Two Case Reports on Pleural Effusion with Rare Causes: Yellow Nail Syndrome and Chylothorax

Objective: The widespread adoption of medical thoracoscopy across various hospital settings has significantly improved the diagnostic rate for exudative pleural effusion. However, challenges persist in identifying rare etiologies, such as disorders of lymphatic circulation. This article aims to examine the diagnostic approach for these pleural effusions to enhance clinical diagnostic and treatment capabilities. Methods: We retrospectively analyzed the clinical data of two patients with rare pleural effusions admitted to our hospital, in whom the etiology remained unclear following conventional medical thoracoscopy. A review of the relevant literature was also conducted. Results: Both patients presented with exudative pleural effusion; however, medical thoracoscopy and pleural biopsy revealed chronic inflammation. The final diagnoses for the two patients were Yellow Nail Syndrome (YNS) and chylous pleural effusion, respectively. The literature review indicates that the etiology of such conditions is often associated with dysfunction of the lymphatic system, and conventional pleural biopsy has a low positive rate, making lymphangiography a more effective diagnostic method. Conclusion: For pleural effusions with an unclear diagnosis following medical thoracoscopy, it is crucial to expand diagnostic considerations. If the etiology remains undetermined after comprehensive routine pleural fluid analysis and pleural biopsy, rare diseases related to lymphatic circulation disorders should be contemplated. Thorough history-taking, systematic physical examination, and targeted auxiliary tests, such as lymphangiography, are essential for achieving a definitive diagnosis.