for M. pneumoniae by serology. Six of the nine children (67%) developed refractory status epilepticus. The major clinical symptoms included fever (100%) and upper respiratory symptoms (78%). The most common seizure type was primary focal with secondary generalized seizure (44%). The time of follow-up for this study ranged from 18 months to 86 months. At the end of the study period, two patients had died, seven had developed epilepsy or neurologic deficits, and none had returned to baseline. These data indicate that children with status epilepticus associated with M. pneumoniae encephalitis have high mortality and morbidity. Clinicians should be aware of the potential role of M. pneumoniae in status epilepticus.

Causality in acute encephalitis: defining aetiologies

Defining the causal relationship between a microbe and encephalitis is complex. Over 100 different infectious agents may cause encephalitis, often as one of the rarer manifestations of infection. The gold-standard techniques to detect causative infectious agents in encephalitis in life depend on the study of brain biopsy material; however, in most cases this is not possible. We present the UK perspective on aetiological case definitions for acute encephalitis and extend them to include immune-mediated causes. Expert opinion was primarily used and was supplemented by literature-based methods. Wide usage of these definitions will facilitate comparison between studies and result in a better understanding of the causes of this devastating condition. They provide a framework for regular review and updating as the knowledge base increases both clinically and through improvements in diagnostic methods. The importance of new and emerging pathogens as causes of encephalitis can be assessed against the principles laid out here.

Advances in pediatric neurovirology

Viral infections of the pediatric central nervous system (CNS) encompass a broad spectrum of both perinatally and postnatally acquired diseases with potentially devastating effects on the developing brain. In children, viral infections have been associated with chronic encephalopathy, encephalitis, demyelinating disease, tumors, and epilepsy. Older diagnostic techniques of biopsy, viral culture, electron microscopy, gel-based polymerase chain reaction (PCR), and viral titer quantification are being replaced with more rapid, sensitive, and specific real-time and microarray-based PCR technologies. Advances in neuroimaging technologies have provided for earlier recognition of CNS injury without elucidation of specific viral etiology. Although the mainstay therapy of many pediatric neurovirologic diseases, aside from HIV, includes intravenous acyclovir, much work is being done to develop novel antiviral immunotherapies aimed at both treating and preventing pediatric CNS viral disease.

Evidence and rationale for the World Health Organization recommended standards for Japanese encephalitis surveillance

BACKGROUND

Japanese encephalitis (JE) is the most important form of viral encephalitis in Asia. Surveillance for the disease in many countries has been limited. To improve collection of accurate surveillance data in order to increase understanding of the full impact of JE and monitor control programs, World Health Organization (WHO) Recommended Standards for JE Surveillance have been developed. To aid acceptance of the Standards, we describe the process of development, provide the supporting evidence, and explain the rationale for the recommendations made in the document.

METHODS

A JE Core Working Group was formed in 2002 and worked on development of JE surveillance standards. A series of questions on specific topics was initially developed. A literature review was undertaken and the findings were discussed and documented. The group then prepared a draft document, with emphasis placed on the feasibility of implementation in Asian countries. A field test version of the Standards was published by WHO in January 2006. Feedback was then sought from countries that piloted the Standards and from public health professionals in forums and individual meetings to modify the Standards accordingly.

RESULTS

After revisions, a final version of the JE surveillance standards was published in August 2008. The supporting information is presented here together with explanations of the rationale and levels of evidence for specific recommendations.

CONCLUSION

Provision of the supporting evidence and rationale should help to facilitate successful implementation of the JE surveillance standards in JE-endemic countries which will in turn enable better understanding of disease burden and the impact of control programs.

Immediate relief of Mycoplasma pneumoniae encephalitis symptoms after intravenous immunoglobulin

Mycoplasma pneumoniae may cause acute encephalitis, resulting in severe neurologic complications despite antibiotic therapy. We report the case of a 12-year-old patient who presented with acute onset of orofacial tics, motor restlessness, compulsive behavior, and cerebellar symptoms. Cerebrospinal fluid examination demonstrated lymphocytic meningitis. Polymerase chain reaction for M. pneumoniae was strongly positive in the cerebrospinal fluid. Blood and cerebrospinal fluid were negative for M. pneumoniae antibodies (immunoglobulin M and immunoglobulin G). The child was administered intravenous gamma-globulin, which led to a dramatic improvement of her clinical condition and disappearance of the symptoms within 72 hours. This novel case points to the potential value of gamma-globulin in M. pneumoniae encephalitis confirmed with polymerase chain reaction and suggests that immediate administration of intravenous gamma-globulin in suspected mycoplasma encephalitis should be investigated in a larger patient cohort.

