July 2021 – Clinical Microbiology / Infectious Disease Pathology

The correct answer is: Cladophialophora bantiana.

Cladophialophora bantiana, a dematiaceous fungus, is the most common causative agent of cerebral phaeohyphomycosis (1). C. bantiana is found worldwide, although its exact ecological niche is still unknown. Infections can be caused by minor traumatic implantation, but pulmonary and disseminated disease is caused by the inhalation of conidia (1, 3). C. bantiana, like other dematiaceous fungi, is pigmented due to the presence of melanin in its cell walls. C. bantiana grows well on standard fungal media and produces dark colonies with a velvet-like texture and discreetly grooved topography (Image 3). Cellophane tape preparations of the colonies show long chains of smooth, lemon-shaped conidia (Image 4). Although species-level identification can be made using these classic morphologic features, identification of C. bantiana using MALDI-TOF mass spectrometry or sequencing from early fungal growth is generally faster and safe for lab staff because identification often can occur prior to production of the mature, infectious conidia. Culture plates should be taped securely shut and the organism inactivated by autoclaving.

In a review of 101 cases of phaeohyphomycosis, C. bantiana was the most common agent of CNS infections and uniquely, a majority (73%) of the patients were immunocompetent, but it can also infect immunocompromised patients (2). A majority of the patients presented with brain abscesses. Clinical symptoms amongst the patients were varied, and typical symptoms included headache, neurologic deficits, and seizures, although rarely all three were present. Almost all of the patients (86%) were diagnosed based on histopathological findings. Overall mortality rate amongst the patients was 70%. There is no standard therapy for the treatment of C. bantiana CNS infections, but better outcomes were observed in patients who underwent complete excision of the abscess (2). Combination therapy of AmBisome, flucytosine and itraconazole has also shown improved treatment efficacy. This patient was treated with a combination of AmBisome, flucytosine and voriconazole. Therapeutic drug monitoring of voriconazole and follow-up genetic testing determined that the patient was a rapid metabolizer and omeprazole was added to increase serum concentrations of voriconazole.  

In tissues, dematiaceous fungi usually have a characteristic appearance of irregularly swollen hyphae with yeast like structures in contrast to Aspergillus species which typically show septate, acutely branching, straight walled hyphae (3). It can be difficult to distinguish Aspergillus and dematiaceous fungi based on GMS stains, but pigmentation visible on H&E stains or melanin-specific Masson-Fontana stains can also help distinguish dematiaceous fungi from other moulds. 

Rhinocladiella mackenziei is also a pigmented fungus that can cause human cerebral phaeohyphomycosis but is endemic solely to the Middle East (1). Phialophora species are dematiaceous fungi that most commonly cause chromoblastomycosis (1). Traumatic implantation of these organisms cause cutaneous or subcutaneous infections with warty, tumor-like, or cauliflower-like lesions. Unlike C. bantiana, in tissues Phialophora species seen as sclerotic bodies which are brownish, muriform, septated cells also coined as “copper penny bodies.”

References

1. Revankar et al. Melanized Fungi in Human Disease. 2010. Clin Microbiol Rev. 23(4): 884-928
2. Revankar et al. Primary Central Nervous System Phaeohyphomycosis. CID 2004. 38(2) 206-216
3. Bryan H. Schmitt and Bobbi S. Pritt Pathology of Infectious Diseases, 25, 516-530