Fungal brain abscess in transplant recipients: epidemiologic, microbiologic, and clinical features

Brain abscess following kidney transplantation: A single centre observational study from North India

Background

Amongst the infections in kidney transplant recipients, brain abscess represents an uncommon life-threatening complication. Mortality continues to be high despite improvements in diagnostics and therapeutics.

Method

We conducted an observational study, describing the incidence, presentation, implicating pathogen, management and outcome of brain abscess following kidney transplantation at our centre.

Result

Amongst the 1492 patients who underwent kidney transplantation at our centre between June 1991 and January 2023 (cumulative follow-up: 4936 patient-years), five females and four males, developed brain abscesses. The incidence proportion (risk) is 0.6% with an incidence rate of 6.03 cases per 1000 patient years. The median duration from transplant to development of brain abscess was 5 weeks (range: 4 weeks to 9 years). The commonest presentation was a headache. A definitive microbiological diagnosis was established in eight out of nine patients. The commonest implicated organism was a dematiaceous fungus, Cladophialophora bantiana (3 patients, 33.3%). Despite the reduction in immunosuppression, surgical evacuation and optimal medical therapy, five (55.55%) patients succumbed to their illness.

Conclusions

Brain abscesses following kidney transplantation is an uncommon, life-threatening condition. It usually occurs in the early post-transplant period and the presentation is often subtle. Unlike immunocompetent individuals, a fungus is the most common causative organism in those with solid organ transplants. The management includes a reduction in immunosuppression, early antimicrobial therapy, and surgical decompression.

Intracerebral opportunistic infections caused by immunosuppressants after orthotopic liver transplantation: Report of two cases and literature review

Central nervous system (CNS) infections in adults are rare because of normal immunity and the existence of the blood brain barrier, which prevents the invasion of pathogenic microorganisms. Liver transplant recipients are at an increased risk of opportunistic infections (OI) due to immunosuppressive therapy compared to those with normal immunity. Early diagnosis and timely implementation of treatment are critical for the successful treatment of these infections. We present two cases of intracerebral OI after orthotopic liver transplantation (OLT), with different clinical presentations. Patient 1 presented with epileptic seizures, mainly manifested as unresponsiveness, unconsciousness, and coma complicated with involuntary limb twitching. Patient 2 presented with a consciousness disorder, mainly manifested as unclear consciousness content, poor orientation, calculation power, and logical ability. Next-generation sequencing (NGS) examination of the cerebrospinal fluid confirmed human herpesvirus 6 B (HHV-6B) infection in patient 1 and intracranial Aspergillus infection in patient 2. Intracranial OI has insidious onset and atypical clinical manifestations. NGS can allow for the proper diagnosis and monitoring of the effects of treatment.

Neuroimmune Responses in a New Experimental Animal Model of Cerebral Aspergillosis

Exposure of immunosuppressed individuals to the opportunistic fungal pathogen Aspergillus fumigatus may result in invasive pulmonary aspergillosis (IPA), which can lead to the development of cerebral aspergillosis (CA), a highly lethal infection localized in the central nervous system (CNS). There are no experimental models of CA that effectively mimic human disease, resulting in a considerable knowledge gap regarding mechanisms of neurological pathogenicity and neuroimmune responses during infection. In this report, immunosuppressed mice (via acute, high-dose corticosteroid administration) challenged with A. fumigatus resting conidia intranasally, followed a day later by a 70-fold lower inoculum of pre-swollen conidia intravenously (IN + IV + steroid), demonstrated increased weight loss, signs of severe clinical disease, increased fungal burden in the brain, and significant reduction in survival compared to immunosuppressed mice challenged intranasally only (IN + steroid) or non-immunosuppressed mice challenged both intranasally and intravenously (IN + IV). The IN + IV + steroid group demonstrated significant decreases in monocytes, eosinophils, dendritic cells (DCs), and invasive natural killer T (iNKT) cells, but not neutrophils or γδ T cells, in the brain compared to the IN + IV group. Likewise, the IN + IV + steroid group had significantly lower levels of interleukin (IL)-1β, IL-6, IL-17A, CC motif chemokine ligand 3 (CCL3), CXC chemokine ligand 10 (CXCL10), and vascular endothelial growth factor (VEGF) in the brain compared to the IN + IV group. IN + IV + steroid was superior to both IN + IV + chemotherapy (cytarabine + daunorubicin) and IN + IV + neutropenia for the development of CA. In conclusion, we have developed a well-defined, physiologically relevant model of disseminated CA in corticosteroid-induced immunosuppressed mice with a primary pulmonary infection. This model will serve to advance understanding of disease mechanisms, identify immunopathogenic processes, and help define the protective neuroinflammatory response to CA. IMPORTANCE Invasive fungal infections (IFIs) result in significant mortality in immunosuppressed individuals. Of these, invasive pulmonary aspergillosis (IPA), caused by the opportunistic mold Aspergillus fumigatus, is the most lethal. Lethality in IPA is due to two main factors: destruction of the lung leading to compromised pulmonary function, and dissemination of the organism to extrapulmonary organs. Of these, the CNS is the most common site of dissemination. However, very little is known regarding the pathogenesis of or immune response during cerebral aspergillosis, which is directly due to the lack of an animal model that incorporates immunosuppression, lung infection, and consistent dissemination to the CNS/brain. In this report, we have developed a new experimental animal model of CA which includes the above parameters and characterized the neuroimmune response. We further compared this disseminated CA model to two additional immunosuppressive strategies. Overall, this model of disseminated CA following IPA in an immunosuppressed host provides a novel platform for studying the efficacy of antifungal drugs and immunotherapies for improving disease outcomes.