A prospective multicenter study of childhood encephalitis in Greece

Encephalitis is associated with significant childhood morbidity and mortality worldwide, however not much is known about the contemporary epidemiology and outcome. In this prospective multicenter pediatric encephalitis study conducted in Greece for 3 years, 42 cases were diagnosed and the presumptively or definitely causative pathogen was identified in 24 (57.1%). Leading pathogens included herpes viruses (10 patients), enteroviruses (6), and Streptococcus pneumoniae (2). No fatalities were observed; however, deficits remained in 5 of 42 (11.9%) children.

Sensitive, qualitative detection of human herpesvirus-6 and simultaneous differentiation of variants A and B

BACKGROUND

The current limitations of laboratory testing for the detection of human herpesvirus virus 6 (HHV-6) in clinical specimens with low HHV-6 viral loads make this area a priority for further research and development.

OBJECTIVES

To develop and validate a sensitive qualitative assay for simultaneous HHV-6 detection and variant differentiation.

METHODS

We developed a diagnostic procedure, which combines a magnetic bead-based nucleic acid extraction, PCR amplification, and colorimetric microtiter plate identification (MAG-PCR-EIA), for the sensitive detection of HHV-6 and the simultaneous differentiation of HHV-6A and HHV-6B.

RESULTS

Analytic sensitivities of the MAG-PCR-EIA assay were 10 copies per reaction for both HHV-6A and HHV-6B variants, which is equivalent to 20 copies/ml when 1ml of clinical specimen was processed. A proficiency panel containing 11 blinded specimens covering HHV-6A viral loads from 0 to 100,000 copies was tested, and the MAG-PCR-EIA was able to detect the lowest concentration at one copy in 200microl. A panel of 27 urine specimens, which were collected from patients with and without chronic fatigue syndrome, was tested by the MAG-PCR-EIA. HHV-6 was detected in two (HHV-6A) patients who have chromosomally integrated HHV-6A and in one (HHV-6B) patient who was a healthy control and diagnosed as cervical cancer later on. The HHV-6 results did not correlate with results previously determined by HHV-6 antigenemia in urine.

CONCLUSION

With large specimen volumes processed and an additional signal amplification incorporated, the MAG-PCR-EIA provides a sensitive and qualitative system for HHV-6 detection and simultaneous variant differentiation. Clinical relevance of the assay awaits further investigation.

Echovirus type 9 is an important cause of viral encephalitis among infants and young children in Kuwait

BACKGROUND

The role of enteroviruses in encephalitis is not fully established.

OBJECTIVE

This study determined the role of enteroviruses in encephalitis in neonates, infants and young children in Kuwait.

STUDY DESIGN

Cerebrospinal fluid (CSF) samples obtained from 147 patients presenting with 'severe encephalitis' (n=60), 'mild encephalitis' (n=43), and febrile seizures (n=44) over a 3.5-year period, were analyzed. Enteroviral RNA was detected by one-step reverse transcription-PCR (RT-PCR) assay and specific enteroviruses were identified by sequencing a variable region of the enteroviral genome.

RESULTS

Enteroviral RNA was detected in 29 of 103 (28%) samples obtained from encephalitis patients but only in 8 of 44 (18%) samples from patients with febrile seizures. Echovirus type 9 (E9) was detected in 24 of 29 (83%) while E30 was found in 5 of 29 (17%) of enterovirus-positive encephalitis cases. Two of 8 (25%) cases of febrile seizures were infected with E9. The E9 viral load was higher in patients with 'severe encephalitis' than in patients with 'mild encephalitis' or in patients with febrile seizures. All but one enteroviral encephalitis case had a complete recovery.

CONCLUSIONS

Enteroviruses, especially E9 are an important cause of encephalitis among neonates, infants and young children in Kuwait.

