Use of Self-expanding Metallic Airway Stents in Tracheobronchomalacia

To the Editor: Airway stents have evolved in design, material, and applications. Predominantly used in the treatment of central airway obstruction, the 2 types of stents, silicone and metal (fully covered, partially covered, and uncovered), offer different advantages and disadvantages. Silicone stents suffer from mucus plugging, high rate of migration, and inability to conform to tortuous airways, and require rigid bronchoscopy for deployment. However, they are less expensive and are relatively easy to remove. Self-expanding metallic airway stents (SEMAS) have less mucus plugging, less incidence of migration, better conform to tortuous airways, and can be easily deployed using flexible or rigid bronchoscopy. However, when left for a prolonged period of time, SEMAS are significantly harder to remove, with increased potential for complications.1,2 Because of these considerations, FDA has recommended that silicone stents be used as first line in the treatment of benign airway disease, and SEMAS as the last resort or for palliation of malignant airway obstruction.3 We have the privilege of treating a large number of patients with tracheobronchomalacia (TBM) at our institution. TBM, a disease characterized by weakness of the central airways, presents as expiratory airway collapse and is associated with cough, dyspnea, inability to clear secretions, and recurrent infections. Treatment is considered only after patients remain symptomatic despite optimal management of their underlying diseases. The mainstay treatment for TBM is surgical.4 Evaluation for surgery requires a stent trial5; those with improved symptoms are considered surgical candidates, and those without receive medical management. Although studies in patients with TBM have shown a high rate of complications from silicone stents,5 there is limited information on alternatives, especially on the safety and efficacy of SEMAS when used for a short period of time in this patient population. Interestingly, there is some juxtaposition between the characteristics of TBM and the problems with silicone stents: a high rate of stent migration with weak airways, inability to clear secretions with stent-mediated reduction in mucociliary clearance, and excessive granulation tissue formation at the distal end due to increased friction of the stent and the airway wall. However, SEMAS are associated with less migration, maintain mucociliary clearance, and are suitable for small and collapsible airways, making SEMAS theoretically a better option for short-term stent trial in patients with TBM. Of special interest are patients who have TBM with cough as the predominant symptom, in whom we have observed a variable response to the stent trial when Y-silicone stents are used: cough will improve in 33% of patients, 33% will have no change, and 33% experience significant worsening (A.M., E.F., unpublished data). The exact mechanism of cough in TBM during a stent trial is unclear. This poses an interesting question of whether restoring airway patency using SEMAS may be more advantageous compared with using a Y-silicone stent, which may initiate cough reflex by physical stimulation of the highly sensitive carina.6 Finally, recent reports indicate that metal stents can be removed safely, especially if removed before 6 to 8 weeks.7 After a careful multidisciplinary evaluation, we offer a SEMAS trial to patients with severe and symptomatic TBM who have cough as the primary symptom or had undergone a previous equivocal silicone stent trial. Three patients with a history of equivocal silicone stent trial and severe symptomatic TBM (1 patient had severe tracheal collapse, and the other 2 had bilateral collapse in both main stem bronchi) recently underwent a SEMAS trial. To objectively evaluate symptom improvement, we applied a previously validated Leicester Cough Questionnaire (LCQ) and Medical Research Council (MRC) dyspnea score before, during, and after the stent trial. Mean baseline scores were LCQ=32 and MRC=3 (LCQ ranges from 19 to 133, with lower scores indicating increasing cough severity, and the MRC score ranges from 1 to 4, with higher scores indicating more severe dyspnea). All demonstrated significant improvement in cough and dyspnea scores during the stent trial (median LCQ=102, MRC=1) and had no stent-related complications. Stents were removed after 5 days and symptom scores went back to baseline (median LCQ=32, MRC=3). There was minimal granulation tissue and no difficulties during the removal procedure in all cases (Fig. 1). Subsequently, all patients successfully underwent surgical tracheoplasty.FIGURE 1: A, Bronchoscopic image of uncovered SEMAS in the trachea one week after implantation. B, Airway mucosa immediately after SEMAS removal.We believe that SEMAS are safe and effective in alleviating symptoms and in identifying patients with TBM who may benefit from surgical airway stabilization. If the SEMAS trial is limited to <5 days and is performed by experienced operators, the results are excellent, especially in patients who present with cough as the predominant symptom or have undergone an equivocal silicone stent trial. Prospective, randomized, blinded studies are needed to validate these observations. It is important to emphasize that, if SEMAS are left in place for prolonged periods of time, they may cause more granulation, greater risk of stent fracture, will become harder to remove, and will increase health care utilization.1 Our protocol lies within the FDA recommendation of the use of SEMAS after thoroughly exploring other options, and is performed by an experienced person in metallic stent removal. Sebastian Ochoa, MD* George Z. Cheng, MD, PhD*,† Erik Folch, MD, MSc, MPH* Adnan Majid, MD, FCCP* *Division of Thoracic Surgery and Interventional Pulmonology, Beth Israel Deaconess Medical Center †Division of Pulmonary and Critical Care, Massachusetts General Hospital, Harvard Medical School, Boston, MA