CNS fungal infections: A review

Disseminated granulomatous encephalitis caused by Schizophyllum commune in a dog with severe neurological signs

A 10-year-old spayed mixed breed dog presented with severe neurological signs. Computed tomography revealed a cranial mediastinal mass, osteolysis of the right second rib and second thoracic vertebra, tracheobronchial and mesenteric lymph node enlargement, pneumonia and pleural effusion. Magnetic resonance imaging detected lesions in the white matter of the right frontal lobe and left cerebral hemisphere with contrast-enhanced T1-weighted images showing demarcated enhancement. On cut section, the surface of the right cerebral frontal lobe and left cerebral hemisphere corticomedullary junctions were indistinct and the white matter was discoloured. Microscopically, multicentric granulomatous inflammation was seen in the brain, cranial mediastinal mass, masses on the right second rib, tracheobronchial and mesenteric lymph nodes, heart, kidneys, lungs and oesophagus. Necrosis and hyaline fungal structures were frequently observed in the centre of the granulomas. These fungi had septae, Y-shaped branching and were 2-3 μm in width. Sequence analysis of DNA from formalin-fixed paraffin-embedded samples identified the fungi as Schizophyllum commune. Based on these findings, this case was diagnosed as disseminated S. commune infection. This is the first report of granulomatous encephalitis caused by S. commune in a dog.

From Skin and Gut to the Brain: The Infectious Journey of the Human Commensal Fungus Malassezia and Its Neurological Consequences

The human mycobiome encompasses diverse communities of fungal organisms residing within the body and has emerged as a critical player in shaping health and disease. While extensive research has focused on the skin and gut mycobiome, recent investigations have pointed toward the potential role of fungal organisms in neurological disorders. Among those fungal organisms, the presence of the commensal fungus Malassezia in the brain has created curiosity because of its commensal nature and primary association with the human skin and gut. This budding yeast is responsible for several diseases, such as Seborrheic dermatitis, Atopic dermatitis, Pityriasis versicolor, Malassezia folliculitis, dandruff, and others. However recent findings surprisingly show the presence of Malassezia DNA in the brain and have been linked to diseases like Alzheimer's disease, Parkinson's disease, Multiple sclerosis, and Amyotrophic lateral sclerosis. The exact role of Malassezia in these disorders is unknown, but its ability to infect human cells, travel through the bloodstream, cross the blood-brain barrier, and reside along with the lipid-rich neuronal cells are potential mechanisms responsible for pathogenesis. This also includes the induction of pro-inflammatory cytokines, disruption of the blood-brain barrier, gut-microbe interaction, and accumulation of metabolic changes in the brain environment. In this review, we discuss these key findings from studies linking Malassezia to neurological disorders, emphasizing the complex and multifaceted nature of these cases. Furthermore, we discuss potential mechanisms through which Malassezia might contribute to the development of neurological conditions. Future investigations will open up new avenues for our understanding of the fungal gut-brain axis and how it influences human behavior. Collaborative research efforts among microbiologists, neuroscientists, immunologists, and clinicians hold promise for unraveling the enigmatic connections between human commensal Malassezia and neurological disorders.

Case Report: Successful Treatment of Recurrent Candida Albicans Meningitis with Kimura's Disease Using Amphotericin B Colloidal Dispersion Combined with Fluconazole

Background

Candida albicans meningitis is a fungal infectious disease of the central nervous system that most often occurs in immunodeficient populations. Kimura's disease is an IgE-mediated inflammatory reactive disease that is a chronic immune disorder with predominantly lymph node, soft tissue, and salivary gland damage, the treatment of which is hormone-based. The combination of Kimura's disease with C. albicans meningitis is relatively uncommon. Herein, we report a case of C. albicans meningitis in combination with Kimura's disease.

Case Presentation

The case is a 26-year-old male with a medical history of Kimura, who presented with symptoms of dizziness, headache, and double vision. Lumbar puncture and cerebrospinal fluid examination revealed an increased white blood cell count. Further analysis through cerebrospinal fluid culture and metagenomic second-generation sequencing (mNGS) led to the final diagnosis of C. albicans meningitis. The patient was treated with fluconazole after the onset of C. albicans meningitis and had a good response. During the treatment, changes in the pathogen genome sequences were monitored dynamically using metagenomic next-generation sequencing. After 1 year, the patient had a recurrence of Candida meningitis. Treatment with fluconazole alone was ineffective, while antifungal treatment with amphotericin B colloidal dispersion was effective with no detectable renal injury.

