While fungal infections of the CNS are relatively rare, they have become more common with the increasing number of individuals who are immunocompromised due to HIV/AIDS, immunosuppressive therapies, invasive diagnosis and treatment methods, and organ transplants. CNS fungal infections present many diagnostic and therapeutic challenges and are associated with a high mortality rate.
While immunocompromised patients are the most susceptible to CNS fungal infections, they can also occur in immunocompetent patients undergoing invasive procedures such as neurosurgery and in patients exposed to contaminated devices or drugs. In addition, heavy exposure to fungi in endemic regions can lead to infection in immunocompetent individuals.
CNS infections caused by dimorphic fungi are diverse and their signs and symptoms might be associated with the characteristics of both the host and the infectious fungi, including variations in neurotropism and immunosuppression. Infection with these species is frequently caused by spore inhalation in endemic regions. Predominant clinical characteristics include meningitis, brain or epidural abscesses, spinal cord lesions, meningoencephalitis, and primary lung infection.
Aspergillus infections of the CNS are typically caused by Aspergillus fumigatus and arise through hematogenous spread from the primary sites of infection which is mostly pulmonary, or from contiguous anatomical sites, such as the paranasal sinuses. While symptoms are largely nonspecific, the most common signs include fever, focal neurologic defects, seizures, alterered mental status, and lack of response to broad-spectrum antibiotics. Predominant findings include focal lesions or brain abscesses.
CNS infection with non-aspergillus molds most commonly involve zygomycetes, which typically affect the airways. Other non-aspergillus molds, such as Scedosporium apiospermum, Fusarium, and some phaeo- hyphomycetes are less frequent causes of CNS infection. The predominant clinical characteristics of CNS infection due to non-aspergillus molds include brain abscesses and, less commonly, meningitis and primary infection.
Diagnosis of fungal CNS infection involves microscopic and histopathologic examination, and serologic testing such as:
- Galactomannan antigen testing in CSF showed a sensitivity of 88% and a specificity of 96% for CNS aspergillosis
- CSF antigen testing was found to have a sensitivity of 93% and specificity of 100% for coccidioidal meningitis
- β-D-glucan testing of CSF demonstrated 100% sensitivity and 98% specificity for meningitis caused by Exserohilum rostratum
Molecular tests such as polymerase chain reaction may help to confirm the diagnosis, although most are not standardised and the fast-growing genomic knowledge about fungi requires regular curation of sequence data.
The preferred diagnostic imaging tests for CNS fungal infections are computed tomography (CT) and magnetic resonance imaging (MRI), which facilitate detection of infectious lesions and associated complications and can inform the selection of interventions.
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