Ultrasound to Detect Vocal Fold Movement in Neurological Disease

The availability of cheaper and more portable ultrasound (US) machines has resulted in the extension of the use of US beyond the radiology department into diverse clinical areas. In particular, the Covid-19 pandemic has intensified interest in US as an alternative tool to use within the Speech and Language Therapy (SLT) profession to assess swallowing and airway disorders as access to routine assessment tools such as fibreoptic endoscopic examination (FNE) was restricted to its due aerosol-generating properties (Bolton et al., 2020).

The use of US by allied health professionals, such as Speech and Language Therapists (SLTs), is driven by National Institute for Health and Care Excellence (NICE) guidance and government policy (The Royal College of Radiologists, 2017) whereby the range of applications and locations where US can be used makes it impractical to deliver this imaging using radiologists or sonographers alone.

The application of laryngeal US is not new within the medical profession and there is considerable mounting evidence to support both the diagnostic ability and feasibility of laryngeal US for diagnosing impairments of vocal fold movement. Laryngeal US has been found to have both high sensitivity and specificity in diagnosing disorders of vocal fold movement in the post-surgical (specifically thyroid) population. Findings of a recent rapid review exploring the utility of laryngeal US for the assessment of vocal fold function revealed a sensitivity and specificity of 100% to detect normal versus disordered vocal fold function with a linear probe with range frequencies (e.g.6-13Hz) (Allen et al., 2020). To date, there are no studies exploring use of laryngeal US in assessing vocal fold movement in neurological conditions, despite the prominence of vocal fold impairments in this patient group.

In addition to increased accuracy, laryngeal US has many other advantages as an assessment and monitoring tool. Arguably, the greatest advantage of laryngeal US over FNE is its bedside accessibility and potential avoidance of intrusive procedures. This is particularly paramount in patients that require multiple invasive procedures, for example, combined FNE and non-invasive ventilation, cough augmentation, suction, nasogastric tube feeding and high flow oxygen therapy. Furthermore, if evaluation by laryngeal US was led by SLT, it would not require patient transport to Ear, Nose \& Throat (ENT) clinics or presence of an ENT consultant at bedside; potentially expediting access to diagnosis of vocal fold function impairments and reducing cost.

A trained SLT could utilise US to identify presence or absence of vocal fold function impairment in patients with neurological disease. Primary examples are cases where vocal fold impairment is a known or anticipated symptom of the underlying neurological condition (such as brainstem stroke, multiple system atrophy and/or neuromuscular conditions such as Charot Marie Tooth disease). In these cases, the SLT could assess using laryngeal US to ascertain a vocal fold diagnosis to inform timely management or treatment plan. In cases where intrusive respiratory interventions may provoke issues with vocal fold movement (such as cough augmentation) the SLT can provide non-invasive 'real-time' monitored laryngeal US assessment which will directly influence combined SLT and physiotherapy management in patients with combined bulbar and respiratory disease. They could also use US to inform the relative urgency of subsequent ENT opinion. This is particularly pertinent at NHNN where there is no on-site access to ENT.

This research project is designed to improve the care pathway for patients with suspected vocal fold mobility impairment secondary to neurological disease. The current standard of practice for patients with suspected impairment of vocal fold mobility at our tertiary neurological centre is referral for routine assessment by an ENT doctor. The timescale from referral to assessment can be up to 12 weeks. FNE is an intrusive procedure requiring placement of a flexible scope into the throat via the nose. This can be uncomfortable for patients and, in some cases, contraindicated (Langmore, 2001). The clinical cost of an ENT-led nasendoscopy is £645. The procedure also requires pre- and post- assessment time and expertise for decontamination of the nasendoscope. Whereas, the cost of the US, led by and SLT is £62. The decontamination process is quick (using a simple wipe) and therefore more cost effective. Laryngeal US examination can be performed by an SLT within 48 hours of referral, leading to more timely assessment and intervention. Furthermore, preliminary findings from our patient advisory group indicate that US is a more comfortable and tolerable assessment. The outcomes of this study has the potential to influence clinical pathways at our tertiary centre to provide a service that is rapid, non-intrusive and cost-effective in the assessment for early diagnosis and management of vocal fold impairment.

This is a prospective cross-sectional mixed-methods study of consecutive patients referred from our tertiary neurological centre to ENT services for an assessment of their vocal fold mobility.

The study is to be conducted at a single-site, specialist tertiary centre, specialising in the diagnosis, assessment, and management of neurological disorders. It will adopt a cross-sectional design and aim to capture consecutive in- and out-patients with suspected vocal fold movement impairment referred to ENT for vocal fold assessment over the course of 12 months.

The anticipated sample size is n=50 patients.

Each research participant will be assessed once. The assessment will include the following (in order):

1. Invitation to participate which will include a patient information leaflet.
2. Signed consent.
3. TWO assessments, one of which is part of routine clinical care. These assessments are FNE and ii) Laryngeal US. FNE will be performed either by an ENT consultant or experienced SLT. A small, flexible camera is passed into the nose to view the throat. This assessment is part of routine clinical care (and is the current gold-standard for assessment for vocal fold movement. Laryngeal US uses a hand-held probe on the skin of the neck to assess the throat from the outside. Lubricating gel is used to improve contact between the skin and the probe. Each assessment will take less then 10 minutes to perform.
4. Participant survey. Each participant will be asked to complete a short (5-item) questionnaire to capture their experiences of undergoing each assessment.

As per usual clinical care - participants will receive a diagnosis from the ENT consultant based on the images from the FNE. They will be offered the opportunity to be contacted about the findings of the research study once data analysis is complete.