Cerebral aspergillosis in the era of new antifungals: The CEREALS national cohort study Nationwide CEREbral Aspergillosis Lesional study (CEREALS)

BACKGROUND

Cerebral aspergillosis (CA) is a life-threatening disease for which diagnosis and management remain challenging. Detailed analyses from large cohorts are lacking.

METHODS

We included 119 cases of proven (n = 54) or probable (n = 65) CA diagnosed between 2006 and 2018 at 20 French hospitals. Data were collected at baseline and during follow-up. Cerebral imaging was reviewed centrally by two neuroradiologists.

RESULTS

The most frequent underlying conditions were hematological malignancy (40%) and solid organ transplantation (29%). Galactomannan was detected in the serum of 64% of patients. In 75% of cases, at least one of galactomannan, Aspergillus PCR, and β-d-glucan was positive in the cerebrospinal fluid. Six-week mortality was 45%. Two distinct patterns of disease were identified according to presumed route of dissemination. Presumed haematogenous dissemination (n = 88) was associated with a higher frequency of impaired consciousness (64%), shorter time to diagnosis, the presence of multiple abscesses (70%), microangiopathy (52%), detection of serum galactomannan (69%) and Aspergillus PCR (68%), and higher six-week mortality (54%). By contrast, contiguous dissemination from the paranasal sinuses (n = 31) was associated with a higher frequency of cranial nerve palsy (65%), evidence of meningitis on cerebral imaging (83%), macrovascular lesions (61%), delayed diagnosis, and lower six-week mortality (30%). In multivariate analysis and in a risk prediction model, haematogenous dissemination, hematological malignancy and the detection of serum galactomannan were associated with higher six-week mortality.

CONCLUSION

Distinguishing between hematogenous and contiguous dissemination patterns appears to be critical in the workup for CA, as they are associated with significant differences in clinical presentation and outcome.

Sticks and bones: Traumatic phaeohyphomycosis presenting as an epidural scalp abscess and cranial osteomyelitis

The pigmented molds can cause soft tissue and invasive disease (phaeohyphomycosis) in immunocompetent patients. We describe a 76-year-old male patient who developed a Cladophialophora bantiatum posterior scalp abscess and cranial osteomyelitis following an incidental scalp exposure with a tree branch. Management requires extensive surgical debridement followed by prolonged antifungal therapy.

Fungal infections of the central nervous system and paranasal sinuses in onco-haematologic patients. Epidemiological study reporting the diagnostic-therapeutic approach and outcome in 89 cases

Invasive fungal infections (IFI) of the Central Nervous System (IFI-CNS) and Paranasal Sinuses (IFI-PS) are rare, life-threatening infections in haematologic patients, and their management remains a challenge despite the availability of new diagnostic techniques and novel antifungal agents. In addition, analyses of large cohorts of patients focusing on these rare IFI are still lacking. Between January 2010 and December 2016, 89 consecutive cases of Proven (53) or Probable (36) IFI-CNS (71/89) and IFI-PS (18/89) were collected in 34 haematological centres. The median age was 40 years (range 5-79); acute leukaemia was the most common underlying disease (69%) and 29% of cases received a previous allogeneic stem cell transplant. Aspergillus spp. were the most common pathogens (69%), followed by mucormycetes (22%), Cryptococcus spp. (4%) and Fusarium spp. (2%). The lung was the primary focus of fungal infection (48% of cases). The nervous system biopsy was performed in 10% of IFI-CNS, and a sinus biopsy was performed in 56% of IFI-PS (P = 0.03). The Galactomannan test on cerebrospinal fluid has been performed in 42% of IFI-CNS (30/71), and it was positive in 67%. Eighty-four pts received a first-line antifungal therapy with Amphotericine B in 58% of cases, Voriconazole in 31% and both in 11%. Moreover, 58% of patients received 2 or more lines of therapy and 38% were treated with a combination of 2 or more antifungal drugs. The median duration of antifungal therapy was 60 days (range 5-835). A surgical intervention was performed in 26% of cases but only 10% of IFI-CNS underwent neurosurgical intervention. The overall response rate to antifungal therapy (complete or partial response) was 57%, and 1-year overall survival was 32% without significant differences between IFI-CNS and IFI-PS. The overall mortality was 69% but the IFI attributable mortality was 33%. Mortality of IFI-CNS/PS remains high but, compared to previous historical data, it seems to be reduced probably due to the availability of newer antifungal drugs. The results arising from this large contemporary cohort of cases may allow a more effective diagnostic and therapeutic management of these very rare IFI complications in haematologic patients.

