A Case of Pneumocystis Pneumonia Caused by Long-Term Low-Dose Steroid Therapy

Pneumocystis pneumonia (PCP) is an opportunistic infection caused by Pneumocystis jirovecii. It typically occurs in patients with advanced HIV infection and severely reduced CD4+ T cell counts, but it is also seen in other immunocompromised hosts such as those receiving long-term corticosteroids, immunosuppressive agents, or chemotherapy. Common symptoms include progressive dyspnea, dry cough, and low-grade fever. In general, patients at risk for PCP who are receiving the equivalent of 20 mg/day or more of prednisolone for at least eight weeks are recommended to receive prophylactic trimethoprim-sulfamethoxazole (TMP-SMX) therapy. We report our experience of managing PCP in an 80-year-old man with a history of rheumatoid arthritis who had been receiving oral prednisolone 4 mg/day for 21 years. The patient was admitted to our hospital for rehabilitation due to disuse syndrome following surgery for aortic dissection. On hospital day one, the patient developed a fever. Oxygenation impairment was observed, prompting chest radiography and subsequent computed tomography (CT) imaging, which revealed reticular shadows and ground-glass opacities in both lung fields. These findings led to the suspicion of bacterial pneumonia and initiation of ceftriaxone therapy. By day four, his oxygen saturation dropped to 90% on room air, and laboratory tests showed a β-d-glucan level of 62.5 pg/ml. On day five, the antibiotic regimen was switched to meropenem, vancomycin, and TMP-SMX. Bronchoscopy was considered unsafe because of the patient's general condition, and sputum polymerase chain reaction (PCR) was performed instead, which was positive for Pneumocystis jirovecii. Based on the PCR results, clinical course, and imaging findings, a diagnosis of PCP was made. ST and atovaquone were administered for a total of three weeks, resulting in defervescence and significant improvement in oxygenation. Even low-dose corticosteroid therapy is associated with an increased risk of opportunistic infections, depending on the cumulative dose. Although our patient had been receiving only a low daily dose, the cumulative exposure indicated a high risk for infections such as PCP. In conclusion, our case experience suggests that in patients receiving long-term corticosteroid therapy, PCP and other opportunistic infections must be considered in the differential diagnosis of pneumonia, regardless of the daily corticosteroid dose received.