Conclusion

Candida meningitis can occur in the context of Kimura disease. In patients with mild disease, the possibility of recurrence exists with fluconazole treatment alone, and the efficacy of amphotericin B colloidal dispersion combined with fluconazole is better than fluconazole alone in patients with a recurrence. No nephrotoxicity was observed during amphotericin B colloidal dispersion treatment. The mNGS allows dynamic monitoring of pathogen sequencing reads, and for Candida meningitis, there may be a mismatch between peak sequencing reads and disease during treatment, the basis for which is unclear.

ß-D-Glucan Assay in the Cerebrospinal Fluid for the Diagnosis of Non-cryptococcal Fungal Infection of the Central Nervous System: A Retrospective Multicentric Analysis and a Comprehensive Review of the Literature

BACKGROUND

Except for cryptococcosis, fungal infection of the central nervous system (FI-CNS) is a rare but severe complication. Clinical and radiological signs are non-specific, and the value of conventional mycological diagnosis is very low. This study aimed to assess the value of β1,3-D-glucan (BDG) detection in the cerebrospinal fluid (CSF) of non-neonatal non-cryptococcosis patients.

METHODS

Cases associated with BDG assay in the CSF performed in 3 French University Hospitals over 5 years were included. Clinical, radiological, and mycological results were used to classify the episodes as proven/highly probable, probable, excluded, and unclassified FI-CNS. Sensitivity and specificity were compared to that calculated from an exhaustive review of the literature.

RESULTS

In total, 228 episodes consisting of 4, 7, 177, and 40 proven/highly probable, probable, excluded, and unclassified FI-CNS, respectively, were analysed. The sensitivity of BDG assay in CSF to diagnose proven/highly probable/probable FI-CNS ranged from 72.7% [95% confidence interval {CI}: 43.4%‒90.2%] to 100% [95% CI: 51%‒100%] in our study and was 82% in the literature. For the first time, specificity could be calculated over a large panel of pertinent controls and was found at 81.8% [95% CI: 75.3%‒86.8%]. Bacterial neurologic infections were associated with several false positive results.

CONCLUSIONS

Despite its sub-optimal performance, BDG assay in the CSF should be added to the diagnostic armamentarium for FI-CNS.

Recent Advances in Pharmaceutical Approaches of Antimicrobial Agents for Selective Delivery in Various Administration Routes

Globally, the increase of pathogenic bacteria with antibiotic-resistant characteristics has become a critical challenge in medical treatment. The misuse of conventional antibiotics to treat an infectious disease often results in increased resistance and a scarcity of effective antimicrobials to be used in the future against the organisms. Here, we discuss the rise of antimicrobial resistance (AMR) and the need to combat it through the discovery of new synthetic or naturally occurring antibacterial compounds, as well as insights into the application of various drug delivery approaches delivered via various routes compared to conventional delivery systems. AMR-related infectious diseases are also discussed, as is the efficiency of various delivery systems. Future considerations in developing highly effective antimicrobial delivery devices to address antibiotic resistance are also presented here, especially on the smart delivery system of antibiotics.

Invasive Cerebral Aspergillosis in Non-Neutropenic Patients: A Case Series from Western India

PURPOSE

Invasive cerebral aspergillosis (ICA) is a rare but fatal infection affecting neutropenic immunocompromised patients. Recently cases have been reported in non-neutropenic settings also. We hereby present a series of ICA cases in non-neutropenic patients diagnosed at our tertiary care centre in Western India between March to October 2021.

METHODS

All patients with clinico-radiological suspicion of CNS infections were analysed. Data regarding Clinico-radiological features, diagnosis, treatment and outcome were collected. After ruling out bacterial, viral and mycobacterial causes, appropriate samples were sent for KOH (potassium hydroxide) wet mount, fungal culture, histopathology and serum/CSF galactomannan.

