Is trans-laryngeal ultrasound (TLUS) an accurate and acceptable tool in the assessment of inducible laryngeal obstruction? A protocol for the ILOTUS: A cross-sectional, two-stage feasibility study

BACKGROUND: Inducible laryngeal obstruction (ILO) describes an inappropriate narrowing of the larynx during breathing in. ILO can lead to several respiratory symptoms and be misidentified and treated as asthma, with associated patient morbidity and healthcare cost. ILO is also known as vocal cord dysfunction, or paradoxical vocal fold movement. The current reference assessment tool for diagnosing ILO is a video-laryngoscopy. However, timely access to specialist diagnostic laryngoscopy services may be challenging, and laryngoscopy may be poorly tolerated. AIMS: The aim of this cross-sectional, two-stage feasibility study is to determine whether abnormal vocal fold movements associated with ILO can be adequately visualised using trans-laryngeal ultrasound (TLUS) namely, the ILOTUS study: (ILO assessment via trans- laryngeal ultrasound). The second aim is to compare TLUS with a reference standard diagnostic tool to ascertain whether it may serve as a less invasive screening tool to assess ILO. Participants’ opinions about the acceptability of TLUS will also be gathered and compared with responses to a validated symptom score questionnaire. METHODS: In stage one, healthy volunteers (n = 30) will undergo TLUS to assess whether the vocal folds can be visualised,and whether narrowing of the vocal folds can be seen when they mimic ILO. Stage 2 will be conducted with a patient population(n = 30) referred to a tertiary airways service for breathlessness assessment. Participants in stage 2 will undergo the reference standard laryngoscopy as well as simultaneous TLUS. The level of agreement between TLUS and laryngoscopy will be evaluated, as well as comparison of symptom scores. DISCUSSION: This study will help inform future studies of the utility of TLUS in the assessment of ILO. This will be valuable for understanding whether TLUS could be offered as a non-invasive option for patients in the assessment of ILO if they are not able to tolerate or access laryngoscopy diagnostic services. It is not intended that TLUS will replace the current reference standard of video-laryngoscopy but may have potential as an early screening tool if found to be non-inferior.