Craniofacial Muscles

11 Laryngeal Muscle Response to Neuromuscular Diseases and Speci fi c Pathologies
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In the ALS limb group, vocal fold mobility demonstrated a slight deviation from
normal in nine out of 11 patients. Sluggish movement of both vocal folds and lack
of complete closure during phonation were detected in three participants. There was
a unilateral decrease in tension and mobility of the vocal fold in four cases and vocal
fold bowing in two others. However, audio-perceptual assessment of the voice
qualities of the limb onset patients revealed no disturbances to vocal pitch.
Bulbar onset participants with predominantly lower motor neuron involvement
presented with smooth vocal fold edges and decreased vocal fold mobility and
adduction during the respiratory phase. During phonation, some patients showed
lack of complete vocal fold closure, with an hourglass shaped glottis closure pattern.
In these cases, voice quality was described as husky and low. For bulbar onset
participants classi fi ed as predominantly upper motor neuron, their presentation
demonstrated slight disturbances with mobility, hypoadduction of the vocal folds,
and hyperadduction of the ventricular folds. The vocal folds were described as
thicker, and voice production was characterized by increased tension in the cervical
musculature causing a harsh, strain-strangled voice quality, similar to that heard in
spasmodic dysphonia (Tomik et al. 2007 ; Lundy et al. 2004 ) . In addition, this group
demonstrated a hypernasal quality.
These distinct laryngeal and voice quality fi ndings may be used to supplement
other clinical diagnostic tools especially with individuals suspected of presenting
with bulbar onset ALS. Indeed, it has been suggested that early bulbar signs such as
reduced voice frequency range and phonatory instability may be present in patients
with ALS before the occurrence of perceptually aberrant vocal characteristics
(Silbergleit et al. 1997 ; Watts and Vanryckeghem 2001 ) . Another frequent laryngeal
symptom of ALS that occurs when the respiratory muscles become weak is dyspnea.
Dyspnea may also result from a narrowing of the glottis due to paresis of the PCA
muscles, the vocal fold abductors. This paresis may lead to laryngeal symptoms
including hoarseness, hypophonia, and short phonation time to nocturnal nonproductive
cough and attacks of inspiratory stridor and shortness of breath (van der
Graaff et al. 2009 ) .
Beyond the laryngeal function of voice quality is the vegetative function of swallowing.
The laryngeal musculature is responsible for the protection of the airway
during this life-sustaining event. Laryngeal muscle paresis leading to reduced glottal
closure may lead to swallowing problems. Indeed, mortality in the ALS population is
often associated with aspiration pneumonia. Although typically considered only as a
motor neuron disease, Amin et al. ( 2006 ) studied the contribution of sensory dysfunction
as a contributor to this disease process. The sensation of the larynx was
studied in 22 patients with ALS with abnormal sensation found in 54.5% of the tested
population. The authors concluded that in addition to muscle weakness, decreased
sensation may also contribute to the swallowing dif fi culties of individuals with ALS.
Very little is known of the exact laryngeal muscle biological response to ALS,
although a handful of quantitative studies examining motor end plates and other
histological and physiological studies have been conducted in selected ILM (Gambino
et al. 1985 ; Kanda et al. 1983 ; Yoshihara et al. 1984, 1991 ; Nomoto et al. 1991 ) .
Yoshihara et al. ( 1998 ) examined the TA and PCA muscles in four patients with ALS