RESULTS

A total of four patients were diagnosed with ICA with a mean age of 43.5 years. Three patients had significant comorbidities; Diabetes mellitus, chronic liver disease and COVID-19 pneumonia treated with dexamethasone, respectively. One patient had no known predisposing factor. Radiologically, one patient presented with a frontal brain abscess and two patients had multiple subcortical hyperintensities. Three patients were diagnosed based on CSF galactomannan (Platelia™ Aspergillus antigen, Bio-Rad, France) with OD >1 and one patient had high serum galactomannan (OD >2). CSF culture grew Aspergillus species in two patients. All patients were treated with Voriconazole. One patient recovered, and the remaining three succumbed due to delayed presentation and extensive cerebral involvement.

CONCLUSION

Even in non-neutropenic patients, a high index of suspicion is warranted for cerebral aspergillosis. CSF galactomannan can be considered a reliable marker for diagnosing ICA in non-neutropenic settings. Early diagnosis allows timely antifungal therapy, which could be a key to improving the outcomes.

The roles of fungus in CNS autoimmune and neurodegeneration disorders

Fungal infection or proliferation in our body is capable of initiation of strong inflammation and immune responses that result in different consequences, including infection-trigged organ injury and inflammation-related remote organ dysfunction. Fungi associated infectious diseases have been well recognized in the clinic. However, whether fungi play an important role in non-infectious central nervous system disease is still to be elucidated. Recently, a growing amount of evidence point to a non-negligible role of peripheral fungus in triggering unique inflammation, immune response, and exacerbation of a range of non-infectious CNS disorders, including Multiple sclerosis, Neuromyelitis optica, Parkinson's disease, Alzheimer's disease, and Amyotrophic lateral sclerosis et al. In this review, we summarized the recent advances in recognizing patterns and inflammatory signaling of fungi in different subsets of immune cells, with a specific focus on its function in CNS autoimmune and neurodegeneration diseases. In conclusion, the fungus is capable of triggering unique inflammation by multiple mechanisms in the progression of a body of CNS non-infectious diseases, suggesting it serves as a key factor and critical novel target for the development of potential therapeutic strategies.

Cerebrospinal fluid: a target of some fungi and an overview

Meningitis is a potentially life-threatening infection characterised by the inflammation of the leptomeningeal membranes. The estimated annual prevalence of 8.7 million cases globally and the disease is caused by many different viral, bacterial, and fungal pathogens. Although several genera of fungi are capable of causing infections in the central nervous system (CNS), the most significant number of registered cases have, as causal agents, yeasts of the genus Cryptococcus. The relevance of cryptococcal meningitis has changed in the last decades, mainly due to the increase in the number of people living with human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS) and medications that impair the immune responses. In this context, coronavirus disease 19 (COVID-19) has also emerged as a risk factor for invasive fungal infections (IFI), including fungal meningitis (FM), due to severe COVID-19 disease is associated with increased pro-inflammatory cytokines, interleukin (IL)-1, IL-6, and tumour necrosis factor-alpha, reduced CD4-interferon-gamma expression, CD4 and CD8 T cells. The gold standard technique for fungal identification is isolating fungi in the culture of the biological material, including cerebrospinal fluid (CSF). However, this methodology has as its main disadvantage the slow or null growth of some fungal species in culture, which makes it difficult to finalise the diagnosis. In conclusions, this article, in the first place, point that it is necessary to accurately identify the etiological agent in order to assist in the choice of the therapeutic regimen for the patients, including the implementation of actions that promote the reduction of the incidence, lethality, and fungal morbidity, which includes what is healthy in the CNS.

Transverse myelitis in children and adults

Transverse myelitis is a noncompressive myelopathy of inflammatory origin. The causes are broad, ranging from infective or toxic to immuno-mediated etiology. They can be manifestations of systemic diseases, such as sarcoidosis and systemic lupus erythematous, or phenotypes of neuroinflammation; in a portion of cases, the etiology remains unknown, leading to the designation idiopathic. The clinical presentation of transverse myelitis depends on the level of spinal cord damage and may include sensorimotor deficits and autonomic dysfunction. The age of onset of the disorder can impact the symptoms and outcomes of affected patients, with differences in manifestation and prognosis between children and adults. Spinal cord magnetic resonance imaging and cerebrospinal fluid examination are the main diagnostic tools that can guide clinicians in the diagnostic process, even though the search for antibodies that target the structural components of the neural tissue (anti-aquaporin4 antibodies and anti-myelin-oligodendrocyte antibodies) helps in the distinction among the immune-mediated phenotypes. Management and outcomes depend on the underlying cause, with different probabilities of relapse according to the phenotypes. Hence, immunosuppression is often recommended for the immune-mediated diseases that may have a higher risk of recurrence. Age at onset has implications for the choice of treatment.