Powassan encephalitis and Colorado tick fever

This article discusses two tick-borne illnesses: Powassan encephalitis, a rare cause of central nervous system infection caused by the Powassan virus, and Colorado tick fever, an acute febrile illness caused by the Colorado tick fever virus common to the Rocky Mountain region of North America.

Childhood encephalitis in Sweden: etiology, clinical presentation and outcome

Acute encephalitis is a relatively uncommon but potentially harmful CNS inflammation usually caused by infection. The diagnosis is difficult to establish and the etiology often remains unclear. Furthermore, the long-term prognosis of acute encephalitis in children is poorly described. In this study, we characterize childhood encephalitis from a Swedish perspective in regard to etiology, clinical presentation and sequele. We retrospectively studied all children (n=93) who were admitted for acute encephalitis at Karolinska University Hospital in Stockholm during 2000-2004. A confirmed etiological agent was identified in eight cases and a probable one in 37; in 48 cases no etiological agent could be found. Tick-borne encephalitis virus, enterovirus, respiratory syncytial virus, varicella zoster virus and influenza virus predominated and represented 67% of all the confirmed or probable etiologies. Encephalopathy was present in 80% of the children, 81% had fever, 44% had focal neurological findings, and seizures occurred in 40%. EEG abnormalities were seen in 90% and abnormal neuroimaging was present in 30%. The cerebrospinal fluid showed pleocytosis in 55%. There was no mortality, but 60% of the children had persisting symptoms at the time of discharge, 41% of which were moderate to severe. We conclude that the etiology of encephalitis among Swedish children is at large the same as in other European countries with similar vaccination programs. Fever and encephalopathy were seen in a majority of children and the most sensitive tool for making the diagnosis was EEG examination. Furthermore, many children display persisting sequele at discharge for which the strongest predictive factor was focal neurological findings at presentation.

The incidence of acute encephalitis syndrome in Western industrialised and tropical countries

Background

As part of efforts to control Japanese encephalitis (JE), the World Health Organization is producing a set of standards for JE surveillance, which require the identification of patients with acute encephalitis syndrome (AES). This review aims to provide information to determine what minimum annual incidence of AES should be reported to show that the surveillance programme is active.

Methods

A total of 12,436 articles were retrieved from 3 databases; these were screened by title search and duplicates removed to give 1,083 papers which were screened by abstract (or full paper if no abstract available) to give 87 papers. These 87 were reviewed and 25 papers identified which met the inclusion criteria.

Results

Case definitions and diagnostic criteria, aetiologies, study types and reliability varied among the studies reviewed. Amongst prospective studies reviewed from Western industrialised settings, the range of incidences of AES one can expect was 10.5–13.8 per 100,000 for children. For adults only, the minimum incidence from the most robust prospective study from a Western setting gave an incidence of 2.2 per 100,000. The incidence from the two prospective studies for all age groups was 6.34 and 7.4 per 100,000 from a tropical and a Western setting, respectively. However, both studies included arboviral encephalitis, which may have given higher rather than given higher] incidence levels.

Conclusion

In the most robust, prospective studies conducted in Western industrialised countries, a minimum incidence of 10.5 per 100,000 AES cases was reported for children and 2.2 per 100,000 for adults. The minimum incidence for all ages was 6.34 per 100,000 from a tropical setting. On this basis, for ease of use in protocols and for future WHO surveillance standards, a minimum incidence of 10 per 100,000 AES cases is suggested as an appropriate target for studies of children alone and 2 per 100,000 for adults and 6 per 100,000 for all age groups.

Acute neurological events associated with influenza vaccination: are the WHO criteria for assessing causality adequate?

We identified neurological admissions temporally associated with influenza vaccine to determine the likelihood of causality using World Health Organization (WHO) criteria. Although all cases were categorized as possibly related to the vaccine, most had a compelling alternative explanation. This observation suggests that the current WHO criteria may not be sufficient in determining if an adverse event is truly vaccine related.

