Clinical impact of severe chronic kidney disease in patients with non-HIV pulmonary cryptococcosis

Background Pulmonary cryptococcosis is an uncommon infectious disease that can develop in both immunocompromised and immunocompetent patients. Severity of chronic kidney disease (CKD) was reported to be one of the risk factors for pulmonary cryptococcosis, but its clinical characteristics have not been fully assessed. The purpose of this study is to clarify clinical characteristics of severe CKD in patients with pulmonary cryptococcosis. Methods The present study retrospectively investigated 56 patients who had pulmonary cryptococcosis with non-human immunodeficiency virus (HIV) infection and were treated at Saga University Hospital between 2005 and 2018. The clinical characteristics were evaluated and compared between patients with estimated glomerular filtration rate (eGFR) >45 mL/min/1.73m 2 (n = 42) (preserved eGFR) and those with eGFR <45 mL/min/1.73m 2 (n = 14) (declined eGFR). Compared with patients with preserved eGFR, those with declined eGFR had significantly higher rate of disseminated cryptococcosis (p = 0.03); higher percentage of patients who did not recover after treatment (p = 0.02); and more frequent clinical features of fever (p <0.01), pleural effusion (p = 0.03), high white blood cell count (p <0.01) and C-reactive protein (p <0.01), and low level of albumin (p <0.01). Multivariate analysis adjusted by immunosuppressive drug use indicated significant differences of fever (p <0.01), high white blood cell count (p = 0.03), C-reactive protein (p = 0.01) and low level of albumin (p <0.01) in patients with eGFR <45 mL/min/1.73m 2 . and low level of albumin. These results practically contribute to the clinical risk evaluation of with cryptococcosis.


Background
Pulmonary cryptococcosis is an uncommon infectious disease that can develop in both immunocompromised and immunocompetent patients. Severity of chronic kidney disease (CKD) was reported to be one of the risk factors for pulmonary cryptococcosis, but its clinical characteristics have not been fully assessed. The purpose of this study is to clarify clinical characteristics of severe CKD in patients with pulmonary cryptococcosis.

Methods
The present study retrospectively investigated 56 patients who had pulmonary cryptococcosis with non-human immunodeficiency virus (HIV) infection and were treated at Saga University Hospital between 2005 and 2018. The clinical characteristics were evaluated and compared between patients with estimated glomerular filtration rate (eGFR) >45 mL/min/1.73m 2 (n = 42) (preserved eGFR) and those with eGFR <45 mL/min/1.73m 2 (n = 14) (declined eGFR).

Results
Compared with patients with preserved eGFR, those with declined eGFR had significantly higher rate of disseminated cryptococcosis (p = 0.03); higher percentage of patients who did not recover after treatment (p = 0.02); and more frequent clinical features of fever (p <0.01), pleural effusion (p = 0.03), high white blood cell count (p <0.01) and C-reactive protein (p <0.01), and low level of albumin (p <0.01). Multivariate analysis adjusted by immunosuppressive drug use indicated significant differences of fever (p <0.01), high white blood cell count (p = 0.03), C-reactive protein (p = 0.01) and low level of albumin (p <0.01) in patients with eGFR <45 mL/min/1.73m 2 .

Conclusion
Severe CKD is associated with poor clinical characteristics and outcomes in patients with non-HIV pulmonary cryptococcosis.

