Update on neuroimaging in infectious central nervous system disease

Novel Perspectives Focused on the Relationship Between Herpesvirus Encephalitis and Anti-GFAP-Antibody-Positive Astrocytopathy

Virus encephalitis (VE), recognized as one of the common kinds of central nervous system (CNS) diseases after virus infection, has a surprising correlation with autoimmune encephalitis (AE) when autoimmune antibodies emerge in cerebrospinal fluid (CSF) or serum. Herpes simplex virus and Epstein-Barr virus are the most critical agents worldwide. By molecular mimicry, herpes viruses can invade the brain directly or indirectly. As a type-III intermediate filament, glial fibrillary acidic protein (GFAP) can be seen in both the central and peripheral nervous system and is regarded as a marker of astrocyte activation. Autoimmune glial fibrillary acidic protein astrocytopathy (GFAP-A), an autoimmune inflammatory CNS disorder with unearthed pathogenic mechanism yet, is correlated with CD8 + T cells and AQP4 astrocytopathy in TNF signaling. It brings a new concept of VE and GFAP coexisting, which has been documented in several case reports. Considering the infectious role of herpes viruses in CNS, EBV contributes to GFAP-IgG significantly and may result in GFAP-A. Coincidently, the existence of GFAP-IgG in patients with infection of herpes viruses has been documented as well. There exist multiple diagnoses of VE, ranging from traditional diagnostic criteria, such as CSF examination and electronic techniques, to a novel approach, according to case reports, the detection of GFAP-lgG. In terms of treatment, except for (IVIG), the explorations for new curative targets and optimal diagnostic time are of great necessity. In conclusion, emphasis given to the CNS autoimmune effect brought by the virus infection is highly worthy.

Plasma-Derived Neuronal Exosomal CircRNAs as Potential Biomarkers for Central Nervous System Infections

Infections of central nervous system (ICNSs) are inflammatory diseases caused by infectious agents that can infiltrate the brain and spinal cord through various routes, including the bloodstream, peripheral nerves, or cranial nerves. Exosomes are found in plasma and have the capacity to cross the blood-brain barrier (BBB). Exosome constituents, including lipids, proteins, DNA, and RNA, change significantly over time and are correlated with the course of disease. Circular RNA (circRNA) has become a potential biomarker for various diseases, such as ICNSs. This study explores the diagnostic potential of circRNAs derived from brain-derived exosomes in ICNSs. Our research shows that the brain-derived exosomes from patients with CNS illnesses have different patterns of circRNA expression than those from healthy controls. Plasma samples from patients with bacterial ICNSs show significantly elevated levels of hsa_circ__0020840 and hsa_circ_0116108. In contrast, higher expression levels of hsa_circ_0056947 and hsa_circ_0021531 are observed in plasma samples from individuals with viral ICNSs compared to healthy subjects. These observations suggest their potential utility as sensitive and specific biomarkers for these diseases. Moreover, the capacity of circRNAs to be encapsulated within exosomes and released into circulation offers a noninvasive approach for diagnosing ICNSs. These findings highlight the promise of utilizing brain-derived exosomal circRNAs as novel diagnostic markers for ICNSs, which may have implications for improving patient outcomes and disease management.

A systematic review of brain imaging findings in neurological infection with Japanese encephalitis virus compared with Dengue virus

OBJECTIVES

Japanese encephalitis virus (JEV) and dengue virus (DENV) represent important causes of encephalitis in Asia. Brain imaging may provide diagnostic clues about the etiology of infectious encephalitis. We performed a systematic review of brain imaging findings in Japanese encephalitis (JE) and DENV neurological infection (dengue) to identify characteristic lesions.

METHODOLOGY

Five databases were searched. We included all study types and imaging techniques. Laboratory methods were categorized using diagnostic confidence levels. Imaging data were synthesized, and focal findings are presented as proportions for JE and dengue and for subgroups based on diagnostic confidence.

PRINCIPAL FINDINGS

Thalamic lesions were the most reported magnetic resonance imaging finding in both diseases but appeared to occur more often in JE (74% in 23 studies) than dengue (29.4% in 58 studies). In cases diagnosed with antigen or nucleic acid tests, thalamic lesions were reported frequently in both JE (76.5% in 17 studies) and dengue (65.2% in 23 studies).

