Discussion
dysphagia, comorbidity, pneumonia, fatigue, acute stroke, neurodegenerative diseases, pulmonary disease, weight loss, muscle fatigue
DYSPHAGIA, PNEUMONIA, ACUTE STROKE, NEURODEGENERATIVE DISEASES, ASPIRATION PNEUMONIA, PULMONARY DISEASE, DISEASES
No significant differences were observed in the PAS and FDS total scores according to the contrast agent used in the test. This might suggest that the difference in physical properties of the two contrast agents is not critical enough to make a difference in the anatomical depth to which food bolus penetrates when ingested. However, significant differences between the two contrast agents were seen in the FDS subcategories, scores for “residue in pyriform sinuses”. The reason for this difference between PAS and FDS scores could be because the FDS was developed to supplement PAS and it can report more qualitative aspects of VFSS findings than PAS. Additionally, a greater number of swallows were required with barium sulfate than with iohexol. According to a previous study, iohexol demonstrated a faster transit time in gastrointestinal studies than barium sulfate because iohexol has higher water solubilityOur study reveals that a longer oral transit time and greater number of swallows when testing with barium sulfate were associated with the development of subsequent pneumonia after VFSS. Of note, when these two factors were analyzed using ROC analysis, only the number of swallows demonstrated an excellent diagnostic value for predicting subsequent pneumonia. According to previous studies, prolonged swallowing time, including oral transit time, is associated with an increased risk of aspiration pneumoniaOur study also found significant differences in VFSS findings including oral transit time, coating of the pharyngeal wall after swallowing, and number of swallows in participants with and without unintentional weight loss when using barium sulfate. By contrast, when using iohexol, oral transit time, nasal penetration, residue in the valleculae, PAS scores, and number of swallows demonstrated significant differences between those with and without unintentional weight loss. Among these findings, oral transit time and the number of swallows when using barium sulfate had acceptable diagnostic values for predicting unintentional weight loss; however, the number of swallows when using iohexol may have an excellent diagnostic value for predicting unintentional weight loss, while the PAS scores when using iohexol had an acceptable diagnostic value. Similarly to subsequent pneumonia discussed earlier, due to the VFSS protocol of our study, oral transit time and number of swallows are thought to be able to better indicate the efficiency of swallowing compared to other metrics. Additionally, it is well known that unintentional weight loss is significantly associated with dysphagiaTo the best of our knowledge, this is the first study designed as a randomized, controlled, crossover trial to directly compare barium sulfate and iohexol as contrast agents for VFSS in predicting subsequent pneumonia and unintentional weight loss in patients with dysphagia. Because the two contrast agents were compared in the same participants, minimizing the influence of different patient characteristics on the results of the analysis was possible. Previous studies that compared barium sulfate and iohexol as contrast agents for VFSS focused on safety when the participants aspirated during the test, and since each contrast agent was administered to two different groups, the possibility of selection bias could not be completely excluded even if factors including age and sex were controlled.However, this study has several limitations. First, the sample size was relatively small; future studies with larger sample sizes would provide more information for selecting the superior contrast agent between barium sulfate and iohexol. Second, underlying diseases of the participants were varied without restrictions. For example, although the characteristics and/or clinical course of dysphagia in patients with acute stroke and those with neurodegenerative diseases can be very different, our study was conducted without excluding specific diseases or targeting only specific diseases. To compare the ability of contrast agent to predict long-term prognosis of dysphagia, including various underlying diseases may have advantages in terms of generalizability, but the limitations due to this are also clear. Also, it should be noted that that although the statistical significance was not reached, more participants in barium sulfate-first group had pulmonary disease as medical comorbidity, which has close association with pneumonia and unintentional weight loss. Third, inability for blinding to the contrast agents used in the VFSS was another limitation of this study. Forth, the IDDSI levels of the two contrast agents were different, and this might well affect the study outcomes. Future study using equal IDDSI level of the liquid barium sulfate and iohexol would be necessary to better understand how the different physical properties of the two contrasts other than viscosity affect findings of VFSS. Fifth, subsequent pneumonia does not necessarily mean aspiration pneumonia. Despite efforts to include only aspiration pneumonia in the analysis, the possibility that other types of pneumonia may also be included cannot be completely ruled out. Sixth, although efforts were made to reduce the difference and make the conditions for testing the two contrast agents as similar as possible, muscle fatigue, which can be induced by performing multiple swallowing motions during the VFSS, may have had an effect for the results. To reduce the effect of fatigue, further study testing the two contrast agents in a differentiated participants would be needed. Last, we assumed that the previously administered contrast agent did not affect the subsequent VFSS findings; however, the lack of a washout period might have affected the study results. Although the previously used contrast agent was not detected using fluoroscopy, it might have affected the subsequent VFSS findings.