Host immune responses in the central nervous system during fungal infections

Fungal infections in the central nervous system (CNS) cause high morbidity and mortality. The frequency of CNS mycosis has increased over the last two decades as more individuals go through immunocompromised conditions for various reasons. Nevertheless, options for clinical interventions for CNS mycoses are still limited. Thus, there is an urgent need to understand the host-pathogen interaction mechanisms in CNS mycoses for developing novel treatments. Although the CNS has been regarded as an immune-privileged site, recent studies demonstrate the critical involvement of immune responses elicited by CNS-resident and CNS-infiltrated cells during fungal infections. In this review, we discuss mechanisms of fungal invasion in the CNS, fungal pathogen detection by CNS-resident cells (microglia, astrocytes, oligodendrocytes, neurons), roles of CNS-infiltrated leukocytes, and host immune responses. We consider that understanding host immune responses in the CNS is crucial for endeavors to develop treatments for CNS mycosis.

Case Report: Cryptococcal eosinophilic meningitis in a patient with Hodgkin lymphoma

Cryptococcal meningitis is the most common fungal meningitis in clinical practice. It primarily occurs in immunocompromised people and is typically associated with human immunodeficiency virus (HIV) infection. In rare cases, it is associated with Hodgkin lymphoma (HL). Eosinophilic meningitis (EM) is characterized by increased eosinophils in the cerebrospinal fluid (CSF) and is often caused by a parasitic infection of the central nervous system (CNS). EM caused by cryptococcal infection is rare; only four cases have been reported in the past 30 years. Here, we report a case of cryptococcal meningitis in a patient with HL who presented with an atypical eosinophil-predominant CSF cytology response. The patient's eosinophil proportion reached 91%; a proportion this high has not been reported previously and may be associated with HL. After antifungal therapy and tumor chemotherapy, the proportion of eosinophils decreased significantly. This case shows that cryptococcal meningitis and HL may be simultaneously contributing to CSF eosinophilia. HL should be considered in patients with eosinophilic cryptococcal meningitis and multiple adenopathies.

Serologic biomarkers in Candida and Aspergillus infections of the central nervous system: a comparison of galactomannan, mannan, and β-1,3-D-gucan testing from serum and cerebrospinal fluid

BACKGROUND

The incidence of Aspergillus and Candida CNS infection, which are characterized by high mortality rates, is underestimated. This underdiagnosis presumably results from the limitations of available diagnostic tools and the need for invasive sampling. Little is known about the role of serologic biomarkers in the setting of CNS aspergillosis and candidiasis.

PATIENTS, MATERIALS, METHODS

Serum (19) and cerebrospinal fluid (CSF; 10) samples of 19 patients, whose CNS specimens yielded growth of Aspergillus or Candida, were analyzed for different biomarkers for fungal infection, i.e., galactomannan (GM), galactomannoprotein (GP), mannan, anti-mannan-antibodies, and β-1,3-D-glucan (BDG). Serum and CSF specimens of time-matched patients (two each for every case of fungal CNS infection) were included as controls.

RESULTS

GM, GP, and BDG seropositivity was found in one, two, and three of five cases of CNS aspergillosis. BDG and mannan / anti-mannan-antibody sensitivity in proven CNS candidiasis was 40 % and 20 %, respectively. Applying the serum cut off, sensitivity in CSF testing was 100 % for GM and BDG, and 50 % for mannans. While serum specificity for all assays ranged from 89 - 97 %, specificity for CSF BDG was only 70 %. No false positive GM results from CSF were obtained.

CONCLUSION

Sensitivity for diagnosing CNS aspergillosis and CNS candidiasis from serum is mediocre for all serological biomarkers. GM testing in CSF proved excellent performance. With a sensitivity of 100 % but a specificity of only 70 %, CSF BDG might be most useful when used in patients with a high pre-test probability.