Role of Mycoplasma pneumoniae in pediatric encephalitis

A retrospective study investigating all the infectious encephalitis cases hospitalized at the pediatric intensive care unit of Edouard Herriot University Hospital in Lyon, France, was carried out in order to estimate the prevalence of Mycoplasma pneumoniae in acute childhood encephalitis. From January 2001 to December 2005, the cases of 29 children were selected and reviewed. M. pneumoniae related encephalitis was considered as probable in five cases (17%) on the basis of positive serological tests or positive polymerase chain reaction (PCR) tests in throat or nasopharyngeal swab while the PCR tests performed from the cerebrospinal fluid were negative. This study suggests that M. pneumoniae may be a major cause of infectious encephalitis in children as well as enteroviruses or Epstein-Barr virus detected in five and three cases, respectively.

Acute childhood encephalitis and encephalopathy associated with influenza: a prospective 11-year review

BACKGROUND

Influenza virus infection has been associated with a variety of neurologic complications. The objective of this study was to evaluate prospectively the role of influenza viruses in acute childhood encephalitis/encephalopathy (ACE).

METHODS

All children admitted to the Hospital for Sick Children, Toronto, during an 11-year period with ACE and evidence of acute influenza virus infection were included. Acute influenza virus infection was defined by detection of the organism in the nasopharynx by direct immunofluorescence microscopy or viral culture and/or by a 4-fold or greater rise in complement fixation titer.

RESULTS

A total of 311 children with ACE were evaluated; evidence of influenza infection was detected in 7% (22 of 311). Eight were excluded from the main analysis because of evidence implicating other potential pathogens. Eleven of the 14 included subjects were <5 years of age. A respiratory prodrome was documented in 93% of subjects. In 64% neurologic manifestations developed within 5 days of onset of respiratory symptoms. Neuroimaging abnormalities were more common in children <2 years of age. Neurologic sequelae occurred in more than one-half of subjects.

CONCLUSIONS

In this prospective registry, influenza virus infection was associated with 5% of ACE cases. The majority of children were <5 years of age and the prevalence of neuroimaging abnormalities was higher in children <2 years of age suggesting that younger children are predisposed to the neurologic complications of influenza. An acute rather than a postinfectious process was suggested by the briefness of the respiratory prodrome in most cases.

The epidemiology of acute encephalitis

Encephalitis means inflammation of the brain matter. Despite being a rare condition, encephalitis is of public health importance worldwide because it has high morbidity and mortality. Yet, many details about its epidemiology have yet to be elucidated. This review attempts to summarise what is known about the epidemiology of the infective causes of encephalitis and is based on a literature search of the Medline archives. Infection is the most common cause identified, with viruses being the most important known aetiological agents. Incidence varies between studies but is generally between 3.5 and 7.4 per 100,000 patient-years. Encephalitis affects peoples of all ages; however, incidence is higher in the paediatric population. Although both sexes are affected, most studies have shown a slight predominance in males. Encephalitis occurs worldwide; some aetiologies have a global distribution (herpesviruses) while others are geographically restricted (arboviruses). Although definite epidemiological trends are evident, it is difficult to make generalisations as few population-based studies exist, most cases are not reported to health authorities, and many possible pathogens are implicated but in most cases a cause is never found. A better understanding of the epidemiology of this devastating disease will pave the way for better prevention and control strategies.

Pediatric encephalitis: what is the role of Mycoplasma pneumoniae?

BACKGROUND

Encephalitis is a complex, debilitating, and sometimes fatal neurologic condition to which children are especially prone. Mycoplasma pneumoniae, a common respiratory pathogen, has been implicated as an etiology of encephalitis. Evidence for recent or acute M. pneumoniae infection has been demonstrated in limited studies of both pediatric and adult patients with encephalitis.

PATIENTS AND METHODS

Unexplained encephalitis cases are referred to the California Encephalitis Project for diagnostic testing. Serum, cerebrospinal fluid, and respiratory specimens are tested by polymerase chain reaction and serology methods for the presence of multiple pathogens, including M. pneumoniae. M. pneumonia-associated cases of encephalitis were compared with other bacterial agents, herpes simplex virus 1, and enterovirus.