SIGNIFICANCE

The results suggest that thalamic lesions frequently occur in both JE and dengue encephalitis. No radiological findings were found to be pathognomonic of either disease. Although brain imaging may support a diagnosis, laboratory confirmation with highly specific tests remains crucial.

Infectious Meningitis and Encephalitis

Infectious meningitis and encephalitis are associated with significant morbidity and mortality worldwide. Acute bacterial meningitis is rapidly fatal and early recognition and institution of therapy are imperative. Viral meningitis is typically a benign self-limited illness. Chronic meningitis (defined as presenting with >4 weeks of symptoms) is most often caused by tuberculosis and fungal infection. Because the diagnostic testing for tuberculous meningitis is insensitive and cultures often take weeks to grow, therapy is often initiated empirically when the diagnosis is suspected. Human simplex virus encephalitis is the most common cause of encephalitis and requires prompt treatment with intravenous acyclovir.

Efficient control of Japanese encephalitis virus in the central nervous system of infected pigs occurs in the absence of a pronounced inflammatory immune response

Background

Japanese encephalitis virus (JEV) is the leading cause of viral encephalitis in Asia. JEV infection of mice and humans can lead to an uncontrolled inflammatory response in the central nervous system (CNS), resulting in a detrimental outcome. Pigs act as important amplification and reservoir hosts, and JEV infection of pigs is mostly subclinical. Information on virus spread in the CNS and immune responses controlling JEV infection in the CNS of pigs, however remains scarce.

Methods

Nine-week-old pigs were inoculated intranasal or intradermal with a relevant dose of 10⁵ TCID₅₀ of JEV genotype 3 Nakayama strain. Clinical signs were assessed daily, and viral spread was followed by RT-qPCR. mRNA expression profiles were determined to study immune responses in the CNS.

Results

Besides a delay of 2 days to reach the peak viremia upon intranasal compared to intradermal inoculation, the overall virus spread via both inoculation routes was highly similar. JEV appearance in lymphoid and visceral organs was in line with a blood-borne JEV dissemination. JEV showed a particular tropism to the CNS but without the induction of neurological signs. JEV entry in the CNS probably occurred via different hematogenous and neuronal pathways, but replication in the brain was mostly efficiently suppressed and associated with a type I IFN-independent activation of OAS1 expression. In the olfactory bulb and thalamus, where JEV replication was not completely controlled by this mechanism, a short but strong induction of chemokine gene expression was detected. An increased IFNy expression was simultaneously observed, probably originating from infiltrating T cells, correlating with a fast suppression of JEV replication. The chemokine response was however not associated with the induction of a strong inflammatory response, nor was an induction of the NLRP3 inflammasome observed.

Conclusions

These findings indicate that an adequate antiviral response and an attenuated inflammatory response contribute to a favorable outcome of JEV infection in pigs and help to explain the limited neurological disease compared to other hosts. We show that the NLRP3 inflammasome, a key mediator of neurologic disease in mice, is not upregulated in pigs, further supporting its important role in JEV infections.

A 9-month retrospective evaluation of the aetiology and management of patients presenting with encephalitis/meningoencephalitis at a South London hospital

Encephalitis causes high morbidity and mortality. An incidence of 4.3 cases of encephalitis/100 000 population has been reported in the UK. We performed a retrospective evaluation of the diagnosis and management of adults admitted to hospital with a clinical diagnosis of encephalitis/meningoencephalitis. Clinical, laboratory and radiological data were collated from electronic records. Thirty-six patients, median age 55 years and 24 (67%) male were included. The aetiology was confirmed over nine months in 25 (69%) of whom 16 were infections (six viral, seven bacterial, two parasitic and one viral and parasitic co-infection); 7 autoimmune; 1 metabolic and 1 neoplastic. Of 24 patients with fever, 15 (63%) had an infection. The median time to computed topography, magnetic resonance imaging and electroencephalography (EEG) was 1, 8 and 3 days respectively. Neuroimaging was abnormal in 25 (69%) and 17 (89%) had abnormal EEGs. Only 19 (53%) received aciclovir treatment. Six (17%) made good recoveries, 16 (44%) had moderate disability, 8 (22%) severe disability and 6 (17%) died. Outcomes were worse for those with an infectious cause. In summary, a diagnosis was made in 69.4% of patients admitted with encephalitis/meningoencephalitis. Autoimmune causes are important to consider at an early stage due to a successful response to treatment. Only 53% of patients received aciclovir on admission. Neuroimaging and EEG studies were delayed. The results of this work resulted in further developing the clinical algorithm for managing these patients.

