BACKGROUND: Spontaneous resolution of Pneumocystis jirovecii pneumonia has rarely been reported.

CASE REPORT: A 59-year-old man presented to our hospital because of pyrexia (38°C) and shaking chills for 2 days. He had a history of right nephrectomy due to renal cell carcinoma and left upper lobectomy for lung metastasis in the last 1.5 years. Two months previously, he was treated with oral prednisolone (20 mg/day) plus the intravenous mTOR inhibitor, temsirolimus (25 mg/week), for brain metastasis. On radiological examination, thoracic computed tomography showed diffuse ground glass opacities spreading in bilateral middle to lower lung fields. Although transbronchial biopsy specimens and bronchoalveolar lavage fluid demonstrated the presence of accumulation of black-colored Pneumocystis jirovecii cysts in the lung, his chief complaints and radiological abnormalities disappeared completely with no treatment. This case demonstrates a unique clinical presentation of Pneumocystis jirovecii pneumonia, in that spontaneous resolution was noted on clinical and sequential radiological evaluations.

CONCLUSIONS: Increasing numbers of cytotoxic drugs and biological therapies have emerged, and changes in the immune status due to underlying diseases or administration of immunosuppressive drugs might affect the inflammatory process of Pneumocystis jirovecii pneumonia, as in the present case.

Keywords: Bronchoscopy, Biopsy, Carcinoma, Renal Cell - diagnosis, Diagnosis, Differential, Immunocompromised Host, Kidney Neoplasms - diagnosis, Pneumocystis jirovecii - isolation & purification, Pneumonia, Pneumocystis - microbiology, Remission, Spontaneous, Tomography, X-Ray Computed - methods