RESULTS

Of 1988 patients referred to the California Encephalitis Project, evidence of acute M. pneumoniae infection was found in 111 patients, of which 84 (76%) were pediatric patients. Eighty percent of the 84 patients were positive for M. pneumoniae by serology alone. Cerebrospinal fluid polymerase chain reaction for M. pneumoniae was rarely positive (2%). Patients with M. pneumoniae-associated pediatric encephalitis were a median of 11 years old, progressed rapidly (median: 2 days from onset to hospitalization), and were often in the ICU (55%). Symptoms included fever (70%), lethargy (68%), and altered consciousness (58%). Gastrointestinal (45%) and respiratory (44%) symptoms were less common. Compared with patients with other bacterial as well as viral agents, patients with M. pneumoniae-associated encephalitis had fewer seizures and less-severe hospital courses.

CONCLUSIONS

M. pneumoniae is the most common agent implicated in the California Encephalitis Project. Patients with M. pneumoniae-associated encephalitis are predominantly pediatric, and their presentations are clinically similar to enterovirus encephalitis, although they frequently require intensive care with prolonged hospitalizations. Given that M. pneumoniae infection is found more than any other pathogen, increased emphasis should be placed on elucidating the role and mechanism of M. pneumoniae in encephalitis.

Risk of serious neurologic disease after immunization of young children in Britain and Ireland

OBJECTIVE

We sought to investigate the risk of serious neurologic disease after immunization in early childhood.

METHODS

The results of a 3-year prospective study of children (2-35 months old) in Britain and Ireland with encephalitis and/or severe illness with convulsions and fever were linked to each child's vaccine history. Cases were reported via the British Paediatric Surveillance Unit's network. The self-controlled case-series method was used to investigate associations between immunization and acute potential adverse events. The risk periods investigated were 0 to 3 and 0 to 7 days post-diphtheria, tetanus, whole cell pertussis, Haemophilus influenzae type b or meningococcal C conjugate vaccine and 6 to 11 and 15 to 35 days post-measles, mumps, rubella vaccine.

RESULTS

A total of 157 disease episodes from 155 children met the analytical case definition. There were 11 cases of herpes simplex encephalitis and 23 cases of primary human herpesvirus 6 and/or 7 infection. There was no evidence of a raised relative incidence of serious neurologic disease in any of the specified risk periods with the exception of a raised relative incidence of 5.68 in the 6-11 days after measles, mumps, rubella vaccine. Based on this relative incidence, between 3 and 6 of the 6 cases in this period were estimated to be attributable to the vaccine with a best estimate of 5. The 6 cases all had fever with convulsions lasting >30 minutes; in all but 1, there was complete recovery by discharge from hospital. Of the 5 patients who recovered, 1 had a concurrent primary human herpesvirus 6 infection and one a primary human herpesvirus 7.

CONCLUSIONS

Six to 11 days after measles, mumps, rubella vaccine there is an increased risk of fever and convulsions lasting >30 minutes. All 6 of the episodes temporally related to immunization met the criteria for complex febrile convulsions. The estimated attributable risk of serious neurological disease was similar to that previously found for measles vaccine.

Diagnostic approaches for patients with suspected encephalitis

Encephalitis represents a diagnostic challenge, with an infectious etiology identified in only 40% to 70% of cases. More than 100 agents have been either definitively or anecdotally associated with encephalitis. Important considerations for diagnosis include selection of the appropriate clinical specimen (serum vs cerebrospinal fluid), determining the most sensitive diagnostic assay (serology vs polymerase chain reaction), and assessing causality when an organism is identified outside of the central nervous system (eg, a positive nasal swab for influenza). This review aims to provide an evidence-based, clinically relevant approach to the diagnostic evaluation of patients presenting with encephalitis, focusing on the most common or important causes in the immunocompetent host. Diagnostic issues associated with encephalitis due to herpes-group viruses, arboviruses (including West Nile virus), rickettsiae, bartonella, enteroviruses, and rabies are discussed in-depth. Diagnostic testing should be individualized based on clinical presentation and epidemiology.