Management of brain abscesses: where are we now?

INTRODUCTION

Brain abscesses affect all age groups and are not peculiar to a particular country, race, or geographical location. It is a disease that, in the past, carried a high morbidity and mortality. With improvements in medical technology and expertise, outcomes have improved tremendously. The causative organisms vary vastly and have evolved with time. Treatment of brain abscesses is primarily with antimicrobial therapy but surgery plays a vital role in achieving better outcomes.

CONTENT

In this article, we review the literature to find out how the epidemiology of this disease has changed through the years and re-visit the basic pathological process of abscess evolution and highlight the new research in the biochemical pathways that initiate and regulate this process. We also highlight how magnetic resonance imaging and its various modalities have improved diagnostic accuracy. Finally, we discuss the pros and cons of traditional open surgery versus newer minimally invasive methods.

An updated comprehensive systematic review of Cladophialophora bantiana and analysis of epidemiology, clinical characteristics, and outcome of cerebral cases

Cladophialophora bantiana is a phaeoid fungus that only rarely has been isolated from sources other than the human brain. It has a particular tropism for the central nervous system (CNS). We have integrated and updated large-scale data related to several aspects of C. Bantiana and reviewed all the available reports on its cerebral infections, focusing on their geographical distribution, infection routes, immune status of infected individuals, type and location of infections, clinical manifestations and treatment and outcome, briefly looking over the spectrum of other disease entities associated with C. bantiana, that is, extra-cerebral and animal infections and on the environmental sources of this fungus. Among the agents of phaeohyphomycosis, a term used to describe an infection caused by a dark pigmented fungus, C. bantiana has some significant specific features. A total of 120 case reports were identified with a significantly higher percentage of healthy subjects than immune-debilitated patients (58.3% vs. 41.7%). Infections due to C. bantiana occur worldwide. The main clinical manifestations are brain abscess (97.5%), coinfection of brain tissue and meninges (14.2%) and meningitis alone (2.5%). Among immunocompetent patients, cerebral infection occurred in the absence of pulmonary lesions. The mortality rate is 65.0% regardless of the patient's immune status. The therapeutic options used include surgery or antifungals alone, and the combination of both, in most cases the fatal outcome being rapid after admission. Since the fungus is a true pathogen, laboratory workers should be made aware that BioSafety Level-3 precautions might be necessary.

Central nervous system complications after allogeneic hematopoietic stem cell transplantation

Allogenic hematopoietic stem cell transplant (alloSCT) is a potentially curative modality of treatment for patients with hematological malignancies. However, CNS complications following transplant pose a risk to survival of the patients. Early recognition and management of these complications are crucial to reduce morbidity and mortality of patients following transplant. Early CNS complications associated with alloSCT are infection, cerebrovascular events, chemotherapy and radiation-induced toxicities while late complications include post-transplant lymphoproliferative disorder, CNS relapse of underlying malignancy and viral and fungal infections. Development of graft-versus-host disease can further increase the risk of CNS complications and outcomes after alloSCT. Strategies aimed to reduce the risk of CNS complications and early management may ameliorate the morbidity and mortality in transplant recipients.

Genomic Analyses of Cladophialophora bantiana, a Major Cause of Cerebral Phaeohyphomycosis Provides Insight into Its Lifestyle, Virulence and Adaption in Host

Cladophialophora bantiana is a dematiaceous fungus with a predilection for causing central nervous system (CNS) infection manifesting as brain abscess in both immunocompetent and immunocompromised patients. In this paper, we report comprehensive genomic analyses of C. bantiana isolated from the brain abscess of an immunocompetent man, the first reported case in Malaysia and Southeast Asia. The identity of the fungus was determined using combined morphological analysis and multilocus phylogeny. The draft genome sequence of a neurotrophic fungus, C. bantiana UM 956 was generated using Illumina sequencing technology to dissect its genetic fundamental and basic biology. The assembled 37.1 Mb genome encodes 12,155 putative coding genes, of which, 1.01% are predicted transposable elements. Its genomic features support its saprophytic lifestyle, renowned for its versatility in decomposing hemicellulose and pectin components. The C. bantiana UM 956 was also found to carry some important putative genes that engaged in pathogenicity, iron uptake and homeostasis as well as adaptation to various stresses to enable the organism to survive in hostile microenvironment. This wealth of resource will further catalyse more downstream functional studies to provide better understanding on how this fungus can be a successful and persistent pathogen in human.

Central Nervous System Complications of Hematopoietic Stem Cell Transplant

Hematopoietic stem cell transplantation (SCT) is now commonly used to treat several hematologic and nonhematologic diseases. Central nervous system (CNS) complications post-transplantation occur commonly in the first year and result in increased mortality from infectious, toxic, metabolic, or vascular causes. Infections secondary to aspergillus, toxoplasma and viruses cause many of the complications. Drug-related toxicities arising from conditioning regimens and graft-versus-host disease prophylaxis, as well as intraparenchymal hemorrhage, are not uncommon and can result in increased morbidity. Secondary CNS cancers have a higher incidence 5 or more years after allogeneic SCT.