Capnocytophaga bacteremia precipitating severe thrombocytopenia and preterm labor in an asplenic host

Capnocytophaga species are gram-negative bacilli that inhabit mammalian oral surfaces and can cause opportunistic infection, especially in asplenic patients. The species Capnocytophaga canimorsus is particularly associated with dog bites and is known to cause endocarditis, meningitis, and sepsis in the general population. In pregnant patients, infections tied to Capnocytophaga species from human flora have been associated with preterm labor, chorioamnionitis, and neonatal septicemia. There is little known about the effects of zoonotically-acquired Capnocytophaga infection in pregnant patients. In this case report, we present a patient with Capnocytophaga bacteremia acquired after a dog bite associated with profound thrombocytopenia and preterm labor. Dog bites are common in the United States, and we present basic recommendations for management of dog bites in pregnant patients in order to avoid morbidity associated with delay in time to antibiotic treatment of infection as described in this case.

Japanese Encephalitis Vaccine: Recommendations of the Advisory Committee on Immunization Practices

This report updates the 2010 recommendations from the CDC Advisory Committee on Immunization Practices (ACIP) regarding prevention of Japanese encephalitis (JE) among U.S. travelers and laboratory workers (Fischer M, Lindsey N, Staples JE, Hills S. Japanese encephalitis vaccines: recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Recomm Rep 2010;59[No. RR-1]). The report summarizes the epidemiology of JE, describes the JE vaccine that is licensed and available in the United States, and provides recommendations for its use among travelers and laboratory workers.JE virus, a mosquitoborne flavivirus, is the most common vaccine-preventable cause of encephalitis in Asia. JE occurs throughout most of Asia and parts of the western Pacific. Approximately 20%-30% of patients die, and 30%-50% of survivors have neurologic, cognitive, or behavioral sequelae. No antiviral treatment is available.Inactivated Vero cell culture-derived JE vaccine (Ixiaro [JE-VC]) is the only JE vaccine that is licensed and available in the United States. In 2009, the U.S. Food and Drug Administration (FDA) licensed JE-VC for use in persons aged ≥17 years; in 2013, licensure was extended to include children aged ≥2 months.Most travelers to countries where the disease is endemic are at very low risk for JE. However, some travelers are at increased risk for infection on the basis of their travel plans. Factors that increase the risk for JE virus exposure include 1) traveling for a longer period; 2) travel during the JE virus transmission season; 3) spending time in rural areas; 4) participating in extensive outdoor activities; and 5) staying in accommodations without air conditioning, screens, or bed nets. All travelers to countries where JE is endemic should be advised to take precautions to avoid mosquito bites to reduce the risk for JE and other vectorborne diseases. For some persons who might be at increased risk for JE, the vaccine can further reduce the risk for infection. The decision about whether to vaccinate should be individualized and consider the 1) risks related to the specific travel itinerary, 2) likelihood of future travel to countries where JE is endemic, 3) high morbidity and mortality of JE, 4) availability of an effective vaccine, 5) possibility (but low probability) of serious adverse events after vaccination, and 6) the traveler's personal perception and tolerance of risk.JE vaccine is recommended for persons moving to a JE-endemic country to take up residence, longer-term (e.g., ≥1 month) travelers to JE-endemic areas, and frequent travelers to JE-endemic areas. JE vaccine also should be considered for shorter-term (e.g., <1 month) travelers with an increased risk for JE on the basis of planned travel duration, season, location, activities, and accommodations and for travelers to JE-endemic areas who are uncertain about their specific travel duration, destinations, or activities. JE vaccine is not recommended for travelers with very low-risk itineraries, such as shorter-term travel limited to urban areas or outside of a well-defined JE virus transmission season.

Emergency Department Approach to the Patient with Suspected Central Nervous System Infection

Central nervous system (CNS) infections require early recognition and aggressive management to improve patient survival and prevent long-term neurologic sequelae. Although early detection and treatment are important in many infectious syndromes, CNS infections pose unique diagnostic and therapeutic challenges. The nonspecific signs and symptoms at presentation, lack of characteristic infectious changes in laboratory and imaging diagnostics, and closed anatomic and immunologically sequestered space each present challenges to the emergency physician. This article proposes an approach to the clinical evaluation of patients with suspected CNS infection and highlights methods of diagnosis, treatment, and complications associated with CNS infections.

