Brief Summary

The goal of this clinical trial is to determine whether an initial diagnostic approach using ultrasound elastography-guided pleural biopsy (UEPB) is non-inferior to immediate medical thoracoscopic pleural biopsy in terms of diagnostic yield for obtaining a definitive histopathological diagnosis in patients with exudative pleural effusion of unclear etiology.

The main questions it aims to answer are:

Is the step-up strategy (UEPB first, reserving thoracoscopy for non-diagnostic cases) non-inferior to immediate medical thoracoscopy in diagnostic yield?

Does the step-up strategy provide advantages in safety, patient tolerance, hospital stay, and cost-effectiveness compared to immediate thoracoscopy?

Researchers will compare a step-up strategy (initial UEPB, followed by medical thoracoscopy if UEPB is non-diagnostic) versus immediate medical thoracoscopic pleural biopsy to see if the step-up approach achieves comparable diagnostic accuracy while potentially reducing procedure-related burden and healthcare resource use.

Participants will:

Be randomly assigned in a 1:1 ratio to either the step-up strategy arm or the immediate medical thoracoscopy arm.

If assigned to the step-up arm: undergo UEPB under local anesthesia; if the biopsy is non-diagnostic, proceed to semi-rigid medical thoracoscopy.

If assigned to the immediate thoracoscopy arm: undergo semi-rigid medical thoracoscopic pleural biopsy as the initial and sole diagnostic procedure.

Provide tissue samples for histopathological, immunohistochemical, and molecular analyses as clinically indicated.

Complete short-term follow-up at 7 days post-procedure (by telephone or clinic visit) to monitor adverse events and symptom recovery.

If initially diagnosed with non-specific benign disease or remain undiagnosed, complete a long-term follow-up at 12 months to establish a final diagnosis.

Inclusion Criteria:

1. Age ≥18 years;
2. Patients with exudative pleural effusion of unknown origin;
3. Patients with negative pleural fluid cytology results;
4. Patients who had not undergone pleural biopsy before enrolment.

Exclusion Criteria:

1. Significantly bleeding risk, including uncorrectable coagulopathy (such as INR >1.5, platelet count <50×109 /L) or the need for ongoing anticoagulant/antiplatelet therapy that cannot be safely paused;
2. Hemodynamic instability;
3. Refractory hypoxemia despite supplemental oxygen;
4. Any severe concurrent illness or cardiopulmonary compromise that, in the investigator's judgment, makes either procedural sedation (for thoracoscopy) or a bedside biopsy (for UEPB) unsafe;
5. Pleural effusion conclusively identified as a transudate;
6. Pregnancy or lactation;
7. Any condition that, in the investigator's judgment, would compromise protocol compliance or follow-up.