[Pyogenic brain abscesses in adults]

Pyogenic brain abscesses (BA) are rare and their diagnosis may be difficult because of the absence of specific clinical or biological signs. However, the use of diffusion-weighted brain MRI sequences has modified the management of BA, as they are highly sensitive and specific to differentiate pyogenic brain abscesses from necrotic tumors, which are the most frequent differential diagnosis in case of ring-enhancing lesions on CT scan. This new tool allows for a rapid diagnosis and should be followed by a CT-guided aspiration of BA. This safe procedure should be performed if possible before starting antibiotics in order to optimize microbiological diagnosis. Recent epidemiological changes include an increase in the numbers of immunocompromised patients and a decrease in the traditional causes of BA (direct inoculation, ear nose and throat infections, etc.). In consequence, a wider range of bacterial species may be involved, making it all the more necessary to obtain a microbiological diagnosis. Many uncertainties remain in terms of the duration of antibiotic treatment, the optimal radiological follow-up and the place for associated treatments such as corticosteroids and anticonvulsive therapy. BA remain severe infections with high mortality and morbidity rates; the factor most regularly associated with a poor prognosis is the patients neurological status at diagnosis.

Targeting brain cells with glutathione-modulated nanoliposomes: in vitro and in vivo study

Background

The blood–brain barrier prevents many drug moieties from reaching the central nervous system. Therefore, glutathione-modulated nanoliposomes have been engineered to enhance the targeting of flucytosine to the brain.

Methods

Glutathione-modulated nanoliposomes were prepared by thin-film hydration technique and evaluated in the primary brain cells of rats. Lecithin, cholesterol, and span 65 were mixed at 1:1:1 molar ratio. The molar percentage of PEGylated glutathione varied from 0 mol% to 0.75 mol%. The cellular binding and the uptake of the targeted liposomes were both monitored by epifluorescent microscope and flow cytometry techniques. A biodistribution and a pharmacokinetic study of flucytosine and flucytosine-loaded glutathione–modulated liposomes was carried out to evaluate the in vivo brain-targeting efficiency.

Results

The size of glutathione-modulated nanoliposomes was <100 nm and the zeta potential was more than −65 mV. The cumulative release reached 70% for certain formulations. The cellular uptake increased as molar percent of glutathione increased to reach the maximum at 0.75 mol%. The uptake of the targeted liposomes by brain cells of the rats was three times greater than that of the nontargeted liposomes. An in vivo study showed that the relative efficiency was 2.632±0.089 and the concentration efficiency was 1.590±0.049, and also, the drug-targeting index was 3.670±0.824.

Conclusion

Overall, these results revealed that glutathione-PEGylated nanoliposomes enhance the effective delivery of flucytosine to brain and could become a promising new therapeutic option for the treatment of the brain infections.

Infektionen

In diesem Kapitel werden zunächst die für die Neurointensivmedizin wesentlichen bakteriellen Infektionen (Meningitis, spinale und Hirnabszesse, Spondylodiszitis, septisch-embolische Herdenzephalitis) abgehandelt, die trotz gezielt eingesetzter Antibiotika und neurochirurgischer Therapieoptionen noch mit einer erheblichen Morbidität und Mortalität behaftet sind. Besonderheiten wie neurovaskuläre Komplikationen, die Tuberkulose des Nervensystems, Neuroborreliose, Neurosyphilis und opportunistische Infektionen bei Immunsuppressionszuständen finden hierbei besondere Berücksichtigung. Der zweite Teil dieses Kapitels behandelt akute und chronische Virusinfektionen des ZNS sowie in einem gesonderten Abschnitt die HIVInfektion und HIV-assoziierte Krankheitsbilder sowie Parasitosen und Pilzinfektionen, die in Industrieländern seit Einführung der HAART bei HIV zwar eher seltener, aber mit zunehmender Globalisierung auch in unseren Breiten immer noch anzutreffen sind.

A rare case of Cytomegalovirus, Scedosporium apiospermum and Mycobacterium tuberculosis in a renal transplant recipient

BACKGROUND

Renal transplant recipients are at high risk of developing multiple infections, often concomitantly because of their immunocompromised status. Post renal transplant infections are often elusive and require extensive evaluation for proper diagnosis and treatment. A high index of suspicion is required and an attempt should be made to confirm the microbiological diagnosis from each site involved to rule out multiple infections.

CASE PRESENTATION

We report a 50-year-old female, a renal allograft recipient who presented with left hemiplegia, esophageal ulcers and fever 3 months after her transplant. Esophageal biopsy revealed Cytomegalovirus (CMV) inclusions and the whole blood quantitative CMV polymerase chain reaction (PCR) was positive. Neuroimaging showed a brain abscess, stereotactic biopsy from which revealed Scedosporium apiospermum on fungal culture. Her tacrolimus and mycophenolate were stopped and she was managed with intravenous ganciclovir and voriconazole. With these measures, she showed marked improvement in her general and neurological condition. Two months later, she developed recurrence of fever with dry cough. Radiological investigation revealed a cavitating lung lesion, a needle aspiration from which demonstrated acid-fast bacilli. She was started on antituberculous treatment. With these measures, she recovered completely and maintained good graft function despite being on only prednisolone 10 mg once a day.