A Different Perspective on the Phenomenon of Hemiplegic Encephalitis: A Case Report

Encephalitis is an acute inflammation of the central nervous system that is characterized by fever, headache, and sleep disorders. Among the causes of meningoencephalitis are bacterial and viral infections, autoimmune diseases, and drug reactions. This case report describes a male patient who experienced hemiplegia following encephalitis. A 35-year-old patient consulted a physician with complaints of fever and headache. The clinical evaluation was encephalitis and the patient was treated accordingly. A severe neurological deficit developed, and the patient became bedridden, After treatment, the patient was included in an inpatient physical therapy program and was subsequently discharged with the ability to walk using parallel bars. The aim of this case report was to draw attention to the rehabilitation process applied after the diagnosis and treatment of a patient with hemiplegia that developed as a complication of encephalitis.

Management of Viral Central Nervous System Infections: A Primer for Clinicians

Viruses are a common cause of central nervous system (CNS) infections with many host, agent, and environmental factors influencing the expression of viral diseases. Viruses can be responsible for CNS disease through a variety of mechanisms including direct infection and replication within the CNS resulting in encephalitis, infection limited to the meninges, or immune-related processes such as acute disseminated encephalomyelitis. Common pathogens including herpes simplex virus, varicella zoster, and enterovirus are responsible for the greatest number of cases in immunocompetent hosts. Other herpes viruses (eg, cytomegalovirus, John Cunningham virus) are more common in immunocompromised hosts. Arboviruses such as Japanese encephalitis virus and Zika virus are important pathogens globally, but the prevalence varies significantly by geographic region and often season. Early diagnosis from radiographic evidence and molecular (eg, rapid) diagnostics is important for targeted therapy. Antivirals may be used effectively against some pathogens, although several viruses have no effective treatment. This article provides a review of epidemiology, diagnostics, and management of common viral pathogens in CNS disease.

Toxoplasma gondii-A Gastrointestinal Pathogen Associated with Human Brain Diseases

Serious psychiatric disorders such as schizophrenia, bipolar disorder, and major depression are important causes of mortality and morbidity worldwide. While these are primarily diseases involving altered brain functioning, numerous studies have documented increased rates of gastrointestinal inflammation and dysfunction in many individuals with these disorders. Toxoplasma gondii is an apicomplexan protozoan intracellular parasite with a widespread distribution in both developed and developing countries. Toxoplasma organisms enter the ecosystem through the shedding of oocysts by Toxoplasma-infected felines. In almost all cases of postnatal human infection, Toxoplasma enters its hosts through the intestinal tract either by the ingestion of oocysts or by the consumption of meat from food animals which themselves were infected by Toxoplasma oocysts. It had previously been thought that most cases of Toxoplasma infection in immune competent children and adults were inapparent and asymptomatic. However, recent studies cast doubt on this concept as exposure to Toxoplasma has been associated with a range of acute and chronic symptoms. Of particular note has been the finding of an increased rate of a range of neurological and psychiatric disorders associated with serological evidence of Toxoplasma exposure. A role of Toxoplasma infection in brain diseases is also supported by the consistent finding of altered cognition and behavior in animal models of infections. Much of the attention relating to the role of Toxoplasma infection in neuropsychiatric disorders has focused on the brain, where Toxoplasma tissue cysts can persist for extended periods of time. However, recent discoveries relating to the role of the gastrointestinal tract in cognition and behavior suggest that Toxoplasma may also increase susceptibility to human brain diseases through immune activation, particularly involving the gastrointestinal mucosa. The study of the pathways relating to the pathobiology and immunology of Toxoplasma infection may provide insights into the pathogenesis of a range of human neuropsychiatric disorders as well as into cognitive functioning in otherwise healthy individuals.

Diagnostic value of lumbar puncture among infants and children presenting with fever and convulsions

Introduction

Central nervous system (CNS) infections can be categorized according to the nature of the infectious pathogen into viral, bacterial, protozoan, or fungal. The diagnosis of diffuse CNS infections depends on examination of cerebrospinal fluid (CSF) obtained by lumbar puncture (LP). The aim of this work was to determine the diagnostic value of CSF analysis in infants and children presenting with fever and convulsions.

