Uncharted Territory

A 60-year-old woman presented with fever and headache 2 months after liver transplantation. Her medical history includes well-controlled type 2 diabetes mellitus, hepatitis B virus (HBV) cirrhosis, and recurrent hepatocellular carcinoma (HCC). HCC was diagnosed 3 years ago, and she subsequently underwent a laparoscopic left lateral segmentectomy and microwave ablation for recurrent lesions.

For her transplant, induction immunosuppression was methylprednisolone, followed by a maintenance regimen of tacrolimus, mycophenolate mofetil (MMF), and prednisolone. Pre-transplant testing for the donor and recipient showed seropositivity for both cytomegalovirus (CMV) and Epstein-Barr virus (EBV), while hepatitis C virus serologies were negative. She was prescribed acyclovir and trimethoprim/sulfamethoxazole (TMP/SMZ) prophylaxis. Plasma CMV DNA surveillance showed no evidence of viral replication until her recent visit.

Two months post-transplant (4 weeks prior to presentation), the patient began experiencing intermittent fever and a progressively worsening dull headache, localized to the right temporal region, and radiating toward the ear. Although pain medication provided some relief, the headache persisted, though it did not initially impact her daily activities. Two weeks later (2 weeks prior to presentation), however, the headache in her right temporal area intensified.

Two days before her presentation, she noticed new right-sided facial drooping, persistent headache, and recurrent episodes of fever. Additionally, she reported a chronic cough and significant weight loss. Due to these concerning symptoms, she was presented to the hospital.

This immunosuppressed patient presented with acute to subacute illness characterized by headache, fever, cough and weight loss 2 months after liver transplantation. The constellation of progressive headache and facial weakness suggests a focal process in the central nervous system (CNS), possibly a brainstem event like stroke or mass from post-transplant lymphoma or metastatic HCC. Tacrolimus neurotoxicity (eg, posterior reversible encephalopathy syndrome) is also a possibility. However, the fever and other accompanying symptoms strongly supports an infectious etiology such as brain abscess. Pathogens causing brain abscess include pyogenic bacteria, atypical bacteria (Nocardia spp., Mycobacterium tuberculosis), fungi (Aspergillus spp.), and parasite (Toxoplasma gondii). Moreover, the presence of chronic cough suggests an infectious “lung-brain” syndrome, where the pathogen is acquired through inhalation, causing a primary pulmonary process, and later disseminates to the CNS. Key pathogens associated with infectious “lung-brain” syndrome include Nocardia spp., Aspergillus spp. and other fungi, M. tuberculosis, among others [1, 2]. Weight loss suggests chronic infections (eg, M. tuberculosis) or malignancies.

This illness occurred during intense immunosuppression, heightening the susceptibility to opportunistic infections (eg, CMV, EBV, fungi). Donor-transmitted infections should also be considered during early post-transplant period. TMP/SMZ prophylaxis would have reduced but does not completely eliminate the risk of nocardiosis. Other pathogens that may be prevented by TMP/SMZ prophylaxis includes T. gondii, Listeria monocytogenes, among others. In addition to the aforementioned clinical symptoms, timing since transplant, and antimicrobial prophylaxis, it is essential to obtain exposure history, donor information, and perform a comprehensive physical and diagnostic workup to further refine the differential diagnosis.

The patient resides in Ayutthaya, central Thailand, near fields and ponds, with a dog on the property. She is a retired chef and had engaged in gardening until 3 years prior to her transplant. She denies alcohol, tobacco, tattoos, unpasteurized dairy, or raw meat consumption and has no known exposure to tuberculosis or other infectious diseases. She has not traveled outside her region in Thailand or internationally in the past 3 years.

Her donor, a 19-year-old Thai male, suffered a traumatic subarachnoid and subdural hemorrhage, leading to brain death 17 hours before organ procurement. No other organ recipients have reported post-transplant symptoms such as headache or chronic cough.

Talaromyces marneffei, a dimorphic fungus in tropical Asia, is acquired via inhalation and can cause fever, pneumonia, and disseminated disease in immunosuppressed patients. In transplant recipients, it may present with cytopenias, hepatosplenomegaly, and umbilicated skin papules [1]. Although not endemic to central Thailand, talaromycosis cannot be excluded. Burkholderia pseudomallei, found in wet soils, causes melioidosis through skin contact, inhalation, or ingestion. It manifests with fever, pneumonia, and disseminated abscesses. However, TMP/SMZ prophylaxis would have reduced the risk of melioidosis.