CONCLUSION

Although CMV disease is not uncommon in the first three months post transplant, Scedosporium is a rare cause of brain abscess. On the other hand, tuberculosis is common in transplant recipients, especially in developing countries, like India. However, this is the first case report of occurrence of these three infections in the same patient, demonstrating the importance of a good microbiological work-up from each site involved in immunosuppressed subjects.

In vitro interactions of amantadine hydrochloride, R-(-)-deprenyl hydrochloride and valproic acid sodium salt with antifungal agents against filamentous fungal species causing central nervous system infection

The mortality rates of fungal infections that affect the central nervous system are high in consequence of the absence of effective antifungal drugs with good penetration across the blood-brain barrier and the blood-cerebrospinal fluid barrier. In the present work in vitro antifungal activities of three good penetrating non-antifungal drugs (amantadine hydrochloride, R-(-)-deprenyl hydrochloride, valproic acid sodium salt) and their combinations with three antifungal agents (amphotericin B, itraconazole, terbinafine) were tested with broth microdilution method against eight fungal isolates belonging to Zygomycetes (Lichtheimia corymbifera, Rhizomucor miehei, Rhizopus microsporus var. rhizopodiformis, Saksenaeavasiformis) and Aspergillus genus (A. flavus, A. fumigatus, A. nidulans, A. terreus). These are known to be possible agents of central nervous fungal infections (CNFI). When used alone, the investigated nonantifungal drugs exerted slight antifungal effects. In their combinations with antifungal agents they acted antagonistically, additively and synergistically against zygomyceteous isolates. Primarily antagonistic interactions were revealed between the investigated drugs in case of Aspergilli, but additive and synergistic interactions were also observed. The additive and synergistic combinations allowed the usage of reduced concentrations of antifungal agents to inhibit the fungal growth in our study. These combinations would be a basis of an effective, less toxic therapy for treatment of CNFI.

Epidemiology of central nervous system infection

In cases of central nervous system infection, it is crucial for the neuroradiologist to provide an accurate differential diagnosis of the possible pathogens involved so that treating physicians can be aided in the choice of empiric therapy. This approach requires the radiologist to be aware of local epidemiology and have knowledge of infectious agents that are endemic to their area of practice. This article reviews and discusses the changing epidemiology of pathogens most often observed in meningitis, brain abscess, epidural abscess, postoperative infections, and human immunodeficiency virus infection.

Infektionen

Trotz Weiterentwicklung moderner Antibiotika in den letzten Jahren sind die Letalitätszahlen der bakteriellen (eitrigen) Meningitis weiterhin hoch; Überlebende haben häufig neurologische Residuen. Die ungünstigen klinischen Verläufe der bakteriellen Meningitis sind meist Folge intrakranieller Komplikationen, wie z. B. eines generalisierten Hirnödems, einer zerebrovaskulären arteriellen oder venösen Beteiligung oder eines Hydrozephalus.

Infections in Leukemia and Hematopoietic Stem Cell Transplantation

Infections are one of the most common complications in patients diagnosed with leukemia and serve as a major obstacle to treatment. Through the early 1970s, infections were the most common cause of death in patients diagnosed with acute leukemia, but improvement in treatment and supportive care over the past few decades, coupled with expanded prophylaxis and prevention regimens, have led to reduction in both the frequency and severity of infections. Regardless, due in part to an aging cancer population and the diversity of cancer treatments and procedures, infectious diseases remain a major cause of morbidity and mortality in patients with leukemia.

Necessary and sufficient role for T helper cells to prevent fungal dissemination in allergic lung disease

Mucosal immune responses to fungal infection range from T helper type 2 (Th2) cell-directed allergic inflammation to Th1-predominant neutrophilic inflammation, but the mechanisms directing these divergent mucosal immune outcomes and the role of T cells in host defense against mucosal fungal infections are not known. Here we examined the mouse mucosal immune responses to 12 filamentous environmental fungal species over a broad range of exposure doses and determined the requirement of T cells for host defense. For all tested fungi, low-grade conidium exposures induced Th2- and eosinophil-predominant allergic lung disease, whereas higher exposures led to rapid conversion to neutrophil- and Th1 cell-predominant inflammation, a phenomenon we term immune phenotype switching. All fungal exposure doses were further linked to the secretion of interleukin-17A (IL-17A). Fungal infections with Curvularia lunata and Aspergillus fumigatus were typically confined to the airway during allergic inflammation but became locally invasive and disseminated to the brain at higher conidium challenge doses, in association with predominant Th1 responses. Fungal dissemination occurred at relatively low challenge doses with the conidia of Aspergillus fumigatus administered to recombinase activating gene 1 (Rag-1)-deficient mice, which lack B and T cells, but B cell-deficient μMT mice and T helper cell-reconstituted Rag-1-deficient mice were comparable to wild-type mice in preventing fungal dissemination. Our findings demonstrate that Th2 cell-predominant allergic responses followed by immune phenotype switching and fungal dissemination are highly predictable outcomes with progressive fungal infectious burdens and that T helper cell responses are protective against lethal fungal dissemination.