Background
Cryptococcosis is an uncommon infectious disease caused by Cryptococcus neoformans and Cryptococcus gattii (1,2). The fungus mainly infects the lungs and central nervous system, but it can less frequently affect other organs, including the eyes, prostate, skin, and bone, in both immunocompetent and immunocompromised patients (3)(4)(5). Occasionally, cryptococcus can disseminate to several organs and lead to mortality, depending on the host immunity (6)(7)(8).
Pulmonary cryptococcosis is important, because the respiratory tract is the most common portal of entry (9,10). Several studies have reported that the clinical manifestations, including symptoms, laboratory data, radiologic findings, dissemination, and outcome, of pulmonary cryptococcosis were different in patients with immunocompromised comorbidities, such as human immunodeficiency virus (HIV) infection, diabetes mellitus, malignancy, organ transplantation, immunosuppressive treatment use, and chronic kidney disease (CKD) (5,(11)(12)(13)(14). CKD is one of the essential health conditions and is defined by an estimated glomerular filtration rate (eGFR) of < 60 mL/min/1.73 m 2 with positive findings of urinary protein that persists for 3 months (15,16). A large cohort study identified that an of eGFR < 45 mL/min/1.73 m 2 was related with all-cause and cardiovascular mortality (17). There is increasing evidence that CKD is closely linked with the host immune systems (18) and the risk for infections (19). Some reports identified that severity of CKD was involved with the clinical characteristics of pulmonary cryptococcosis (20,21); however the clinical features have not been fully assessed.
The purpose of this study is to clarify clinical characteristics of severe CKD in patients with pulmonary cryptococcosis. We investigated 56 patients with non-HIV pulmonary cryptococcosis and compared the clinical manifestations between 42 patients with eGFR > 45 mL/min/1.73 m 2 and 14 patients with eGFR < 45 mL/min/1.73 m 2 with positive findings of urinary protein. We identified that the symptoms, laboratory findings, radiologic patterns, and outcome, including dissemination, were different between the 2 groups and were worse in patients with pulmonary cryptococcosis and severe CKD.
These results may practically contribute to the clinical risk evaluation for pulmonary cryptococcosis.

Patients and setting
We retrospectively evaluated 56 patients diagnosed as pulmonary cryptococcosis without HIV infection at Saga University Hospital between 2005 and 2018. This study was approved by the ethics committee of Saga University Hospital (approval number: 2019-09-06, approval date: Nov 25, 2019) and was performed in accordance with the 1964 Declaration of Helsinki.
The assessment of pulmonary cryptococcosis was made by 1) clinical diagnosis, based on serum anticryptococcal antigen and chest radiologic abnormalities; 2) histologic diagnosis, based on the presence of cryptococcal pathogen on Grocott's staining of lung histologic samples and chest radiologic abnormalities; and 3) pathogenic diagnosis, based on the detection of cryptococcus species on airway, blood, or cerebrospinal fluid culture and chest radiologic abnormalities. All of the species detected from the cultured samples were C. neoformans. Disseminated cryptococcosis was defined as isolation of C. neoformans from blood, sterile body fluid, or any extrapulmonary site (8). Upon the diagnosis of pulmonary cryptococcosis, the clinical manifestations, including comorbidities, symptoms, laboratory data, and radiologic findings, were collected from the medical records and eGFR was calculated by formula as followed; 194 x Serum creatinine − 1.094 x Age − 0.287 x 0.739 (if female) (22). All patients with eGFR < 45 mL/min/1.73 m 2 were verified for the persistence of the same renal function for more than 3 months with positive findings of urinary protein, according to the CKD guidelines (15,17).
To address the clinical impact of severe CKD on pulmonary cryptococcosis, we divided 56 patients with pulmonary cryptococcosis into those with eGFR > 45 mL/min/1.73 m 2 (preserved eGFR) and those with eGFR < 45 mL/min/1.73 m 2 and positive findings of urinary protein (declined eGFR). The cutoff of 45 mL/min/1.73 m 2 for eGFR was set, based on a previous report that identified a relationship between mortality and eGFR < 45 mL/min/1.73 m 2 (17). Treatment, including the intake of antifungal drugs or surgery, was based on the physician's judgment. The outcome of non-recovery from pulmonary cryptococcosis after antifungal drug treatment for 3 months was defined as death or worsening radiologic and clinical findings.

Comorbidities
The predisposing factors, including pulmonary diseases, diabetes mellitus, connective tissue diseases, malignancy, immunosuppressive drug use, and hemodialysis, were collected from the medical records. There were no patients who received organ transplantation.

