Reduced Tightening of Pharynx Underlies Impaired Swallowing in ALS Patients, Study Reports

Impaired tightening of the pharynx is associated with inefficient swallowing in patients with amyotrophic lateral sclerosis (ALS), according to a new study.

The study, “Reduced pharyngeal constriction is associated with impaired swallowing efficiency in Amyotrophic Lateral Sclerosis (ALS),” appeared in the journal Neurogastroenterology & Motility.

Dysphagia, a swallowing problem, is an ALS symptom that leads to prolonged mealtimes, mealtime fatigue, and reduced quality of life. However, the physiological mechanisms leading to impaired swallowing remain unclear.

Although formation of residue in the pharynx, part of both the digestive and respiratory systems, is a known risk factor for aspiration of food into the airways and is linked to the development of malnutrition, most dysphagia studies in ALS patients have focused on swallowing safety, not efficiency.

Possible mechanisms contributing to swallowing inefficiency include decreased pharyngeal pressures and motility, and reduced tongue contact to the pharyngeal wall. Lower pharyngeal strength and constriction, or tightening, have been proposed as contributors to the presence of pharyngeal residue in the elderly and in people with dysphagia following stroke.

The research team intended to characterize various parameters of swallowing efficiency and pharyngeal tightening in patients with ALS and assess whether volume and thickness of the bolus (a mixture of food and saliva formed during chewing) affect pharyngeal tightening and/or swallowing efficiency.

The investigators also worked to determine whether reduced pharyngeal tightening, meaning a larger area during swallowing, correlates with impaired swallowing efficiency in ALS.

They hypothesized that ALS patients would show less pharyngeal tightening during swallowing compared to healthy individuals, which would correlate with disease severity and the presence of bulbar symptoms, which, besides dysphagia, may also include dysarthria (slowed or slurred speech).

The team also hypothesized that larger or thicker boluses induce less tightening due to increased bolus weight and/or inability of the swallowing mechanism to adapt, while also being associated with increased post-swallow residue and number of required swallows to clear the bolus.

A total of 26 adults (14 men) with ALS underwent videofluoroscopic examinations — a form of real-time X-ray. Eight had bulbar-onset ALS, 17 had spinal-onset ALS, and one had a mixed-onset profile. Their mean age was 63 (range 30-75) and average symptom duration was 24 months (1‐54).

Each patient swallowed 3 and 20 mL of thin liquid, as well as 3 mL of pudding-thick liquid. The scientists recorded the total number of swallows per bolus and obtained measures of pharyngeal tightening and post-swallow residue in the vallecular and pyriform sinuses, known as the pharyngeal side pockets where food may deposit.

Results showed reduced tightening and increased residue in ALS patients, compared to data of healthy controls. Bulbar-onset patients showed more pronounced impairment of pharyngeal tightening than those with spinal onset.

A total of 15 participants (58%) presented with vallecular residue, while 35% exhibited pyriform residue on at least one bolus trial.

Reduced tightening significantly affected the presence of post-swallow residue as well as the number of swallows per bolus. The data also showed that thicker bolus was associated with increased residue in the vallecular sinus, while increased bolus volume correlated with decreased pharyngeal narrowing.

The results further demonstrated that lower (worse) bulbar subscores on the ALS functional rating scale (ALSFRS-R) were associated with less tightening. No relation was found with symptom duration or with ALSFRS‐R total score.

The larger 20 mL thin liquid task induced less tightening, while the pudding‐thick bolus caused greater vallecular residue.

“As thicker liquids flow more slowly and are shown to reduce aspiration in many populations, the prescription of thickened liquids to individuals with ALS who aspirate may still be clinically justified,” the researchers wrote.

“Our results suggest that reduced pharyngeal constriction is a significant physiological parameter related to swallow inefficiency in ALS,” they added.

Among the study’s limitations, the team mentioned the small sample size and the limited range of disease severity. Future studies should have more participants and focus on the oral phase of swallowing, the authors wrote. Research evaluating how swallowing changes throughout the course of  ALS are also warranted, they added.