Isolated Pulmonary Cryptococcosis Confused with Lung Tumor 5 Years After Kidney Transplantation: A Case Report

Background. In transplant recipients, due to the use of immunosuppressive therapy, it is occasionally difficult to distinguish between an infection and malignancy, especially in the case of a lung lesion. Here, we report a case of isolated pulmonary cryptococcosis after kidney transplantation that was difficult to distinguish from a lung tumor. Case report. A 52-year-old man underwent a kidney transplant from his mother when he was 44 years old. Immunosuppression was maintained with tacrolimus, methylprednisolone, and mycophenolate mofetil. His post-transplant course was uneventful and serum creatinine levels were maintained. Five years post-transplantation, a non-contrast computed tomography (CT) examination revealed a nodule measuring 3 mm in diameter in the middle lobe of the right lung. The nodule gradually increased to 12 mm in 2 years. Positron emission tomography/CT examination showed a maximum standardized uptake value of 0.5 for the nodule. Biochemical examination revealed no elevation in total leucocyte count and C-reactive protein levels. However, tumor markers were elevated: serum carcinoembryonic antigen, 5.9 ng/mL; pro-gastrin-releasing peptide, 84.6 pg/mL. Furthermore, the serum cryptococcus antigen was negative. Therefore, thoracoscopic partial lung resection was performed. Pathologically, a number of spherical fungi from the necrotic substance of the tumor were confirmed positive by periodic acid-Schiff and Grocott-Gomori staining. The patient was therefore diagnosed with pulmonary cryptococcosis. Two years later, the patient is alive and has shown no evidence of recurrence. Conclusions. In lung nodules after kidney transplantation, even if serum cryptococcus antigen is not identified, it is necessary to keep in mind the possibility of pulmonary cryptococcosis.