Statistical analysis
The clinical data were analyzed by Student's t-test for continuous variables or chi-square test for categorical variables. The present study found that immunosuppressive drug was used more often by patients with declined eGFR than by those with preserved eGFR. Because this might affect the current results, we performed multivariate analysis for the variables, including fever, white blood cell count, albumin, and C-reactive protein (CRP), which were significantly different between patients with preserved eGFR and those with declined eGFR in the univariate analysis (data not shown in tables).
Disseminated cryptococcosis, pleural effusion, and recovery after treatment were not assessed because of the small sample size. The comparative results were adjusted by the predisposing variable of immunosuppressive drug use. For multivariate analyses, logistic regression analysis for categorical variables and multiple linear regression analysis for continuous variables were performed.
Quantitative data were presented as mean ± standard deviation (SD), and odds ratio or coefficient β value were calculated. The two-tailed significance level was set at p < 0.05. Statistical analysis was performed with JMP Pro version 14.2.0 software (SAS Institute Inc., Cary, NC, USA).

Clinical characteristics and comorbidities in patients with pulmonary cryptococcosis
There were 42 patients with preserved eGFR and 14 patients with declined eGFR. Compared with the group with preserved eGFR, the group with declined eGFR had similar age, sex, and body mass index; tended to have higher number of patients with pathogenic diagnosis; had significantly higher rate of disseminated pulmonary cryptococcosis; similar comorbidities of pulmonary diseases, diabetes mellitus, connective tissue diseases, and malignancy; and more frequently used immunosuppressive  Comparison of the radiologic findings on HRCT in patients with pulmonary cryptococcosis According to previous reports on the different distribution and patterns of radiologic findings in pulmonary cryptococcosis, depending on immune status (12,23), we evaluated and compared the area and features of pulmonary abnormalities between patients with preserved eGFR and those with declined eGFR. Compared with the group with preserved eGFR, the group with declined eGFR had lower number of patients whose pulmonary abnormalities were limited to 1 lobe (p = 0.06) and were distributed in only a unilateral lung field (p = 0.07); similar patterns of single nodule, multiple nodules, masses, cavitation, consolidation, and ground glass attenuation; and significantly higher number of patients with pleural effusion (p = 0.03) ( Table 3). showed that the rate of recovery after treatment was significantly higher in patients with preserved eGFR than in those with declined eGFR (92% vs. 63.6%, p = 0.02) ( Table 4). immunosuppressive drug use, were associated with clinical characteristics (5,11,12). The current study found that immunosuppressive drug was used more often by patients with declined eGFR than by those with preserved eGFR (Table 1). Because this might affect the current results, we performed multivariate analysis for the variables which were significantly different between patients with preserved eGFR and those with declined eGFR. Disseminated cryptococcosis, pleural effusion, and recovery after treatment were not assessed because of the small sample size. On multivariate analysis, fever, white blood cell count, albumin, and CRP remained significantly different between patients with preserved eGFR and those with declined eGFR, even after adjustment (Table 5). Fever, white blood cell count, albumin and CRP which were significantly different between patients with higher eGFR and those with lower eGFR, and the comparative results were adjusted by predisposing variable of immunosuppressive drug use. eGFR; estimated glomerular filtration rate, CRP; C reactive protein, OR; odds ratio, β; standardized β value,