Trends in encephalitis-associated deaths in the United States

The United States national mortality statistics and HIV/AIDS surveillance data were analysed to determine trends in encephalitis-associated deaths and to assess the impact of HIV infection on those deaths during 1979-1998, a period when ICD-9 codes were used for coding deaths in the United States. A total of 25125 encephalitis deaths were reported; 4779 of them (19%) had concurrent HIV infection. Overall encephalitis death rates remained stable, but they increased for groups where HIV infection was common and declined or remained unchanged for others. For persons without HIV infection, the rates declined in all demographic groups. Encephalitis deaths in HIV-infected persons followed general trends for HIV deaths in the United States. The rates in the HIV-infected population were several hundred- to thousand-fold higher than in the HIV-uninfected population. HIV infection was largely responsible for the lack of overall decline in the considerable mortality associated with encephalitis in the United States during 1979-1998.

A 12-year prospective study of childhood herpes simplex encephalitis: is there a broader spectrum of disease?

OBJECTIVE

The purpose of this study was to review the experience with herpes simplex encephalitis at the Hospital for Sick Children over the past 12 years.

METHODS

All patients who were admitted to our institution with acute encephalitis between January 1994 and December 2005 were enrolled prospectively in an encephalitis registry. Children from the registry with herpes simplex encephalitis were included in this study; we detailed the clinical presentations, laboratory findings, electroencephalographic findings, diagnostic imaging findings, treatments, and outcomes for all cases.

RESULTS

Of 322 cases of acute encephalitis, 5% were caused by herpes simplex virus. Initially negative herpes simplex virus cerebrospinal fluid polymerase chain reaction results were found in 2 cases (13%), but results became positive in repeat cerebrospinal fluid analyses. Classic clinical presentations were seen in 75% of cases, cerebrospinal fluid pleocytosis was found in 94%, elevated cerebrospinal fluid protein levels were found in 50%, electroencephalographic changes were observed in 94%, and diagnostic imaging abnormalities were noted in 88%. All patients were treated with intravenous acyclovir. Neurologic sequelae occurred in 63% of cases, including seizures in 44% and developmental delays in 25%. There were no deaths in this study group.

CONCLUSIONS

Herpes simplex encephalitis continues to be associated with poor long-term neurologic outcomes despite appropriate therapy. Cerebrospinal fluid polymerase chain reaction results may be negative early in the course of herpes simplex encephalitis; therefore, repeat cerebrospinal fluid analysis should be considered if herpes simplex encephalitis is suspected. Atypical forms of herpes simplex virus central nervous system disease may occur in children.

Beyond viruses: clinical profiles and etiologies associated with encephalitis

BACKGROUND

Encephalitis is a complex syndrome, and its etiology is often not identified. The California Encephalitis Project was initiated in 1998 to identify the causes and further describe the clinical and epidemiologic characteristics of encephalitis.

METHODS

A standardized report form was used to collect demographic and clinical data. Serum, cerebrospinal fluid, and respiratory specimens were obtained prospectively and were tested for the presence of herpesviruses, arboviruses, enteroviruses, measles, respiratory viruses, Chlamydia species, and Mycoplasma pneumoniae. The association between an identified infection and encephalitis was defined using predetermined, organism-specific criteria for confirmed, probable, or possible causes.

RESULTS

From 1998 through 2005, a total of 1570 patients were enrolled. Given the large number of patients, subgroups of patients with similar clinical characteristics and laboratory findings were identified. Ten clinical profiles were described. A confirmed or probable etiologic agent was identified for 16% of cases of encephalitis: 69% of these agents were viral; 20%, bacterial; 7%, prion; 3%, parasitic; and 1%, fungal. An additional 13% of cases had a possible etiology identified. Many of the agents classified as possible causes are suspected but have not yet been definitively demonstrated to cause encephalitis; these agents include M. pneumoniae (n=96), influenza virus (n=22), adenovirus (n=14), Chlamydia species (n=10), and human metapneumovirus (n=4). A noninfectious etiology was identified for 8% of cases, and no etiology was found for 63% of cases.

CONCLUSIONS

Although the etiology of encephalitis remains unknown in most cases, the recognition of discrete clinical profiles among patients with encephalitis should help focus our efforts toward understanding the etiology, pathogenesis, course, and management of this complex syndrome.

