Pleural aspergillosis is a rare condition, comprising less than 1% of all pleural diseases [6]. It primarily targets immunocompromised individuals, including patients with prolonged neutropenia, recipients of hematopoietic stem cell or solid organ transplants, people with hematological cancers or solid tumors, HIV/AIDS patients, and those who have undergone allogeneic stem cell transplantation. All these groups face a higher risk of infection [7]. Immunosuppression, however, may not be an absolute requirement for the development of pleural aspergillosis. Factors such as the use of thoracic drainage tubes, pneumonectomy procedures, thoracentesis, and scar tissue formation could potentially increase the risk of Aspergillus colonization in the pleura or lungs through environmental or airborne exposure. Importantly, most documented cases of pleural aspergillosis have been observed in patients with underlying conditions or prior pulmonary infections, including tuberculosis (87%), bronchopleural fistula (74%), pleural drainage (56%), or pneumonectomy (17%) [8,9,10]. Chronic exposure to high concentrations of conidia in hot and humid environments may predispose immunocompetent hosts to disease development. In one reported case [11], a patient developed Aspergillus flavus infection following recurrent chronic obstruction of the right upper lobe bronchus, which led to mucus plug formation and impaired luminal drainage and reduced fungal clearance. Although recurrent pneumothorax has been documented as a common predisposing factor (e.g., a patient with a history of multiple pneumothoraces underwent two thoracic drainage procedures, which likely contributed to pleural aspergillosis) [12].
Another rare manifestation in patients with normal immune function is Pancoast syndrome. Pleural aspergillosis is extremely uncommon in individuals with a competent immune system. The first documented case of Pancoast syndrome caused by Aspergillus involved a 22-year-old immunocompetent man who exhibited symptoms of Horner syndrome and weakness in the small muscles of his right hand. Surgical investigation uncovered an abscess-like lesion near the subclavian artery, and pathological analysis confirmed aspergillosis as the underlying cause. The infection was believed to have originated from the inhalation of Aspergillus fumigatus conidia, which subsequently seeded the fungal infection in the apical pleura. Aspergillus likely triggered vasculitis or septic complications, leading to pyogenic embolization [13]. Notably, XY Huang et al. [14] reported a case of a 16-year-old with hydropneumothorax. In this case, pleural effusion mNGS initially suggested Aspergillus infection. Given the exceptional rarity of pleural aspergillosis in immunocompetent individuals, the initial mNGS findings were dismissed. Nevertheless, subsequent thoracoscopic tissue culture verified Aspergillus fumigatus, underscoring the essential role of mNGS as an auxiliary diagnostic method in unclear clinical situations.
In our case, the patient had no history of diseases or treatments associated with immunosuppression, nor any evidence of diabetes, coronary artery disease, or hypertension. The patient was HIV negative and underwent general anti-nuclear antibody testing and vasculitis antigen–antibody testing. Despite initial clinical suspicion of tuberculous pleuritis based on inflammatory markers and imaging findings, the pathological examination of the visceral pleura via medical thoracoscopy revealed granulomatous inflammation. No abnormalities were detected on tissue TB-DNA testing or special staining. Additionally, nucleic acid testing for Mycobacterium tuberculosis and rifampin resistance gene polymorphism analysis (GeneXpert) of bronchoalveolar lavage fluid failed to confirm the presence of tuberculosis. Given the patient had no comorbidities and the clinical ambiguity, empirical anti-tuberculosis therapy was initiated. However, marked eosinophilia and elevated T-lymphocyte subset counts raised suspicion that atypical pathogens or fungal infection might underlie the pleural pathology. To further investigate, mNGS of pleural effusion was performed, and Aspergillus fumigatus (sequence reads: 148) was identified. Given these results, we hypothesized that the infection might have originated from prior invasive thoracic procedures, particularly a thoracentesis performed at a local clinic. After the initiation of voriconazole therapy, repeat chest CT demonstrated resolution of pleural effusion, and over a 12 -month follow-up, sustained remission was confirmed. These findings supported the efficacy of antifungal treatment and reinforced A. fumigatus as the causative agent.