Thailand's high tuberculosis burden places M. tuberculosis high on the differential. Transplant candidates are not routinely screened for TB; therefore, reactivation during immunosuppression remains a major concern. Hypervirulent Klebsiella pneumoniae, more prevalent in Asia, can cause pneumonia with dissemination to the liver or brain, particularly in patients with diabetes, cancer, or immunosuppression.

Her occupational exposure as a chef, contact with a dog, and gardening activities increase the risk of zoonoses (eg, T. gondii, Toxocara spp., Brucella spp., Rhodococcus spp.) and environmental pathogens (eg, Nocardia spp., Aspergillus spp., other fungi, free-living amoebae). Coinfections must also be considered in such a heavily immunosuppressed patient with extensive exposures.

On physical examination, the patient appeared chronically ill, with a temperature of 38.2°C, blood pressure of 162/82 mmHg, heart rate of 94 beats/min, respiratory rate of 14 breaths/min, and oxygen saturation of 98% on ambient air. Lung and cardiovascular examinations were unremarkable. Neurological examination revealed right-sided facial drooping sparing the forehead, mild spastic dysarthria, left leg weakness (motor strength 4/5 on the Medical Research Council scale) and impaired right sided coordination on finger-to-nose testing. No neck stiffness was noted.

Initial investigations showed hemoglobin 8.6 g/dL, hematocrit 25.7%, white blood cell count 2850 cells/mm³ (79.6% neutrophils, 11.5% lymphocytes, 7.1% monocytes, 0.9% eosinophils), and platelet count 148,000/mm³. Liver function tests revealed total bilirubin 0.4 mg/dL, aspartate aminotransferase 39 U/L, alanine transaminase 27 U/L, and alkaline phosphatase 82 U/L. Renal function tests showed a blood urea nitrogen 21 mg/dL and creatinine 1.15 mg/dL. Serum cryptococcal antigen and  Aspergillus galactomannan  antigen were negative.

A chest radiograph revealed a new nodular opacity in the right middle lung. CT imaging of the brain demonstrated multiple rim-enhancing lesions with surrounding vasogenic edema in the right cerebellum and bilateral cerebral hemispheres, each measuring less than 2.5 cm in diameter (Figure 1A). Computed tomography (CT) of the chest with contrast revealed multifocal peribronchial and nodular consolidations with mild bronchiectasis scattered throughout both lungs, as well as multiple discrete pulmonary nodules in the lower lobes and right middle lobe, with the largest measuring up to 0.8 cm (Figure 1B). CT abdomen with contrast revealed no focal hepatic mass or splenomegaly.

Figure 1.

The computed tomography of the brain with contrast revealed multiple thick, rim-enhancing lesions with marked perilesional vasogenic edema involving the right cerebellum and bilateral cerebral hemispheres (A). The computed tomography of the chest showed newly developed pulmonary nodules in the right middle lung, measuring up to 0.8 cm (B).

The physical examination and initial diagnostic investigations confirm the suspected “lung-brain” syndrome. Differential diagnoses include M. tuberculosis, Nocardia spp., B. pseudomallei, T. marneffei and other fungi (eg, Aspergillus spp., Mucor spp., Scedosporium spp., H. capsulatum, others). The absence of skin lesions, lymphadenopathy, and hepatosplenomegaly argues against T. marneffei. A negative serum galactomannan lessens the likelihood of Aspergillus spp. or cross-reacting fungi. Negative serum cryptococcal antigen excludes C. neoformans, barring a prozone phenomenon.

Septic emboli from endocarditis (Staphylococcus spp., Streptococcus spp.) are less likely due to normal cardiac findings and absence of peripheral stigmata. Polymicrobial bacterial infections (eg, Actinomyces spp., Bacteroides spp.) linked to oral sources are unlikely due to no observed risk factors. Allograft-related infections (eg, liver abscess) with dissemination to distant sites are improbable given normal abdominal findings on imaging studies.

A systematic approach to identify the offending pathogen of this “lung-brain” syndrome should include blood cultures (bacteria, fungi, mycobacteria), which should be complemented by serology (eg, beta-D-glucan, H. capsulatum) and molecular tests (eg, nucleic acid amplification test specific for M. tuberculosis, T. marneffei or metagenomic sequencing). Cell-mediated immune assays (eg, QuantiFERON-TB Gold Plus) and serologic antibody detection may yield false negative results due to immunosuppression.

Microbiologic sampling of affected organs is recommended. In this case, multiple pulmonary nodules warrant sputum and bronchoalveolar lavage fluid (BAL) fluid for cultures, microbial stains, antigen detection, and nucleic acid testing (eg, Xpert TB). Transbronchial or transthoracic lung biopsy, if feasible, may provide confirmatory diagnostic data. Because of its invasive nature, brain sampling is often reserved for cases when less invasive tests fail to yield a diagnosis.