Methods

Detailed clinical data of infants and children included in this study were collected with special reference to the course and duration of the illness, description of the convulsions, consciousness level, signs of increased intracranial pressure, and signs of meningeal irritation. Lumbar puncture and chemical and bacteriological analyses of the obtained cerebrospinal fluid were done for all of the children.

Results

The total number of children included in the study was 85, they had a median age 19 months, and 88% of them had generalized convulsions. CSF examination revealed that 20% had abnormal physical findings, while 23.5% had abnormal white blood cell count (WBC) (CSF Pleocytosis). CSF cultures were done in three cases with the highest White blood cells (WBCs), and streptococcus pneumoniae was present in all three cases.

Conclusion

This study found that CNS infections are not uncommon in infants and children presenting with fever and convulsions in our locality, and acute bacterial meningitis cannot be excluded. However, its presence in the absence of clinical symptoms and signs of meningeal irritation is a remote possibility, but it should always be considered.

A study on viral CNS inflammation beyond herpes encephalitis

The early diagnosis of herpes simplex virus encephalitis (HSVE) enables induction of antiviral therapy in this potentially life-threatening disease. The study aimed to determine clinical findings including cerebrospinal fluid (CSF) data and MRI imaging in HSVE patients and to identify features distinguishing HSVE from encephalitis of other viral etiologies. We retrospectively reviewed consecutive patients who were diagnosed with viral encephalitis between 2000 and 2014 at the University Hospital Halle. Forty-nine patients with viral encephalitis were identified. A viral etiology could be confirmed by PCR or antibody testing in 22/49 (44.9 %) of patients (15 (30.6 %) HSV, 5 (10.2 %) VZV, 2 (4.1 %) EBV). In HSVE, typical findings were focal slowing in electroencephalophy (EEG) (80 %, p = 0.021) and presence of cortical (86.7 %, p = 0.030) lesions in MRI. Restricted diffusion was particularly helpful in detection of early signal abnormalities in HSVE (p = 0.014). In 27/49 (55.1 %) of patients, no causative agent could be elucidated. In these patients, 15/27 (55.6 %) experienced a rather "benign" disease course with no MRI pathology despite initially HSVE mimicking clinical picture. However, CSF was significantly different showing a higher amount of granulocytes and activated lymphocytes. The remaining 12/27 (44.4 %) patients developed MRI changes consistent with encephalitis, in 4 of these patients, disease course was fatal. Beside PCR-based serology as standard procedure, MRI including diffusion-weighted images and EEG represent additional tools in early HSVE diagnosis. CSF cytology might be particularly supportive in differentiating likely benign forms of encephalitis.

Imaging in Neurologic Infections II: Fungal and Viral Diseases

Infections of the nervous system have a significant impact on global mortality and morbidity. These infections are medical emergencies that are frequently diagnostically challenging. Incorporation of neuroimaging can be essential for early diagnosis and initiation of proper treatment. In this second part of this two-part review, we focus on diagnostic imaging features of selected fungal and viral nervous system infections.

Unusual Larva in the CSF and Unique MRI Findings in a Case of Eosinophilic Meningitis

Eosinophilic meningitis may be caused by non-infectious and infectious agents. Angiostrongylus cantonensis is the commonest causative agent of eosinophilic meningitis. Rats are the primary hosts of this parasite. Humans get infected by ingestion of raw or inadequately cooked hosts (snails or monitor lizard) or food contaminated with the infective third-stage larvae. A 16-year-old boy was admitted to our hospital with history of fever, headache, and altered sensorium. Magnetic resonance imaging of the brain showed unique findings. Cerebrospinal fluid (CSF) examination showed eosinophilia and the CSF wet mount identified a larva. Patient history revealed ingestion of monitor lizard 2 weeks prior to onset of symptoms. Hence, a diagnosis of eosinophilic meningitis caused by A. cantonensis was made. He was treated with oral albendazole and steroids, resulting in gradual improvement. A. cantonensis as a cause of eosinophilic meningitis is a possibility in patients who present with headache and vomiting after eating raw meat (monitor lizard). To the best of our knowledge, this is a very rare case being reported from India where the larva was identified during the microscopic examination of the CSF.