Childhood encephalitis in Crete, Greece

This study included all 18 cases of children hospitalized for encephalitis in the referral university hospital of Heraklion, Crete, Greece, during the 5-year period from 2000 to 2004. Encephalitis was attributed to viral infection (echovirus, herpes simplex virus 1, varicella-zoster virus, cytomegalovirus, and influenza A) in eight children and to bacteria (Mycoplasma pneumoniae, group A beta-hemolytic streptococcus, and Rickettsia typhi) in a further five cases. Multiple hyperintense brain lesions on magnetic resonance imaging (MRI) were associated with a severe clinical presentation but not with a guarded long-term outcome. Five children still presented with mild to moderate sequelae after 1.5 to 5.3 (median 4.0) years. Our findings confirm the elimination of measles, mumps, and rubella-associated encephalitis in the postvaccine era. MRI appeared to be of great diagnostic value. Although no fatalities were observed, deficits did persist in several patients.

Mycoplasma pneumoniae central nervous system infections

PURPOSE OF REVIEW

Mycoplasma pneumoniae is associated with a wide range of central nervous system diseases, most importantly with childhood encephalitis. This review summarizes and discusses recent findings in the field of M. pneumoniae central nervous system infections in context with previously published findings, with reference to clinical spectrum, pathogenesis, diagnosis, and treatment.

RECENT FINDINGS

Further insight into the pathogenesis has been provided by studies on cytokine production and autoantibody formation. Some new manifestations have been described (e.g. Kluver-Bucy syndrome, intracranial hypertension). Anecdotal descriptions on the association of M. pneumoniae with uncommon neurologic diseases remain to be confirmed by additional reports, however, especially when aetiologic diagnosis relied exclusively on serology. New knowledge on treatment options targeting the immune system has been provided by isolated reports. Recent diagnostic advances refer to general methods (polymerase chain reaction, serology), without specific reference to neurologic disease.

SUMMARY

M. pneumoniae must be considered as causative agent of various neurologic diseases. The recent literature shows, however, that the clinical spectrum of M. pneumoniae central nervous system disease is still not well defined. In addition, the main future challenges are the investigation of the pathogenesis of M. pneumoniae central nervous system disease and the establishment of therapeutic approaches.

Mycoplasma pneumoniae-associated myelitis: a comprehensive review

Myelitis is one of the most severe central nervous system complications seen in association with Mycoplasma pneumoniae infections and both acute transverse myelitis (ATM) as well as acute disseminated encephalomyelitis (ADEM) have been observed. We reviewed all available literature on cases of Mycoplasma spp. associated ATM as well as ADEM with dominant spinal cord pathology and classified those cases according to the strength of evidence implicating M. pneumoniae as the cause. A wide range of data on diagnosis, epidemiology, immunopathogenesis, clinical picture, laboratory diagnosis, neuroimaging and treatment for this rare entity is presented. The use of highly sensitive and specific molecular diagnostic techniques may assist in clearly elucidating the role of M. pneumoniae in ATM/ADEM syndromes in the near future. Immunomodulating therapies may have a role in treating such cases.

Pediatric Epstein-Barr virus-associated encephalitis: 10-year review

Many neurologic manifestations of Epstein-Barr virus (EBV) infection have been documented, including encephalitis, aseptic meningitis, transverse myelitis, and Guillain-Barré syndrome. These manifestations can occur alone or coincidentally with the clinical picture of infectious mononucleosis. Since 1994, The Hospital for Sick Children has maintained a prospective registry of all children admitted with acute encephalitis. This report summarizes all cases of Epstein-Barr virus-associated encephalitis compiled from 1994 to 2003. Twenty-one (6%) of 216 children, median age 13 years (range 3-17 years), in the Encephalitis Registry were identified as having evidence of Epstein-Barr virus infection. This evidence consisted of convincing Epstein-Barr virus serology and/or positive cerebrospinal fluid polymerase chain reaction (PCR). One patient had symptoms of classic infectious mononucleosis; all others had a nonspecific prodrome, including fever (n = 17; 81%) and headache (n = 14; 66%). Slightly less than half (n = 10; 48%) had seizures and often had electroencephalograms showing a slow background (n = 12; 57%). Many demonstrated cerebrospinal fluid pleocytosis (n = 17; 81%), and 71% (n = 15) had abnormal magnetic resonance imaging findings. Two patients died, 2 suffered mild deficits, and 16 were neurologically normal at follow-up. Most patients with Epstein-Barr virus encephalitis do not show typical symptoms of infectious mononucleosis. Establishing a diagnosis of Epstein-Barr virus encephalitis can be difficult, and, consequently, a combination of serologic and molecular techniques should be used when investigating a child with acute encephalitis. Most children make full recoveries, but residual neurologic sequelae and even death can and do occur.

