In response to Late complications of nickel‐titanium alloy stent in tracheal stenosis

Dr. Glenn Knox raised an interesting point, that nickel allergy may have contributed to or exacerbated granulation formation and tracheal stenosis in the patients with nickel-titanium alloy stent placement in our study. To determine this possibility, we reviewed the medical records of 10 patients with laryngotracheal stenosis due to the insertion of nickel-titanium alloy stents. None of them had a history of nickel allergy, although one patient had a history of contact dermatitis. As to eosinophilic infiltration in the excised granulation tissues, only one patient was examined from a biopsy of the original reconstructive tissue after complex nitinol alloy web placement and myocutaneous flap for the laryngotracheal lumen reconstruction, which caused laryngotracheal restenosis 4 years later. The pathologic examination showed that inflammatory lymphocytes (90.4%), neutrophils (9.0%), and eosinophils (0.6%) infiltrated in the mucosal and submucosal tissues (data not shown). In our previous animal experiments, the titanium alloy stents (self-expanding metallic stents) were implanted in the trachea of rabbits for a period of 3 to 6 months. All of the rabbits were observed having increased thickness of the tracheal membranes via endoscopy and scanning electron microscopy. The blood and granulation tissues were collected for histopathologic examination. Although increased infiltration of inflammatory lymphocytes, macrophages, and neutrophils was seen in the mucosal, submucosal, and muscular tissues 3 months after stent implantation, eosinophils were rarely seen in the samples. Inflammatory leukocytes were rarely seen 6 months after stent implantation (data not shown). The findings from our study are consistent with what were shown in other reports, in which patients were implanted with stents for the treatment of cardiac and intracranial atherosclerotic diseases. Our study does not support the idea that nickel allergy contributed to granulation formation and tracheal stenosis. However, largescale studies need to be done to further confirm this. We are grateful for Dr. Knox’s interest and great suggestions regarding our study. We will try to compare goldor platinum-plated nitinol implants with nickeltitanium alloy stents in our patients and perform pathological examinations from patients’ biopsies so that we can reach a final conclusion.