Abstract Introduction Pulmonary nodular lymphoid hyperplasia (PNLH) is a rare benign lymphoproliferative disorder characterized by a localized, non-clonal proliferation of lymphoid tissue forming a solitary pulmonary nodule. It must be distinguished from mucosa-associated lymphoid tissue (MALT) lymphoma. The lesion typically represents reactive lymphoid proliferation and is often discovered incidentally. Because of its radiologic similarity to malignancy, accurate diagnosis requires histopathologic confirmation and immunohistochemical profiling. Case Report A 54-year-old woman with a 14-year history of multiple sclerosis treated with fingolimod presented with persistent lymphopenia (∼350 cells/µL) but no respiratory symptoms. During MRI follow -up for her neurological condition, a pulmonary nodule was incidentally identified. Chest CT revealed a 17 mm spiculated nodule in the apical segment of the right upper lobe, without mediastinal or hilar lymphadenopathy (Figure 1a). The patient had no history of smoking and had no other risk factors for malignancy, although chronic immunosuppression increased susceptibility to lymphoproliferative and infectious disorders. A video-assisted wedge resection was performed. Histopathology showed peribronchiolar lymphoid proliferation with reactive germinal centers and scattered plasma cells (Figure 1b). Immunohistochemistry was positive for CD20+, with germinal centers expressing CD10+ and BCL6 but negative for BCL2. Follicular dendritic cells were positive for CD21+ and CD23+. These findings supported the diagnosis of pulmonary nodular lymphoid hyperplasia (PNLH). Discussion This case highlights the challenges of pulmonary nodules in immunocompromised patients receiving long-term immunomodulatory therapy. Clinical and imaging findings are often non-specific, making it challenging to differentiate reactive from malignant lesions. PNLH has no specific medical therapy; surgical resection is generally curative, and recurrence is rare. Conclusion This case shows that benign lymphoid proliferations can mimic malignancy radiologically and clinically. Recognition of pulmonary nodular lymphoid hyperplasia (PNLH) is essential to avoid misdiagnosis and inappropriate oncologic therapy. Beyond malignancy or infection, this entity should also be considered in immunomodulated patients presenting with solitary pulmonary nodules, as it often represents a diagnosis of exclusion. In such settings, surgical resection serves as a diagnostic procedure to achieve tissue confirmation and guide appropriate management This abstract is funded by: None
Brocato et al. (Fri,) studied this question.