Central nervous system manifestations of Mycoplasma pneumoniae infections

Mycoplasma pneumoniae infection is associated with several manifestations from the central nervous system (CNS) such as encephalitis, aseptic meningitis, acute transverse myelitis, stroke, and polyradiculopathy. In the current paper epidemiologic, clinical, laboratory and treatment data on these manifestations are reviewed. The M. pneumoniae induced immune dysregulation and its contributing role in the pathogenesis of neurological insult is discussed. The recent introduction in clinical practice of newer molecular diagnostic techniques has helped in establishing a firmer association between M. pneumoniae infection and CNS disease especially encephalitis. Clinicians should be aware of the potential association between M. pneumoniae infection and several CNS manifestations. The role of various anti-microbial or immunomodulating therapies in treating such manifestations should be further explored.

Prevalence of herpes simplex virus (types 1 and 2), varicella-zoster virus, cytomegalovirus, and human herpesvirus 6 and 7 DNA in cerebrospinal fluid of Middle Eastern patients with encephalitis

HSV-1 DNA was detected in 32 (30%) of 106 cerebrospinal fluid samples from patients with encephalitis. Cytomegalovirus, varicella-zoster virus, and human herpesvirus 6 (HHV-6) DNAs were each detected in three patients (3%); herpes simplex virus type 2 (HSV-2) and HHV-7 PCRs were negative. HSV detection was associated with seizure (P = 0.02), especially focal seizure (P = 0.0002), and pathological computed tomography (P = 0.02) with focal lesions (P = 0.0004).

Diagnosis, treatment, and prognosis of Mycoplasma pneumoniae childhood encephalitis: systematic review of 58 cases

Most of the knowledge on Mycoplasma pneumoniae encephalitis in children is based on case reports or small case series. The aim of this study was to assess the important features of the disease by a systematic review of previously published cases. Overall, 58 cases (22 female, 36 male; median age 10 years, range: 2-17 years), derived from 38 reports, were reviewed. Forty-five patients (76%) had flulike or respiratory symptoms prior to the onset of neurologic disease, and 23 patients (40%) presented with pulmonary infiltrates. Cerebrospinal fluid (CSF) pleocytosis (mostly mononuclear cells) and elevated cerebrospinal fluid protein counts were present in 34 (59%) and 21 (36%) patients, respectively. Cranial computed tomography (CT) or magnetic resonance imaging (MRI) abnormalities were seen in 18 (31%) and 17 (29%) patients, respectively, whereby various different presentations were observed. Forty-four patients (76%) received antimicrobial therapy active against mycoplasmas, most frequently erythromycin (n = 29) or minocycline (n = 6). Only in one patient, cure was directly attributed to antimicrobial therapy (with chloramphenicol) by the respective authors. Thirty-three patients (57%) recovered without sequelae, 20 patients (34%) had minor to major sequelae, and 5 patients (9%) died. A high cerebrospinal fluid cell count, cerebrospinal fluid protein elevation, and higher age were associated with an unfavorable outcome.

Influenza virus and CNS manifestations

Neurological involvement during influenza infection has been described during epidemics and is often consistent with serious sequelae or death. An increasing incidence of influenza-associated encephalitis/encephalopathy has been reported in Japan, mainly in children. A variety of other clinical CNS manifestations, such as Reye's syndrome, acute necrotising encephalopathy (ANE), and myelitis as well as autoimmune conditions, such as Guillain-Barre's syndrome, may occur during the course of influenza infection. Virological diagnosis is essential and based on virus isolation, antigen detection, RNA detection by PCR, and serological analyses. Neuroimaging with CT and MRI of the brain are of prognostic value. The pathogenic mechanisms behind the influenza CNS complications are unknown. The treatment is symptomatic, with control of vital functions in the intensive care unit, antiepileptic medication and treatment against brain oedema.