Blood and sputum cultures were negative. Sputum staining did not reveal organisms from Gram, acid-fast, or modified acid-fast bacilli stains. Molecular testing for M. tuberculosis and non-tuberculous mycobacteria was negative. Serum cryptococcal antigen, Aspergillus galactomannan antigen, toxoplasma immunoglobulin G, and Interferon-gamma release assay (QuantiFERON-TB Gold Plus) were negative. Melioidosis titer was not performed due to high seroprevalence in the endemic area.

After a thorough discussion, the patient expressed a strong preference to avoid a brain biopsy. Consequently, a transthoracic needle biopsy of the pulmonary lesion in the right middle lung was performed. Lung tissue pathological findings did not reveal any organisms, viral cytopathic change, or granuloma from Grocott's methenamine silver (GMS), periodic acid–Schiff (PAS), acid fast, and modified acid fast bacilli stains. The pathological diagnosis revealed normal alveoli.

Negative blood and sputum cultures effectively exclude melioidosis and other bacterial causes such as Nocardia spp., Klebsiella spp., and Staphylococcus spp. The negative QuantiFERON-TB Gold Plus, AFB smears, and molecular tests argue against M. tuberculosis, although mycobacterial cultures may still yield results after several weeks of incubation.

The multiple pulmonary nodules strongly suggest a fungal infection. Negative fungal blood culture reduces the likelihood of T. marneffei, H. capsulatum, Fusarium spp., and Scedosporium spp., although these tests may not yield a diagnosis for several weeks. Moreover, Aspergillus spp. and agents of mucormycosis (Mucor spp., Rhizopus spp.) are not typically recovered in blood cultures. Fungal antigen tests, like galactomannan and beta-D-glucan, provide quicker, sensitive diagnostics. The negative galactomannan assay lowers the likelihood of disseminated aspergillosis or other cross-reacting fungi. However, these fungal antigen tests do not detect the agents of mucormycosis and many dematiaceous fungi, such as Cladophialophora bantiana, which remains a key consideration due to its neurotropic nature.

The nondiagnostic transthoracic lung biopsy, with negative microbiological stains, cultures and histopathology, raises concerns about potential sampling error. Diagnostic options include repeating the lung biopsy or performing a bronchoscopy with transbronchial biopsy. Alternatively, a biopsy of the brain mass may be considered, after balancing the diagnostic yield with procedural risk. A brain biopsy is particularly crucial for identifying pathogens of “lung-brain” syndrome with only a transient pulmonary phase.

Ultimately, a brain tissue biopsy was performed and this revealed acute inflammation with necrotic tissue, consistent with a brain abscess (Figure 2A). GMS and PAS staining are shown (Figures 2B and 2C). Fontana-Masson staining was negative.

Figure 2.

Brain tissue histopathology with hematoxylin and eosin (H&E) staining demonstrated acute inflammation with necrotic tissue, consistent with a brain abscess (A). Periodic acid–Schiff staining (B) and Grocott's methenamine silver staining (C) revealed septate hyphae with acute-angle branching.

After 2 days of incubation, fungal culture of the brain tissue began growing dark-pigmented molds (Figure 3). The negative Fontana-Masson staining, despite the growth of dark-pigmented fungi, was attributed to variations in melanin production or deposition within the fungal cell wall.

Figure 3.

Brain tissue culture on Sabouraud dextrose agar grew dark mold colonies with dark pigmentation on the reverse of the plate, consistent with dematiaceous mold (A, B, and C).

The brain biopsy confirmed brain abscesses caused by a mold. PAS staining revealed atypical septate hyphae, not consistent with the classic features of Aspergillus spp. or agents of mucormycosis. Fontana-Masson staining should highlight melanin-containing, darkly pigmented hyphae, characteristic of dematiaceous fungi. While histopathology suggested a mold, species identification requires culture and molecular diagnostics.

On Sabouraud dextrose agar, the fungus formed darkly pigmented colonies, suggesting dematiaceous fungi like C. bantiana, a CNS-tropic mold. Additional identification could be achieved through direct microscopy and molecular tools, such as DNA sequencing.

Due to the absence of sporulation, further identification relied on DNA sequencing, which confirmed Chrysocorona lucknowensis. The antimicrobial susceptibility test could not be performed.

