Rationale Interstitial lung diseases (ILDs) require accurate histological diagnosis when imaging is inconclusive, yet current techniques-surgical lung biopsy and transbronchial cryobiopsy-carry significant risks and lack real-time guidance. BPTE, widely used in oncology, provides ultrasound-guided sampling under local anesthesia with historically lower complication rates, but its value in ILD remains unproven. The TOUCANS study aims to generate safety and feasibility data to support its potential use as a less invasive diagnostic alternative.

Objectives The primary objective is to assess the safety of BPTE in ILD patients, focusing on major adverse events: death, pneumothorax requiring drainage, hemorrhage requiring intervention, and prolonged pleural drainage. Secondary objectives include evaluating all complications within two months, comparing BPTE histological quality with surgical biopsy, and assessing pain, dyspnea, analgesic use, healing, drainage duration, and hematoma on thoracoscopic imaging.

Materials and Methods Fifteen patients aged 18-75 with ILD requiring tissue diagnosis after multidisciplinary review will be included. Exclusion criteria cover coagulation disorders, severe comorbidities, long-term oxygen therapy, impaired lung function, obesity, pulmonary hypertension, anesthetic allergy, and vulnerable populations. BPTE will be performed 2-4 weeks before surgical biopsy, under local anesthesia and spontaneous ventilation, with CT- and ultrasound-guided targeting. One or two biopsies will be taken, followed by ultrasound and chest X-ray monitoring; discharge occurs after four hours if stable. Surgical thoracoscopic biopsy will then be carried out with standard postoperative care. Pain, dyspnea, healing, and imaging findings will be recorded, and histological samples will be reviewed blindly. Data will be captured in eCRFs according to GDPR/CNIL requirements.

Expected Outcomes TOUCANS will provide the first prospective evidence on BPTE for ILD. Demonstrating safety and adequate diagnostic yield could position BPTE as a minimally invasive, outpatient, ultrasound-guided alternative to surgical biopsy. This may shorten diagnostic pathways, reduce complications, and offer a viable option for patients unsuitable for surgery, ultimately improving early management and prognosis.

The TOUCANS study is a prospective, interventional, single-center protocol designed to evaluate the feasibility and safety of transthoracic ultrasound-guided lung biopsy (BPTE) for the histopathological assessment of patients with interstitial lung disease (ILD). Surgical lung biopsy (SLB) remains the reference diagnostic standard when high-resolution CT and multidisciplinary evaluation are inconclusive; however, SLB requires general anesthesia and thoracoscopy and is associated with non-negligible morbidity. Cryobiopsy offers a less invasive option but still relies on general anesthesia and does not provide real-time guidance during tissue acquisition. BPTE, routinely used in oncology, may provide a safer and more accessible alternative by combining real-time thoracic ultrasound guidance with local anesthesia and outpatient feasibility. Its use in ILD has been limited due to a lack of prospective safety and diagnostic performance data.

Scientific Background ILDs often involve peripheral and subpleural abnormalities that can be visualized using thoracic ultrasound. Real-time ultrasound allows operators to identify pleural irregularities, increased B-lines, or localized reductions in aeration that may correspond to accessible sampling sites. These features form the basis for selecting BPTE target zones. BPTE has shown low complication rates in other clinical contexts, including pneumothorax and hemorrhage, but its applicability to ILD requires systematic evaluation given the underlying fragility of this patient population.

Study Rationale By performing both BPTE and SLB in each participant, the study aims to document the safety profile of BPTE relative to the current gold standard and compare tissue quality. This within-subject design allows direct assessment of histological adequacy and potential concordance between techniques, while limiting inter-individual variability. The protocol also aims to document patient-reported outcomes such as pain and dyspnea and to characterize local tissue effects at the BPTE site during subsequent thoracoscopy.

Study Procedures After standard diagnostic workup and confirmation of biopsy indication by multidisciplinary discussion, participants undergo baseline clinical assessment and high-resolution CT imaging. BPTE is performed 2-4 weeks before SLB to ensure procedural independence and adequate healing time. Under local anesthesia and spontaneous ventilation, the operator identifies an appropriate intercostal window using thoracic ultrasound. A target region is selected based on pleural surface abnormalities or an increased number of B-lines. One or two core biopsies measuring at least 1 cm are obtained using a dedicated cutting needle during a brief apnea. Post-procedure monitoring includes lung ultrasound and chest radiography to detect pneumothorax. Patients are discharged after a four-hour observation period unless complications occur.

SLB is performed under general anesthesia via video-assisted thoracoscopy. The thoracic surgeon documents the BPTE site, enabling evaluation of hematoma or other local effects. Standard postoperative care includes pleural drainage and scheduled follow-up visits. Histological samples obtained through BPTE are stored and analyzed at the end of the follow-up period to ensure blinded comparison with surgical specimens.

Data Collection and Management Clinical assessments include evaluation of procedural tolerance, pain, dyspnea, and healing. Thoracoscopic imaging of the BPTE site provides additional information on local changes. All data are entered into electronic case report forms (eCRFs) with access restricted to authorized study personnel. Data management follows GDPR and CNIL requirements, with predefined monitoring procedures to ensure accuracy, completeness, and consistency.

Statistical Approach Given the exploratory nature of the study, the sample size of 15 participants is based on feasibility considerations. Analyses will primarily rely on descriptive statistics to summarize safety outcomes, histological adequacy, and patient-reported measures. No formal hypothesis testing is planned, but the dataset is expected to support the design of future multicenter studies.

Safety Oversight Adverse events and serious adverse events will be documented throughout the study period. Investigators are responsible for evaluating severity and causality and reporting events to the sponsor. An independent safety monitoring committee will review safety data periodically. Regulatory and ethical compliance includes approval from national authorities and ethics committees, informed consent procedures, and insurance coverage for participants.

Expected Contribution The TOUCANS study will provide the first prospective evidence on BPTE in ILD. The findings may clarify whether BPTE can serve as a safe and technically reliable method for obtaining diagnostic tissue in selected ILD patients, potentially reducing the need for surgical biopsy and improving access to histological diagnosis in those with contraindications to invasive procedures.

Inclusion Criteria

• Age 18-75 years
• Diagnosed with diffuse ILD
• Histological analysis required after standard diagnostic workup
• Biopsy indication validated by MDD
• Affiliated with French social security
• Written informed consent Exclusion Criteria
• Contraindication to SLB
• Coagulation disorders
• Significant comorbidities affecting safety
• Long-term oxygen therapy
• FVC <55%, DLCO <40%
• BMI >35 kg/m²
• Pulmonary hypertension (PAPS >40 mmHg)
• Allergy to anesthetics
• Protected populations (pregnant women, minors, legally protected adults)
• β-HCG test required for non-menopausal women

The datasets generated and/or analyzed during the current study will be made available from the corresponding author on reasonable request. The conditions for the transfer of all or part of the database will be decided by the study sponsor and will be the subject of a written contract.