Emerging diagnostic techniques

The current gold standard assessment tool for the diagnosis of ILO/VCD is laryngoscopy.

The patient journey to a confirmed diagnosis of ILO/VCD, can be lengthy and challenging as centres that specialise in the assessment of ILO/VCD are few. Even within these centres, there may be few skilled personnel and limited access to the facilities/equipment to undertake laryngoscopy when needed.  Additionally, some patients may not be able to tolerate the procedure.  As a result, there is interest in looking at alternative and additional methods of diagnosis for ILO/VCD to expedite diagnosis and appropriate treatment.  Several alternatives or additions to laryngoscopy have been proposed in able to offer patients a choice if they cannot tolerate, do not want or cannot access laryngoscopy.

Recent developments in diagnostic imaging have shaped alternative diagnostic options, particularly with advancements in dynamic computerised tomography (CT). This new technology yields superior spatial and temporal resolution, allowing not only visualisation of anatomical features, but also detection of movement and function of tissue and organs. Initial studies of dynamic CT larynx have demonstrated accurate imaging of vocal cord movement during respiration, providing quantification of the degree of vocal cord narrowing in graphic format. Radiation exposure is small (0.8-1.0 milliSievert) due to high soft tissue-air interfaces. 

Dynamic CT larynx provides accurate reconstructed images of the larynx comparable to laryngoscopy. Figure demonstrates CT coronal reconstruction during inspiration (a,b) and  laryngoscopy images in the same patient (c,d). Matched images demonstrate normal function (a,c) and the presence of VCD/ILO characterised by inspiratory closure of the vocal cords following a period of hyperventilation (b,d).

In an important study patients were assessed by laryngoscopy and dynamic CT larynx, either contemporaneously, or on separate days. The findings of CT larynx were then analysed for accuracy again laryngoscopy as the gold standard. The imaging modality was shown to possess high specificity for diagnosis of ILO/VCD (up to 90%) as well as high negative predictive value (also up to 90%). This recently published data demonstrates potential for dynamic CT larynx to be utilized in the clinical setting as an initial screening tool to reduce demand for laryngoscopy, particularly in centres lacking access to laryngoscopy. A further benefit is that conditions causing complex breathlessness, such as excessive central airway collapse, can also be diagnosed.  In patients with co-morbidities such as sino-nasal and pulmonary disease there may be a role to expand the dynamic CT larynx to include the paranasal sinuses and chest in a ‘triple airway CT’ (TACT). Further studies are needed to evaluate the role of TACT as a useful diagnostic approach in patients with suspected ILO/VCD and complex upper, middle and lower airway disease.

Use of an algorithm based on normal vocal cord movement generates a curve denoting vocal cord aperture over a breath cycle. A predicted mean normal curve with a second curve depicting the lower limit of normal (LLN; stippled lines) were derived from healthy individuals.  Solid lines depict normal laryngeal movement (left panel) and ILO/VCD (right panel). Dynamic CT larynx provides accurate quantification of the severity of ILO/VCD with high specificity (>90%) and moderate sensitivity (~60%).

Transcutaneous ultrasound assessment of the vocal folds (TLUS) is an emerging methodology with a developing evidence base for use in the assessment of swallowing and laryngeal function.  A systematic rapid review concluded sensitivity and specificity of ~ 60% and ~50%, respectively for detection of ILO/VCD when compared to laryngoscopy.  

TLUS assessment for diagnosis of ILO/VCD is a potential novel application. However, there is limited research on its use in this setting.  Ultrasound is less invasive than laryngoscopy and may be more acceptable and accessible to patients.  However, it is more difficult to interpret than laryngoscopy, and may not be as accurate.  Factors such as gender, age, height and BMI may affect image acquisition. Feasibility studies are being conducted to investigate if ultrasound could be a useful and acceptable early screening tool to visualise abnormal vocal fold movements seen in ILO/VCD that may help us understand if TLUS has utility to aid earlier identification of ILO/VCD. 

There may be additional benefits of TLUS, including:

• Reduced waiting time for the procedure (compared to laryngoscopy)
• Improved acceptability
• Fewer associated procedure costs
• Accessibility (can be accessed in a clinic setting)
• Option for patients who cannot have a laryngoscopy, due to medical considerations, (such as severe sinus disease/sensitivity/injury, following sino-nasal or base of skull surgery, previous vaso-vagal episode or epistaxis).

During TLUS, a high-frequency linear probe is placed on the thyroid cartilage to visualise the vocal folds (see image). Observations of any changes in the vocal fold positions when breathing in compared to breathing out at rest, and after challenges are presented (deep breathing, coughing, speaking at volume, and scent triggers if necessary).  Any kinematic impairments during the inspiratory or expiratory phase are noted.

TLUS may have potential to be a useful tool in an early screening assessment of ILO in conjunction with other established diagnostic methods to help make a definitive diagnosis. It allows the clinician to non-invasively visualise the vocal folds and structures of the larynx in real-time, and in different situations, due to its portability.

However, more research is needed to confirm optimal image acquisition, accuracy, effectiveness, reliability and acceptability.  The current literature does not support its use as a diagnostic tool in isolation.

Technology to improve access to laryngoscopy images has been employed by way of mobile phone apps and adapters that enable linking laryngoscopes  directly with mobile phones. (Endoscope-i Ltd, Birmingham, UK.).  This was found of particular benefit during the COVID pandemic-era.  The method uses a mobile phone to record laryngoscopy with later play back and review.  It obviates the need for traditional bulky and complex imaging and recording equipment.