ACR Appropriateness Criteria Headache

Most patients presenting with uncomplicated, nontraumatic, primary headache do not require imaging. When history, physical, or neurologic examination elicits "red flags" or critical features of the headache, then further investigation with imaging may be warranted to exclude a secondary cause. Imaging procedures may be diagnostically useful for patients with headaches that are: associated with trauma; new, worse, or abrupt onset; thunderclap; radiating to the neck; due to trigeminal autonomic cephalgia; persistent and positional; and temporal in older individuals. Pregnant patients, immunocompromised individuals, cancer patients, and patients with papilledema or systemic illnesses, including hypercoagulable disorders may benefit from imaging. Unlike most headaches, those associated with cough, exertion, or sexual activity usually require neuroimaging with MRI of the brain with and without contrast to exclude potentially underlying pathology before a primary headache syndrome is diagnosed. The ACR Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed every 2 years by a multidisciplinary expert panel. The guideline development and review include an extensive analysis of current medical literature from peer-reviewed journals and the application of a well-established consensus methodology (modified Delphi) to rate the appropriateness of imaging and treatment procedures by the panel. In those instances in which evidence is lacking or not definitive, expert opinion may be used to recommend imaging or treatment.

Biomarkers in Japanese encephalitis: a review

JE is a flavivirus generated dreadful CNS disease which causes high mortality in various pediatric groups. JE disease is currently diagnosed by measuring the level of viral antigens and virus neutralization IgM antibodies in blood serum and CSF by ELISA. However, it is not possible to measure various disease-identifying molecules, structural and molecular changes occurred in tissues, and cells by using such routine methods. However, few important biomarkers such as cerebrospinal fluid, plasma, neuro-imaging, brain mapping, immunotyping, expression of nonstructural viral proteins, systematic mRNA profiling, DNA and protein microarrays, active caspase-3 activity, reactive oxygen species and reactive nitrogen species, levels of stress-associated signaling molecules, and proinflammatory cytokines could be used to confirm the disease at an earlier stage. These biomarkers may also help to diagnose mutant based environment specific alterations in JEV genotypes causing high pathogenesis and have immense future applications in diagnostics. There is an utmost need for the development of new more authentic, appropriate, and reliable physiological, immunological, biochemical, biophysical, molecular, and therapeutic biomarkers to confirm the disease well in time to start the clinical aid to the patients. Hence, the present review aims to discuss new emerging biomarkers that could facilitate more authentic and fast diagnosis of JE disease and its related disorders in the future.

An update on diagnostic imaging studies for viral encephalitis

Viral encephalitis is still a life-threatening disease occurring at any age. It is critical to make a rapid and correct diagnosis for a better outcome of the disease. Accumulating evidence has suggested that MRI is a powerful tool for the detection of any lesion of the CNS caused by viral infections and helps to initiate the timely treatment. In this review, we summarize the current understanding of MRI findings of viral encephalitis, especially related to HSV, HIV, varicella zoster, Japanese encephalitis, John Cunningham, and influenza viruses. With these considerations, we learnt that the inclusion of diffusion-weighted image sequences on routine MRI examination would have a significant value in detecting the pathologic changes that occur following viral invasion of the CNS.

Imaging of central nervous system viral diseases

Viral infections of the central nervous system (CNS) are commonly encountered and there has been continued emergence of new neurotropic viruses which are being frequently recognized. These may present clinically as encephalitis, meningitis, encephalomyelitis, and encephalomyeloradiculitis. The clinical manifestations are usually nonspecific and diagnosis is usually based on the laboratory investigations. Imaging plays a role in its early detection and at times suggests the specific diagnosis that may help in early institution of appropriate therapy. In this review, we summarize the pathology, clinical, and imaging features of the common viral infections that affect the CNS.

Neuro-intensive care of patients with acute CNS infections

Infections in the central nervous system (CNS) are caused by a wide range of microorganisms resulting in distinct clinical syndromes including meningitis, encephalitis, and pyogenic infections, such as empyema and brain abscess. Bacterial and viral infections in the CNS can be rapidly fatal and can result in severe disability in survivors. Appropriate identification and acute management of these infections often occurs in a critical care setting and is vital to improving outcomes in this group of patients. This review of diagnosis and management of acute bacterial and viral infections in the CNS provides a general approach to patients with a suspected CNS infection and also provides a more detailed review of the diagnosis and management of patients with suspected bacterial meningitis, viral encephalitis, brain abscess, and subdural empyema.

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.

