An uncompromised efferent vagal innervation within the larynx is visually assessed by asking the patient to perform a series of tasks. In the following, we will describe these tests according to assessment of spontaneous and/or pathologic movements of the entire larynx in an overview endoscopic position with either (1) uni- and/or bilateral recurrent laryngeal nerve (RLN) function or (2) superior laryngeal nerve (SLN) function.

Positioning the tip of a flexible, transnasally routed endoscope at the height of the uvula enables an overview of the larynx, hypopharynx, and base of tongue. It also allows for assessment of bolus/saliva retentions in the piriform sinuses and valleculae. Assessment of quiet breathing, phonation, vegetative maneuvers such as throat clearing and coughing, quick diadochokinetic adduction-abduction tasks such as laughing, and swallowing of fluid/solid bolus gives an overview of biomechanical function of all structures in this region. Focus is always on anatomical structures, left-right symmetry, range of motion of arytenoids and of vocal folds, ability of tensioning vocal folds, and speed of motion within tasks, including special attention targeted at unilateral “lagging” of movements (reduced speed or latency differences). A key point is immobility or hypomobility in contrast to normally expected mobility of any of the aforementioned structures. For diagnostic assessment of neurolaryngological disorders, it is of crucial importance to also look for tremor, myoclonus, paradoxical movements, etc. [5].

The most common neurolaryngological disorder is motor RLN paresis or paralysis which leads to hypomobility or immobility of the affected side. RLN-related disorders are frequently unilateral, but of course they can be bilateral. While it is in most cases rather easy to visualize a unilateral paralysis with immobility of one side, a slight unilateral hypomobility may be difficult to detect and requires a comprehensive examination. A slight bilateral hypomobility can also be hard to verify because the comparison with the contralateral side is unreliable.

Checking for adduction-abduction diadochokinesis while asking for rapid changes of forced nasal sniffing and hard onset phonation of /eee/ (e.g., using an /eee/−sniff test) can reveal impaired range of motion and lagging of the arytenoids. Phonation of /eee/ in chest and falsetto voice, each for at least 5 s, while keeping the sound as stable as possible, should enable assessment for tremor as well as provide enough time for stroboscopy. Inspiratory phonation facilitates visualization of true vocal folds in cases of overlying ventricular folds in chest voice phonation, because inspiratory phonation induces adduction of vocal folds and abduction of ventricular folds.

When checking vocal folds for underlying neurolaryngological disorders, keep in mind that motor branches of the RLN affect muscular actions that primarily move the arytenoid cartilage. Thus, comprehensive assessment of actively inducible arytenoid movements for rocking, gliding, and tilting is the primary target for neurolaryngological diagnostics. The cartilage’s most easily visible part is the vocal process, and thus this prominent structure should be inspected first (and not only the arytenoid hump or the membranous part of the vocal fold). Examiners should look for active abductory and adductory movements of the vocal process, its range of motion and symmetry of motion when compared with the contralateral side, movement lagging, and level differences. In cases of side asymmetry, it goes without saying that the hypomobile side is the affected side.

In bilateral hypomobility, a posterior glottic stenosis is an important differential diagnosis one has to keep in mind. In most cases it can be seen with special laryngoscopic techniques such as flexible endoscopy with intralaryngeal tip position (use the “dipping maneuver” to inspect the posterior inferior part of the endolarynx at the level of the vocal processes). In some cases an examination in general anesthesia can be necessary for exclusion of posterior glottic stenosis.

Within differential diagnosis of vagal lesions, the assessment of superior laryngeal nerve (SLN) impairment is mandatory. The quickest way to examine the motor function of the SLN is to ask for a glissando (gliding sound like a siren within a few seconds) of an /eee/ vowel from low-pitch phonation in chest voice up to the highest notes in falsetto voice and then gliding back down. Impairment of SLN function should be audible as inability of performing this task, inability to phonate in falsetto register, inability to perform a glissando without sound breaks, or when more roughness is audible while increasing pitch. Visually, the vocal folds show failure in getting elongated (unilaterally or bilaterally – due to impairment of the cricothyroid muscle to contract).

When assessing uni- or bilateral impairment of the motor function of the SLN or RLN, the use of laryngeal electromyography (LEMG) is very helpful. Because details are provided in a special chapter in this book, we just mention the different ways of needle placement in this chapter. Needles can be positioned indirect transorally or percutaneously, (e.g., with monopolar and bipolar needles or hooked wire electrodes). With special techniques, all laryngeal muscles can be assessed with LEMG [7]. Although the CT muscle is the most superficial muscle, it is a very thin muscle, and therefore needle positioning can be quite challenging. But by far the most difficult muscle to reach is the posterior cricoarytenoid (PCA) muscle.

Although we mostly associate neurolaryngological disorders with motor deficits, we must not forget that afferent deficits may be present in a substantial number of patients and can be the cause of significant problems, not only food aspiration.

Many publications have addressed the assessment of sensitivity testing within in-office procedures. In this chapter we can only briefly touch upon the most important assessment techniques. The etiology of impairment of supraglottal sensitivity is caused by an affection of the supralaryngeal nerve, where nerve problems can be located in the neck, or being part of an upper vagal problem, including all kinds of possible central or peripheral nervous system etiologies. In contrast to calibrated air puff stimulation supplied by a machine through an instrument channel during flexible endoscopy, we propose that soft touching of mucosal surfaces with the tip of the endoscope can also provide a good estimate of surface sensitivity and will suffice in many cases to enable a reliable diagnosis. The most important regions to test are arytenoid humps, epiglottis, and aryepiglottic folds – the so-called aditus ad laryngis. Indirect signs of reduction or loss of mucosal sensitivity can be seen in silent aspiration during swallowing assessment with bolus leakage and retentions and of course as reduced response to touching during flexible endoscopy.