Discussion
In the present study, we analyzed 56 patients with non-HIV pulmonary cryptococcosis and evaluated the clinical characteristics depending on the CKD severity. We identified that the rates of disseminated cryptococcosis and non-recovery after treatment were significantly higher in patients with declined eGFR than in those with preserved eGFR. For the clinical features, fever, pleural effusion, high white blood cell count and CRP, and low level of albumin were more frequently seen in patients with declined eGFR than in those with preserved eGFR. To our best knowledge, this was the first report to clarify the clinical manifestations of severe CKD in patients with non-HIV pulmonary cryptococcosis.
CKD is one of the risk factors for pulmonary cryptococcosis; this statement is supported by several individual cases of severe clinical manifestations, such as dissemination and mortality, in chronic renal failure, especially when under dialysis (14,20). Pyrgos V et al reported that patients hospitalized for cryptococcus meningitis had significantly more frequent comorbidities of acute (28.5%) and chronic renal failure (14.3%), compared with those in all hospitalized patients (24).
Moreover, Hung MS et al identified that fever and pleural effusion were significantly more frequent in disseminated pulmonary cryptococcosis than in localized pulmonary cryptococcosis (8). Similarly, our findings showed higher rates of disseminated cryptococcosis and non-recovery after treatment in severe CKD patients with pulmonary cryptococcosis complicated by fever and pleural effusion.
The mechanisms of the association between CKD severity and the risk for pulmonary cryptococcosis remain unclear. However, some possible mechanisms, particularly the effect of the T cell response on the risk for pulmonary cryptococcosis and the pathophysiology of CKD, had been reported. HIV, which is characterized by a decline in CD4 + T cells, is one of the major causes of cryptococcosis (25).
Moreover, the clinical characteristics and outcome of pulmonary cryptococcosis in patients with immunocompromising conditions, such as underlying malignancy, immunosuppressive drug use, and diabetes mellitus, were reported to be different from those in immunocompetent patients (12,13,23). Likewise, CKD has been associated with inactivation of the T cell response and induction of T cell apoptosis (26,27), which causes immune dysfunction and increases the risk for infection (18,19).
Notably, host response to cryptococcal infection involves helper T cell response with production of cytokines, including tumor necrosis factor, interferon-ɤ, and interleukin-2 (28,29). According to these data, we considered that the immune dysfunction in severe CKD might have affected the clinical characteristics and outcomes of patients with pulmonary cryptococcosis.
The clinical characteristics, including symptoms, laboratory abnormalities, and radiologic features, in pulmonary cryptococcosis are variable (30). Consistent with our results, the absence of symptoms was reported to be relatively frequent in immunocompetent patients, whereas the pulmonary cryptococcosis-associated symptoms, especially fever and chest pain, were markedly seen in immunocompromised host (12,31). The radiologic patterns and distribution in pulmonary cryptococcosis have been closely related with host immunity. Nodules have been more frequently observed in immunocompetent patients, whereas pleural effusion, cavitation, and consolidation in a large lung area have been markedly observed in immunocompromised patients (31)(32)(33)(34). Our results of more frequent pulmonary CT abnormalities that were limited to 1 lobe and in a unilateral lung field in patients with preserved eGFR than in those with declined eGFR supported these previous data and the involvement of immunodeficiency from CKD. In addition, we clarified that high white blood cell count and CRP and low albumin might be biomarkers for risk evaluation in patients with pulmonary cryptococcosis and severe CKD.
There were 3 limitations in the present study. First, we used 45 mL/min/1.73 m 2 as the cutoff between preserved and declined eGFR, based on the results of a previous study (17). However, CKD is defined as eGFR < 60 mL/min/1.73 m 2 (15), and patients with mild CKD severity were included in the group with preserved eGFR; this might have influenced the results of this study. Second, treatment including the intake of antifungal drugs or surgery was elected depending on the physician's judgment, which might affect to the clinical outcomes. Third, the present study was performed on a small number of patients at a single hospital with limited ethnic diversity. To confirm the validity of our results, multicenter prospective studies with larger number of patients should be performed.

Conclusions
Compared with preserved eGFR, declined eGFR was associated with significantly higher rates of disseminated cryptococcosis and non-recovery after treatment and more frequent clinical features of fever, pleural effusion, high white blood cell count and CRP, and low level of albumin. These results may practically contribute to the clinical risk evaluation of patients with pulmonary cryptococcosis.

Ethics approval and consent to paticipate
This study was approved by the ethics committee of Saga University Hospital (approval number: 2019-09-06, approval date: Nov 25, 2019) and was performed in accordance with the 1964 Declaration of Helsinki.

Consent for publications
Not applicable

Availability of data and materials
The datasets used and analyzed during the current study are available from the corresponding author on reasonable request.

Competing interests
The authors declare that they have no competing interests.

Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Author Contributions
HT, TH, KT, and NA conceived the project. HT, KT, HS and NA designed the clinical research and interpreted the data. RT and AT advised for statistical analysis. HT and KT prepared the manuscript with input from all other authors. KT, SK and NA performed final check of manuscript.