Pathology of tropical diseases

Tropical diseases affecting the central nervous system include infections, infestations, and nutritional deficiency disorders. This article discusses the commonly encountered diseases. The infections include bacterial, mycobacterial, fungal, parasitic, and viral infections with varied clinical manifestations. Imaging sensitivity and specificity for the prediction of the cause of infections has improved with application of advanced techniques. Microbial demonstration and histology remain the gold standard for diagnosis. Understanding the basis of imaging changes is mandatory for better evaluation of images. Nutritional disorders present with generalized and nonspecific imaging manifestations. The pathology of commonly encountered vitamin deficiencies is also discussed.

Diffusion MR imaging for monitoring treatment response

The objective of this article was to emphasize the use of diffusion-weighted imaging in the diagnosis and follow-up of several major disease contexts, as established in recent literature. In some of these diseases the diffusion changes are correlated with the clinical deficit and are potentially useful for early diagnosis and longitudinal evaluation, as well as in the context of pharmacologic trials. Diffusion magnetic resonance is a major advance in the continuing evolution of MR imaging. It provides contrasts and characterization between tissues at a cellular level that may imply differences in function as well as framework and have contributed to a better understanding of the pathophysiological mechanisms of several diseases.

Leukoencephalopathy in pneumococcal meningitis: a diagnostic pitfall and treatment challenge

We present a case of pneumococcal meningitis complicated by leukoencephalopathy. Possible pathogenic mechanisms, a diagnostic pitfall, and optimal treatment options are discussed.

Emergent neuroimaging of intracranial infection/inflammation

Infectious and inflammatory processes of the intracranial compartment often result in acute clinical presentations. The possible causes are legion. Clues to the diagnosis involve clinical presentation, laboratory analysis, and neuroimaging. This article reviews some of the salient factors in understanding intracranial infection/ inflammation, including pathophysiology and neuroimaging protocols/findings, and provides some examples and a few "pearls and pitfalls."

Viral infections of the central nervous system: a case-based review

Three patients with viral infections of the central nervous system (CNS) were evaluated on an inpatient infectious diseases consultation service within a two-week period. These cases, caused by herpes simplex virus, varicella zoster virus and enterovirus, highlight the importance of viral pathogens in causing debilitating infections of the CNS and provide examples of the utility of molecular diagnostics in evaluating patients with encephalitis and meningitis. The importance of antiviral therapy is particularly underscored by these cases, as is the variability in response of patients to such agents.

Clinically presenting acute/subacute ischemic stroke: differential diagnosis of the non-enhanced CT hypodensity by advanced neuroimaging

OBJECTIVES

Patients presenting to the emergency room with an acute or subacute onset of focal neurological deficits are evaluated initially by non-contrast computed tomogram (CT) of the brain. This is primarily carried out to differentiate an ischemic from hemorrhagic stroke. However, other neurological conditions may have a similar clinical presentation as well as only hypodensities on CT scan, thus mimicking ischemic stroke. This review focuses on the advanced neuroimaging modalities that help differentiate these other conditions from a cerebral infarction.

METHODS

The literature was reviewed in order to ascertain what conditions would clinically and by CT mimic an acute/subacute ischemic infarction, and what advanced neuroimaging techniques would be most useful in differentiating these conditions.

RESULTS

Several infectious, inflammatory, metabolic and vascular diseases were found with clinical presentations identical to subacute/acute ischemic cerebral infarction, which also could demonstrate only hypodensities on a non-enhanced CT scan. However, advanced neuroimaging techniques could readily differentiate these conditions from ischemic infarction.

CONCLUSIONS

As presented in this review, although several diseases initially present a diagnostic dilemma upon presentation because of their clinical and non-enhanced CT similarities to cerebral infarction, advanced diagnostic neuroimaging readily establishes their unique pathologies.

Early cortical cytotoxic edema in meningococcal meningitis

Meningococcal disease frequently presents neurologic sequels via vascular, metabolic, or inflammatory processes. Understanding the underlying pathogenic mechanisms may influence both treatment and outcome. We present a 2-year-old child affected by Neisseria meningitidis sepsis, who on the second day from clinical onset manifested recurrent partial motor seizures and focal neurologic signs. An early magnetic resonance angiography of the circle of Willis produced normal results, whereas magnetic resonance imaging of the brain disclosed cortical signal abnormalities consistent with cytotoxic edema, without involvement of the adjacent white matter. Six-month follow-up magnetic resonance imaging of the brain indicated faint cortical atrophy in the same regions, although the neurologic picture had resolved. The literature contains few data on early magnetic resonance parenchymal changes, and their pathogenic mechanism is controversial. Diffusion-weighted images may contribute to an understanding of the mechanisms of such brain damage.