Analytic Review: Neurological Complications of Transplantation

Recipients of solid organ or hematopoietic cell transplants are at risk of life-threatening neurological disorders including encephalopathy, seizures, infections and tumors of the central nervous system, stroke, central pontine myelinolysis, and neuromuscular disorders—often requiring admission to, or occurring in, the intensive care unit (ICU). Many of these complications are linked directly or indirectly to immunosuppressive therapy. However, neurological disorders may also result from graft versus host disease, or be an expression of the underlying disease which prompted transplantation, as well as injury induced during radiation, chemotherapy, surgery, and ICU stay. In rare cases, neuroinfectious pathogens may be transmitted with the transplanted tissue or organ. Diagnosis may be a challenge because clinical symptoms and findings on neuroimaging lack specificity, and a biological specimen or tissue diagnosis is often needed for definitive diagnosis. Management is centered on preventing further neurological injury, etiology-targeted therapy, and balancing the benefits and toxicities of specific immunosuppressive agents.

Cerebral phaeohyphomycosis--a cure at what lengths?

Cerebral phaeohyphomycosis is a fungal infection of the brain typically caused by Cladophialophora bantiana, Exophiala dermatitidis, and Rhinocladiella mackenziei, all of which belong to the order Chaetothyriales. The disease results in black, necrotic brain tissue, black pus, and black cerebrospinal fluid. Pathogens usually reach the brain through the bloodstream or lymphatic fluid and occasionally through direct spreading or accidental inoculation. Patients can present with hemiparesis, tonic spasm, headache, fever, sensory variation, cerebral irritation, and even psychotic behavioural changes. Radiological images are characterised by ring-enhanced signs and hyperdense and hypodense lesions. Pathological features frequently include black-to-brown necrotic tissue or dark-coloured pus, granulomatous inflammation, giant cell vasculitis, and pigmented fungal elements, which are easily seen on a direct potassium hydroxide smear, a rapid method for diagnosis. Black fungi can be cultured from a biopsy specimen. Combined antifungal chemotherapy, surgical debridement, and careful immunological interventions are strongly recommended to eradicate these intractable infections.

Cerebral aspergillosis: tissue penetration is the key

Cerebral aspergillosis is increasingly recognized in severely immunocompromised patients and, until recently, this type of fungal infection was associated with a mortality approaching 100%. The central nervous system is a protected environment and penetration of drugs across the blood-brain barrier is mainly limited by their molecular size and physicochemical properties, as well as drug interaction with transporter systems (e.g., P-glycoprotein) at the blood-brain barrier. Most antifungal agents are large molecules (>700 Da), which makes sufficient penetration into the central nervous system unlikely. In fact, the available data indicate low levels of most antifungal agents in cerebrospinal fluid and brain tissue, except for fluconazole and voriconazole. Concentrations of voriconazole exceeding inhibitory concentrations for Aspergillus species were found repeatedly in cerebrospinal fluid and brain tissue, including brain abscess material. A recent retrospective study confirmed that voriconazole treatment resulted in improved response and survival rates in patients with cerebral aspergillosis. Data from animal models, which explored escalated doses or combinations of antifungal agents in experimental neuroaspergillosis, suggest that selected combination or dose-escalated therapies might further improve the still unsatisfactory prognosis in this particular type of Aspergillus infection.

Toll-like receptors in brain abscess

Brain abscesses arise from a localized parenchymal infection, typically elicited by pyogenic bacteria such as Staphylococcus aureus. Despite improvements in detection and treatment strategies, brain abscesses continue to occur, with an increased prevalence in developing countries and immune-compromised patients. Adding to the seriousness of these infections is the recent emergence of antibiotic-resistant strains of bacteria, which are becoming more commonly associated with brain abscesses. Recent studies using a mouse experimental brain abscess model have revealed a complex role for Toll-like receptors (TLRs) in disease pathogenesis. Interestingly, TLR2 has limited impact on the innate immune response during the acute stage of brain abscess formation induced by S. aureus but influences adaptive immunity. In contrast, mice deficient in MyD88, a central adapter molecule for the majority of TLRs in addition to the IL-1R and IL-18R, demonstrate severe defects in innate immunity coupled with exaggerated tissue destruction. It is envisioned that understanding the roles for TLRs in both resident CNS glia as well as infiltrating immune cells will provide insights into how the immune response to bacterial infection can be tailored to achieve effective pathogen destruction without inducing excessive bystander damage of surrounding noninfected brain parenchyma. A discussion of recent findings in this field is presented along with outstanding questions and the concept of a pathogen-necrosis-autoantigen triad for the amplification of TLR signaling is introduced.