Lucia Ferreiro [15] proposed that the progression of pleural effusion and the application of light criteria can categorize many idiopathic effusions. Techniques such as PCR, pleural effusion culture, and pleural tissue biopsy have improved diagnostic yields [16]. PCR enhances diagnostic accuracy to 74% and improves pathogen detection specificity to 58%. Thoracoscopic pleural biopsy is associated with reduced hospital stays and lower expenses, establishing it as the preferred initial approach for pleural effusion in well-equipped medical facilities [17]. However, although histopathological staining assists in diagnosis, it is unable to determine microbial species or assess drug susceptibility. Thoracoscopy continues to be the gold standard for a definitive pathological diagnosis. In addition, Yan Z et al. [18] conducted a trial that included 35 patients with pulmonary embolism (PE). They analyzed their PE samples using mNGS to evaluate tuberculous pleural effusion (TPE) and malignant pleural effusion (MPE). The study showed that the latest advances mNGS have shown promising applications in the diagnosis of infectious diseases. Gao N et al. [19] retrospectively analyzed 25 patients with pulmonary infections and pleural effusion from July 2020 to December 2021. The research has shown that compared with traditional testing, using mNGS combined with biopsy samples obtained through medical thoracoscopy yields higher positivity rates and provides evidence for precise pathogen identification in patients with infectious pleural effusion.
Traditional diagnostic methods rely heavily on clinicians’ experience for targeted pathogen testing, which is inherently limited. For mNGS, sterile specimens such as blood, pleural effusion, and cerebrospinal fluid are prioritized because they carry a lower risk of contamination and offer a higher likelihood of identifying true pathogens. In this case, pleural effusion mNGS was chosen over sputum or bronchoalveolar lavage fluid due to the patient’s minimal pulmonary lesions and dominant pleural pathology; BAL posed a higher risk of contamination. The mNGS analysis detected Aspergillus fumigatus (148 sequence reads) but no definitive bacterial pathogens. Low-read viruses Beta-papillomavirus type 2 (26 reads) and Human herpesvirus 7 (1 read) were considered unlikely to contribute to clinical manifestations. Based on clinical observations, the patient is an elderly male with normal immunity and no underlying diseases. He only has right-sided pleural effusion and no pulmonary parenchymal lesions. Thoracoscopic biopsy showed inflammatory changes. At this time, the low readings of Aspergillus fumigatus detected by mNGS in the patient’s pleural fluid were in the early stage of the disease and had not yet infiltrated the pulmonary parenchyma. This precisely proves the supplementary diagnosis when accurate pathological and pleural fluid culture results cannot be obtained. Interpreting mNGS results requires incorporating clinical information such as symptoms, imaging findings, previous treatment outcomes, epidemiological data, and the origin of the sample. The number of sequences reads alone is insufficient for diagnosis: high read numbers might indicate contamination or colonization, whereas even low read counts of certain obligate pathogens (e.g., Mycobacterium tuberculosis, Nocardia species, Aspergillus species) should raise clinical suspicion due to their rare presence as commensals. One limitation in this case is the lack of histopathological or culture confirmation for A. fumigatus. Culturing continues to be crucial for verifying molecular results, especially for fungal organisms with unclear clinical relevance. mNGS can also assist in the analysis of some bacterial resistance characteristics. Even though mNGS detection belongs to the qualitative detection category, the sequence height is not equivalent to the pathogen load in the body [20]. It is a powerful supplement and extension to traditional detection methods.
In contrast to traditional pathogen detection methods, mNGS provides substantial benefits. Its quick turnaround time (around 30 h) enables early therapeutic intervention for unclear infections. This can shorten hospital stays, cut down on unnecessary diagnostic costs, and minimize inappropriate antibiotic usage by leveraging precision medicine [21]. mNGS offers direct diagnostic indications for the precise recognition of complex infections. In clinical settings, it has been utilized to identify pulmonary fungal infections in BAL fluid and to diagnose invasive fungal diseases affecting the lungs. The technology is suggested as an essential supplementary diagnostic method for detecting rare pathogens, providing significant information to inform diagnostic methods and treatment plans [22]. For severe pneumonia cases involving co-infections with multiple pathogens (e.g., bacteria, viruses, and fungi such as Pneumocystis, Aspergillus, and Rhizopus), mNGS enables simultaneous detection in a single test. This eliminates the need for multiple sampling procedures and prolonged waiting times [23]. Thus, mNGS integrates the advantages of high diagnostic yield, rapid turnaround time, and targeted detection of recurrent infections.
Nevertheless, this study has several limitations. First, this case lacks pleural pathological biopsy findings, pleural effusion fungal culture results, and drug sensitivity test results. As some patients may develop new drug resistance during the treatment course, continuous monitoring is necessary. Additionally, when interpreting the mNGS report, even if the copy number of a specific pathogen is low, the difficulty in nucleic acid extraction of the fungi should be considered, and its pathogenic potential should not be overlooked.