In the present study, we evaluated the swallowing function of the sarcopenic elderly without dysphagia. The average score of EAT-10 was significantly greater in sarcopenia group. This might be an evidence of the reduced swallowing function in sarcopenia group although all the participants still preserved the ability to eat orally at the time of referral, since higher scores on the EAT-10 indicate patients’ perception of more severe swallowing problems (18, 22). A previous study showed the EAT-10 score is associated with nutritional status and activities of daily living (ADL) in elderly individuals requiring long-term care (23). Also, serial administration of the EAT-10 has been shown efficacious in documenting initial symptom severity and in monitoring treatment efficacy (18, 24).
The time needed to consume 100 ml of water was significantly longer in sarcopenia group. This might be another evidence of the reduced swallowing function in sarcopenia group. Nathadwarawala et al. first used objective swallowing speed to assess swallowing function and found that swallowing speed was significantly reduced in subjects with swallowing problems (25). Furthermore, a swallowing speed of below 10 ml/s was proposed as the cutoff point for defining swallowing dysfunction (26). This phenomenon probably reflects the compensated or adapted mechanics used by many individuals before an overt clinical problem develops (25, 27). Individuals with swallowing dysfunction may reduce the size of the swallowed bolus to reduce the risk of aspiration, thus slowing their swallowing speed (27).
The sarcopenia group represented greater hyoid bone displacement in swallow of 3 mL water. To our knowledge, our study is the first to investigate the relationship between hyoid bone movement and sarcopenia. There was only one case report about a patient with sarcopenic dysphagia. It showed that the maximum amounts of displacements and maximum moving velocities of the hyoid bone during swallowing were improved after rehabilitation (28). Previous research showed that in an older population with dysphagia, the hyoid bone elevated farther than normal for small bolus sizes, but the patients were unable to maintain this strategy in larger bolus swallows, and the distance of hyoid elevation diminished to normal or below normal levels (29). It is hypothesized that greater displacement reflects compensation for insufficient upper esophageal sphincter opening, and this compensation may break down with larger boluses in patients with dysphagia (29). If so, one implication of our finding would be the clinical application of restricted bolus volume in sarcopenic patients with or without dysphagia. In the meanwhile, strategies and therapies designed to improve the distance of hyoid elevation may be helpful (28).
Our results showed that there was no significant difference between the sarcopenia group and healthy counterpart regarding the tongue pressure. A study conducted in 2015 showed that decreased tongue pressure is associated with sarcopenia elderly (9). However, 42.3% of their subjects had dysphagia, and all their subjects were hospitalized when enrolled. Also, they only included very elderly (age 75 or older) subjects. Another study conducted in Japan showed that sarcopenia is one of the independent explanatory factors for decreased maximum tongue pressure (9). Their study also enrolled hospitalized patients and some of them had dysphagia. Ours only enrolled community dwelling elderly without dysphagia. Histologically, the swallowing muscles are of different embryological origin from somatic muscles, and receive constant input stimulation from the respiratory center (5). Although the swallowing muscles are striated, their characteristics are different from those of skeletal muscles. Features common to sarcopenic appendicular muscle, i.e., a shift to slower myosin heavy chain isoforms, type II muscle fiber atrophy and neuromuscular junction dysmorphology, are absent or minimal in rat tongue muscles (30, 31). In particular, the styloglossus muscle has been shown to exhibit resistance against sarcopenia both molecularly and immunohistochemically (32). It was reported that normal and effortful swallow pressures do not decline with age (13) and by some measures tongue functional reserve is maintained with age (33). Those results suggested tongue muscles may be resistant to sarcopenia at an early stage, and that age-related decline in tongue motor performance may be non-myogenic in origin.
This study had a few limitations. First, we did not evaluate the muscle mass related to swallowing. Second, we were not able to stratify the sarcopenic patients according to their severity. Third, this study was carried out in a single region, and included only community-dwelling elderly without dysphagia within that location. A follow-up study including an expanded target area and sarcopenic patients with dysphagia is required in the future.