Central nervous system infections

Central nervous system infections have long been recognized as among the most devastating of diseases. This article describes the changing pattern and epidemiology of a variety of common central nervous system infections, including meningitis, encephalitis, and brain abscesses, and reviews pathophysiology and the most current approach to clinical diagnosis, treatment, and disposition from the emergency physician perspective.

Unravelling the pathophysiology of delirium: a focus on the role of aberrant stress responses

Delirium is a common and serious acute neuropsychiatric syndrome with core features of inattention and cognitive impairment, and associated features including changes in arousal, altered sleep-wake cycle, and other changes in mental status. The main risk factors are old age, cognitive impairment, and other comorbidities. Though delirium has consistent core clinical features, it has a very wide range of precipitating factors, including acute illness, surgery, trauma, and drugs. The molecular mechanisms by which these precipitating factors lead to delirium are largely obscure. In this article, we attempt to narrow down some specific causal pathways. We propose a basic classification for the etiological factors: (a) direct brain insults and (b) aberrant stress responses. Direct brain insults are largely indiscriminate and include general and regional energy deprivation (e.g., hypoxia, hypoglycaemia, stroke), metabolic abnormalities (e.g., hyponatraemia, hypercalcaemia), and the effects of drugs. Aberrant stress responses are conceptually and mechanistically distinct in that they constitute adverse effects of stress-response pathways, which, in health, are adaptive. Ageing and central nervous system disease, two major predisposing factors for delirium, are associated with alterations in the magnitude or duration of stress and sickness behavior responses and increased vulnerability to the effects of these responses. We discuss in detail two stress response systems that are likely to be involved in the pathophysiology of delirium: inflammation and the sickness behavior response, and activity of the limbic-hypothalamic-pituitary-adrenal axis. We conclude by discussing the implications for future research and the development of new therapies for delirium.

The management of encephalitis: clinical practice guidelines by the Infectious Diseases Society of America

Guidelines for the diagnosis and treatment of patients with encephalitis were prepared by an Expert Panel of the Infectious Diseases Society of America. The guidelines are intended for use by health care providers who care for patients with encephalitis. The guideline includes data on the epidemiology, clinical features, diagnosis, and treatment of many viral, bacterial, fungal, protozoal, and helminthic etiologies of encephalitis and provides information on when specific etiologic agents should be considered in individual patients with encephalitis.

Central nervous system infections of herpesvirus family

Herpesviruses are one of the most common groups of pathogens causing central nervous system infections in humans. They mostly cause encephalitis, meningitis, or myelitis in immunocompetent and immunocompromised patients. Children, adults, and the elderly can all be affected. Although contrast-enhanced CT is more widely used for diagnosis, contrast-enhanced MR imaging combined with diffusion-weighted imaging is superior to CT in the detection of early changes and the real extent of the disease, and in assessing prognosis and monitoring response to antiviral treatment. More sophisticated techniques, such as MR spectroscopy and perfusion imaging, can aid in the differential diagnosis of herpesvirus infections from other tumoral, demyelinating, and ischemic processes.

The spectrum of herpes simplex encephalitis in children

Clinical and basic science research carried out in recent years into herpes simplex encephalitis (HSE) have shown that the concept of a "classical" picture of HSE in children is now outdated and that our current knowledge of the disease is probably only the tip of an iceberg. Indeed, increasing evidence supports the existence of a wider range of pathophysiological mechanisms, clinical presentations and disease progressions in paediatric HSE. This paper reviews the clinical, biological and radiological data available and redefines the spectrum of HSE in children. Full understanding of the condition should improve the management of suspected cases and decrease the morbidity and the mortality associated with this disease.

Early diffusion-weighted magnetic resonance imaging findings in neonatal herpes encephalitis

Neonatal herpes encephalitis is usually caused by herpes simplex virus type 2 and results in significant morbidity and mortality. Imaging diagnosis with ultrasound, computed tomography scan and conventional magnetic resonance imaging may be normal in the early course of the disease. In this case diffusion-weighted magnetic resonance imaging detected the disease process earlier and better than the conventional T2-weighted or fluid-attenuated inversion recovery imaging sequences. The use of diffusion-weighted magnetic resonance imaging in neonatal herpes encephalitis proved to be a useful tool in the early stage of the disease.