Fungal brain infections

PURPOSE OF REVIEW

Fungal infections of the central nervous system, once a relatively rare occurrence, are increasingly common due to the expansion of immunocompromised populations at risk, and therefore are important to recognize early and manage appropriately.

RECENT FINDINGS

The specific infectious risk posed by novel immune-modifying therapies can, in most cases, be predicted on the basis of the immune target and medication timing. In addition, major advances in noninvasive diagnostic tests (e.g. serum beta glucan and galactomannan assays), and the recent introduction of more effective antifungal therapies, have led to a dramatic improvement in clinical outcomes.

SUMMARY

The current review provides approaches to patients with suspected central nervous system fungal infections based on host-risk factors, clinical syndromes and specific pathogens.

Umbilical cord blood transplantation: basic biology and clinical challenges to immune reconstitution

Allogeneic stem cell transplantation has continued to evolve as a common procedure for the treatment of hematological malignancies and bone marrow failure. Donor bone marrow and mobilized peripheral stem cells are routinely employed for the reconstitution of immune function in leukemia and lymphoma patients following radiation and/or chemotherapy. Unfortunately, only 30% of patients have an HLA-identical sibling donor and the identification of matched unrelated donors, particularly for minorities, can present an exceptional challenge. The transplantation of umbilical cord blood (UCB) represents the most recent strategy to expand the potential donor pool while maintaining an acceptable level of treatment-related complications. First utilized in children, UCB transplantation permits a higher degree of HLA disparity while demonstrating a reduction in the incidence and severity of graft-versus-host disease (GvHD) compared to previous transplantation modalities. Despite the apparent decrease in GvHD, relapse rates remain comparable to transplantation with bone marrow or mobilized peripheral blood suggesting a strong graft-versus-leukemia/lymphoma (GvL) effect. However, several issues complicate the use of UCB transplantation and its extension to the treatment of adults. Many infections that afflict transplant patients are particularly frequent and more severe in the context of UCB transplantation. UCB T-cells are naive and therefore display less proliferation and IFN-gamma production in response to cognate antigen and also appear to demonstrate defects in signal transduction mechanisms. In addition, UCB contains T regulatory cells (Treg) with more potent suppressor function than adult Treg. Furthermore, adult patients often require more total cells and CD34+ progenitors for transplantation than a single UCB unit can provide. Thus, strategies to expand selected subpopulations from UCB and the use of multi-unit transplantation are areas of active research. This review will provide a condensed summary of the clinical history of UCB transplantation and emphasize the advantages and disadvantages of this approach to hematological malignancies in comparison to other methods of hematopoietic stem cell transplantation. Subsequently, it will mainly focus on the current challenges to immune reconstitution presented by UCB transplantation, recent research into their cellular and molecular mechanisms, and experimental approaches to overcome them.

Poor efficacy of amphotericin B-based therapy in CNS aspergillosis

Recently, improved response and survival rates in patients treated with voriconazole and neurosurgery for central nervous system (CNS) aspergillosis have been reported. We assessed retrospectively the outcome in 17 patients with definite or probable CNS aspergillosis treated with amphotericin B alone (n = 15) or in combination with 5-fluorocytosine (n = 3) or itraconazole (n = 2). Four patients underwent neurosurgery. The mortality rate was 100% with a median survival of only 10 days (range: 3-60) after onset of first symptoms or first radiological evidence of CNS aspergillosis. In conclusion, treatment with amphotericin B and itraconazole has negligible efficacy in CNS aspergillosis.

Fungal CNS infections in patients with hematologic malignancy

Various fungal agents can cause CNS infections. CNS fungal infections may present as a mass (i.e., brain abscess) typically in the course of aspergillosis or zygomycosis, or may primarily involve the meninges (i.e., meningitis), as can be observed in patients with candidiasis or cryptococcosis. Most commonly, fungal brain abscesses are due to aspergillosis. CNS aspergillosis is observed particularly in acute leukemia and allogeneic hemopoietic stem cell transplantation patients. Usually, aspergillosis is localized in the lungs and secondarily spreads to the brain; only in few cases does it develop as solitary localization of CNS. In these conditions, diagnosis is very difficult because signs and symptoms can be completely aspecific. Diagnosis can often be performed only through aggressive procedures (i.e., stereotactic puncture). Zygomycetes are the second most frequent cause of brain abscesses. CNS involvement is higher than in the course of invasive aspergillosis, and this fungal complication is also characterized by a high mortality rate. In vitro and in vivo studies demonstrated that only posaconazole and lipid formulations of amphotericin B present some possibility of success in the treatment of zygomycosis, but the pharmacologic approach should always be associated with surgery. Among molds, other agents (i.e., Fusarium and Scedosporium) may also be responsible for fungal abscess. More rarely during the course of a hematologic malignancy, a meningeal candidiasis or cryptococcosis may be observed. This review mainly focuses on the epidemiology, clinical manifestations, diagnosis and management strategies of all cases of CNS fungal infections in hematologic patients.

