pulmonary infection mimicking steroid-refractory radiation pneumonitis during corticosteroid taper: a case report.

[BACKGROUND] Radiation pneumonitis (RP) is a common complication after thoracic radiotherapy, and corticosteroids are the mainstay of treatment. However, prolonged or high-dose steroid therapy predisposes patients to opportunistic infections that may closely mimic steroid-refractory RP, especially during the tapering phase. Distinguishing radiation-induced lung injury from superimposed fungal pneumonia in this setting is a major clinical challenge.

[CASE DISCRIPTION] We report a 55-year-old man with non-small cell lung cancer (NSCLC) who developed RP after surgery and adjuvant thoracic radiotherapy. His respiratory symptoms initially improved with high-dose intravenous methylprednisolone and antibacterial therapy. Early during steroid tapering, however, he experienced recurrent fever, worsening dyspnea, and new bilateral ground-glass opacities on chest computed tomography (CT) extending beyond the original radiation field. These findings raised concern for either RP flare or opportunistic infection. Bronchoscopy revealed congested bronchial mucosa with purulent secretions, and bronchoalveolar lavage (BAL) microscopy identified fungal spores. species grew in BAL culture, serum (1,3)-β-D-glucan (BDG) exceeded 600 pg/mL, and galactomannan (GM) values fluctuated around the diagnostic cut-off (peak, 1.07 ng/mL). Integrating the clinical, radiologic, and microbiologic data, RP complicated by pulmonary infection was diagnosed. Oral fluconazole therapy was initiated, trimethoprim-sulfamethoxazole (TMP-SMX) was given for empirical coverage, and the corticosteroid dose was deliberately tapered rather than escalated. The patient's symptoms, oxygenation, and inflammatory markers improved within 2 weeks, and follow-up imaging at 6 weeks showed marked absorption of pulmonary opacities.

[CONCLUSIONS] This case illustrates that pulmonary infection can present as apparent steroid-refractory RP during corticosteroid taper. In RP patients whose respiratory status deteriorates under steroid therapy, particularly when CT abnormalities extend beyond the radiation field, clinicians should maintain a high index of suspicion for opportunistic fungal infection. Early bronchoscopy with BAL, careful interpretation of fungal biomarkers, timely initiation of targeted antifungal therapy, and judicious tapering-rather than automatic escalation-of corticosteroids are crucial to reversing clinical deterioration and improving short-term outcomes.