A Feasibility Study to Investigate the Accuracy and Viability of Ultrasound in Detecting Impairments of Vocal Fold Mobility in People With 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.