The invasive and saprophytic syndromes due to Aspergillus spp

Aspergillus spp. produce a wide range of invasive and sapropytic syndromes which may involve any tissue. Within a given tissue or organ the pathology and pathogenesis varies enormously, ranging from angioinvasive disease to noninvasive saprophytic disease. The individual invasive and saprophytic syndromes in which a causative role can be attributed to Aspergillus spp. are detailed specifically with reference to the underlying pathology and pathogenesis, the clinical setting and features, and the manner in which a diagnosis can be established.

Successful treatment with voriconazole of fungal cerebral abscess due to Cladophialophora bantiana

We report the first successfully treated case of Cladophialophora bantiana cerebral abscess with the relatively new antifungal agent voriconazole. Infection with this organism is often fatal. A 64-year-old man presented to our institution with progressive neurologic symptoms due to a brain abscess. A stereotactic brain biopsy confirmed the pathogen as C. bantiana. We discuss the successful treatment of this patient, and review the pharmacological actions of voriconazole and the literature on the treatment of this organism. Previously considered a rare cause of cerebral abscess, C. bantiana fungal infections have become more common in recent years. Aggressive and continuous treatment with voriconazole may offer an improved chance of survival in these patients.

Pulmonary aspergillosis with possible cerebral involvement in a previously healthy pregnant woman

Invasive aspergillosis is observed mainly in immunodepressed patients. Here we report a case of pulmonary aspergillosis with CNS involvement in a pregnant woman without other known causes of immunodeficiency.

CASE REPORT

A 23-years old pregnant woman underwent a caesarean because of unexplained seizures. During the subsequent days worsening headache and a deteriorating neurological status were reported suggesting meningitis. Stiffness, right sided hemiparesis and cranial nerve palsies were observed at admission. Radiological findings revealed lesions involving the right pulmonary apex, the right cerebellar hemisphere and the Pterygopalatina fossa. Microbiological studies revealed large colonies of Aspergillus fumigatus. A favorable outcome was observed after administration of liposomal amphotericin B and 5-fluorocytosine and, at improved conditions, when oral uptake of itraconazole was given. The authors conclude that risk of infections sustained by fungal opportunistic agents during pregnancy must be considered. Sequential antifungal administration may be an efficient therapy able to shorten hospitalization.

Infections of the central nervous system by melanized fungi: a review of cases presented between 1999 and 2004

Several types of infections of the central nervous system by melanized fungi can be distinguished: (a) single-organ infection of the cerebrum, (b) extension into the cerebrum from adjacent cavities, (c) fungal presence in the cerebrospinal fluid, or (d) meningitis. The fungal order Chaetothyriales (containing Exophiala-like black yeasts and relatives) is particularly rich in fungi causing cerebral infections. Cases by the main agents, Cladophialophora bantiana, Exophiala dermatitidis, and Ramichloridium mackenziei, published during the last 5 years are reviewed. Most of these infections prove to be fatal. Resection of the lesions in combination with antimycotic therapy may reduce mortality.

Intracerebral abscess in children: historical trends at Children's Hospital Boston

OBJECTIVES

A previous study performed at Children's Hospital Boston describing the natural history of intracerebral abscess between 1945 and 1980 demonstrated a decline in mortality after 1970. This current study examines the occurrence of intracerebral abscess at Children's Hospital Boston between 1981 and 2000, inclusive, and compares the results with the previous study. Our objectives were to determine whether there had been a change in the predisposing factors, whether there were changes in the microbiology of intracerebral abscesses, and whether mortality rate had continued to decline.

METHODS

To ensure that all occurrences of intracerebral abscess treated at Children's Hospital Boston between 1981 and 2000 were identified, we searched 4 separately maintained databases for the keywords "brain" or "abscess" or the International Classification of Diseases, Ninth Revision code 324.x. This search yielded the names of 386 patients. Of these 386 patients, a solitary intracerebral abscess or multiple noncontiguous intracerebral abscesses could be confirmed in 54 patients on the basis of cranial imaging (computed tomography or magnetic resonance imaging) or autopsy reports. The complete retrospective review of the medical records of these 54 patients constitutes the basis for this study.

RESULTS

Congenital heart disease was the most common predisposing factor during both eras. Compared with the previous era, important historical trends identified include a reduction in the number of abscesses that occurred in the settings of sinus or otitic infection (11% during 1981-2000 vs 26% during 1945-1980), an increase in number of intracranial abscesses in infants (18% vs 7%) and in the setting of immunosuppression (16% vs 1%), an increase in the number of children who were treated with antibiotics alone (22% vs 1%), a stable overall mortality rate (24% vs 27%), and the identification of Citrobacter and fungus as causes of intracranial abscess not observed during the previous era of 1945-1980. Citrobacter was observed only during the neonatal period. Fungi were the causative organisms predominantly in the setting of immunosuppression.

CONCLUSIONS

Intracerebral abscess in children continues to be associated with high rates of neurologic impairment and death. Because earlier detection may reduce morbidity and mortality, intracranial abscess should be considered when evaluating children with new-onset neurologic signs or symptoms, especially in children who have acute immunosuppression and disseminated fungal disease or fungemia.