In this study, we assessed the swallowing function in elderly sarcopenic patients without dysphagia. The EAT-10 score was significantly greater in the sarcopenia group than that in the nonsarcopenia group; however, despite the statistical difference, none of the participants’ scores reached the cut point of 3, suggesting dysphagia. Therefore, the differences in EAT-10 scores between the two groups should be interpreted with caution.
The time needed to consume 100 ml of water was significantly longer in the sarcopenia group than that in the nonsarcopenia group, suggesting the swallowing function is reduced in patients with sarcopenia. Buchholz et al. postulated that in dysphagic patients, the swallowed bolus size might be reduced as a compensation strategy, resulting in a slower swallowing speed (23). Nathadwarawala et al. discovered that, in subjects with swallowing problems, objective swallowing speed was significantly diminished (24). Swallowing speed less than 10 ml/s is considered to be a strong predictor of dysphagia (25). Although our sarcopenic participants have not developed dysphagia, the delay in completing the swallowing test reflects the compensatory mechanism (decreased volume per swallow) they developed before clinical problems become apparent (23, 24). To the best of our knowledge, this is the first study to 100 ml WST on elderly individuals with sarcopenia. Yoshitoshi et al. evaluated the swallowing function in bedridden older adults using various bolus sizes (2, 3, and 5 ml of liquid), where the swallowing performance was significantly correlated with the mid-upper arm circumference, rather than the general frailty (26). The overall reduction of lean body mass might involve not only the mid-upper arm circumference but also the swallowing muscles.
The sarcopenia group had greater HD when swallowing 3 mL of water than the nonsarcopenia group. According to our knowledge, this is the first study investigating the relationship between hyoid bone movement and sarcopenia. There was only one case report about a patient with sarcopenic dysphagia, reporting that both the maximal amounts of HD and HV during swallowing were increased after rehabilitation (27). Previous research revealed that in an older population with dysphagia, HD was greater than the normal level in small bolus ingestion; however, the magnitude of HD decreased to normal or was below normal levels in large bolus ingestion (28). It was hypothesized that greater displacement indicated compensation for insufficient UES opening, which could no longer be maintained with larger boluses in dysphagic patients (28). Therefore, our findings included the clinical application of restricted bolus volume in sarcopenic patients with or without dysphagia. Meanwhile, rehabilitative programs for strengthening the hyoid elevation muscles might be useful (27).
Moreover, the sarcopenia group had greater HV when swallowing 3 mL of water than that in the nonsarcopenia group, which involves HD and duration. Previous studies hypothesized that HV is more sensitive in detecting changes in swallowing kinematics than HD alone (29) since studies of age-related changes in HD obtained heterogeneous results (30-32). Furthermore, the decreased HV may slow down the closure of the laryngeal vestibule and opening of UES, thus increasing the risk of aspiration (33). Many studies have already incorporated HV to describe hyoid excursion kinematics during swallowing (29, 33). For instance, Ueda et al. (34) reported decreased hyoid excursion velocity in dysphagic patients; alternatively, previous studies showed that older healthy subjects had greater HV during swallowing than their younger counterparts (29, 35), supporting the concept of adaptation and compensation in the healthy older individuals. Greater HV in our sarcopenic participants may indicate a compensatory response to subclinical changes in the swallowing mechanism. These interpretations are speculative and require future experimental evaluation; however, the results of this study suggest that HV may be a sensitive indicator when assessing the effects of sarcopenia on swallowing performance.
Our results revealed that there was no significant difference between the sarcopenia group and their healthy counterparts regarding tongue pressure. Studies have reported that tongue strengthening could enhance the maximum peak lingual pressures in both healthy adults and dysphagic patients; however, whether the gain in lingual pressures generalizes to the functional improvement in swallowing is still undetermined (36, 37). A previous study done in Japan demonstrated that reduced tongue pressure is correlated with older individuals with sarcopenia (9); however, 42.3% of their subjects suffered from dysphagia, and all their subjects were hospitalized at the time of enrollment. Besides, they only included older subjects who were at least 75 years old. This study only enrolled community-dwelling elderly individuals without dysphagia. Another explanation was based on histological evidence as follows. The swallowing muscles and somatic muscles stem from different embryological origins and the swallowing muscles were continuously activated by the brainstem respiratory center (5). Many common sarcopenic muscle characteristics are rare in the lingual muscles of rats, such as type II muscle fiber atrophy, and change to slower myosin heavy chain isoforms and neuromuscular junction dysmorphology (38, 39). In particular, the styloglossus muscle was unaffected by sarcopenia anatomically and molecularly (40). Besides, it was reported that the elderly can still produce similar noneffortful and effortful swallow pressures compared to younger adults (14) and tongue functional reserve does not decline significantly with age (41). These findings suggest that tongue muscles are not as susceptible to sarcopenia as appendicular muscles and lingual function does not necessarily deteriorate with age.
This study had several limitations. First, we recruited our participants in annual health exams occurring in a local community hospital. Younger elderly individuals were more likely to receive recruiting information and join our study, whereas older people were less likely to be involved. Second, regarding WST, we did not measure the number of sips. Third, we did not assess the muscle mass related to swallowing. Fourth, we could not stratify the patients with sarcopenia according to the severity of the disease. Fifth, this study was conducted in a single region and included only community-dwelling elderly individuals without dysphagia within that location. A follow‐up study including an expanded target area and sarcopenic patients with dysphagia is warranted.