The final diagnosis is CNS phaeohyphomycosis from C. lucknowensis with probable pulmonary involvement, confirmed via molecular diagnostics of culture from a brain biopsy. Though not previously reported as a human pathogen, dematiaceous molds can cause brain abscesses in immunosuppressed patients. The infection likely occurred via inhalation, with pulmonary nodules serving as the initial primary sites before dissemination to the CNS (“lung-brain” syndrome). Given the severity of CNS fungal abscesses in immunosuppressed patients, aggressive empiric therapy is recommended. Based on clinical experience with other dematiaceous fungi, a combination of liposomal amphotericin B and voriconazole is a reasonable empiric regimen. Antifungal susceptibility testing should guide targeted treatment, although voriconazole has good activity against dematiaceous fungi and provides good CNS penetration.

Surgical aspiration or resection of abscesses if accessible, and reducing immunosuppressive drugs is crucial for immune function restoration. Voriconazole's CYP3A4 inhibition necessitates tacrolimus dose adjustments and monitoring to avoid toxicity. The prognosis of CNS phaeohyphomycosis is guarded, requiring early diagnosis and aggressive management. Preventive measures include avoiding high-risk exposures, using protective gear, and promptly managing wounds. Enhanced awareness of this infection is critical for early detection and intervention.

Intravenous voriconazole was initiated for disseminated phaeohyphomycosis with pulmonary and CNS involvement due to C. lucknowensis. Significant clinical and radiographic improvement was observed on chest CT after 1 month, prompting a switch to oral voriconazole for outpatient management. After achieving therapeutic drug levels for 2 months, brain and chest imaging showed reduced lesion sizes. The patient remains on voriconazole with monthly drug level monitoring and brain imaging every 3–6 months.

DISCUSSION

Phaeohyphomycosis, caused by dematiaceous fungi, can result in a range of diseases, particularly in solid organ transplant recipients [1–4 ]. This case highlighted a number of difficult decisions faced by the discussant and treating clinicians, ranging from how to most expeditiously and safely establish a diagnosis in this immunocompromised patient to how to construct a treatment regimen for what ended up being an extremely rare human pathogen.

A wide range of infectious and noninfectious processes were initially considered for this patient's lung-brain syndrome, making establishing a diagnosis a priority to help guide empiric treatment. The discussant in this case outlined a stepwise approach that carefully balanced the diagnostic yield of various tests with their associated procedural risks, ranging from noninvasive testing (blood cultures, serology. and fungal biomarkers) to lower-morbidity invasive sampling (lung biopsy) and ultimately higher risk invasive testing (eg, brain biopsy). In pursuing such a strategy, the discussant carefully navigated the competing priorities of rapidly establishing a diagnosis and avoiding procedural morbidity. This cost/benefit analysis of choosing testing modalities is an important part of the management reasoning of infectious diseases (ID) practitioners, especially in cases of high diagnostic uncertainty [5].

The choice of antifungal therapy also represented a reasoning challenge for the discussant and treating team. C. lucknowensis has not previously been documented as a human pathogen, and literature to guide its management is lacking. In scenarios where established treatment guidance does not exist, clinicians may extrapolate management decisions from better studied and analogous situations. For example, C. lucknowensis is closely related to Acrophialophora, which has been reported to cause lung, brain, and corneal infections [6–8] and shows greatest in vitro susceptibility to voriconazole [9], electing to pursue a strategy of broad-spectrum antifungal coverage with liposomal amphotericin and voriconazole with consideration of surgical intervention. Although such a strategy for this particular pathogen was unproven, it had a foundation in what is known about the microbiology of related organisms and the pharmacology of the chosen antifungal agents. Thankfully, this patient showed clinical and radiographic improvement with antifungal treatment, alongside dose reduction of prednisolone and tacrolimus, and MMF discontinuation.

Clinicians often venture into uncharted territory when managing immunocompromised patients with rare infections, where diagnostic uncertainty and absence of established treatment guidelines pose significant challenges. These cases require a stepwise approach that combines clinical judgement and reasoning, advanced diagnostics and empiric antifungal therapy informed by previous experience with similar pathogens. Navigating these diagnostic and therapeutic uncertainties is a critical skill for infectious diseases consultants, particularly when facing uncommon or emerging pathogens in high-risk hosts.

Notes

Author contributions. All authors were involved for critical revision of the manuscript and approved the final version before submission.

Acknowledgments. The authors thank Associate Professor Dr Angsana Phuphuakrat and Associate Professor Siriorn P. Watcharananan, Division of Infectious Diseases, Department of Medicine, Faculty of Medicine Ramathibodi Hospital, Mahidol University, Bangkok, Thailand for critical assistance in patient care.

Ethical considerations.Written informed consent was obtained from the patient.

Financial support. None.

Data availability. Data will be made available upon reasonable request.