As the esophagus is a commonly involved organ of SSc, a practical and convenient screening tool to objectively evaluate the existence and severity of esophagus status is still lacking. The novelty of our study is that we first reported a spectrum of US parameters that can be used to detect the esophagus involvement in SSc patients, and that these new parameters correlated to SSc clinical and CT markers.
The US parameters we used in this study are summarized from literature which mostly reported the US evaluation of GERD in infants and children(13). In the literature, abdominal esophagus length is a commonly adopted parameter, and is shorter in GERD patients as compared to normal controls in our and previous studies(2, 21, 24). The underlying reason is complicated, possibly due to the fibrosis and contracture of the esophagus wall in SSc. It has been reported that the reflux detected by US has high sensitivity and positive predictive value with reference to pH monitoring in children(14, 25). In our study, we found reflux a discriminating parameter between SSc and control group, yet the sensitivity is to be determined.
His angle was reported to be a stable, age-independent parameter, which is larger in GERD patients than controls(26, 27). We found that His angle was larger in SSc patients than controls, which confirmed the previous findings(28). Moreover, the angle change before and after water intake was larger in patients than in controls, which is not reported previously. This can be explained by that the stiffness of the esophagus and stomach wall in SSc decreases the elasticity, making it harder to maintain the original form under pressure, and reflected as a bigger angle change.
The esophageal wall thickness and esophageal SWE failed to show good repeatability in our study. Although SWE can theoretically give quantitative measurements to reflect esophageal fibrosis, it is highly affected by the heartbeat, breath, and complicated tissue texture during our practice. Further research is needed to find a suitable way to use SWE.
In our study, US parameters had a fair-to-good correlation with CT parameters (Dmax, %Eop). No previous studies had reported the correlation between the two imaging modalities. Our study proved that although evaluating esophagus from different perspectives, US and CT can be complementary tools to reflect esophagus condition in SSc. GERDQ is considered as an auxiliary method in GERD diagnosis, which has a positive correlation with His angle in our study. These results imply that US is able to evaluate the esophagus status in SSc patients.
Accumulating evidence has suggested that esophageal disease may be an independent contributor to ILD, a condition that is strongly associated with increased morbidity and mortality(6, 9, 29). Previous studies have shown a negative correlation between esophagus dilation and pulmonary function test(6, 9, 29). Our study demonstrated that SSc patients with reflux on US tend to have higher ILD scores than patients with no reflux, confirming the relationship between esophagus dysfunction and ILD in SSc. We did not find correlations between US parameters and pulmonary function test indicators, possibly due to the small sample size.
Our results failed to find the association between US parameters and mRSS. Since the enrolled SSc patients were not naïve, the skin thickness is under the influence of the long-term medication, which disturbs the original condition of the skin.
There are several limitations to our study. First, we did not compare US parameters with classical examination methods for GERD, such as 24-hour pH monitoring, barium esophagography, esophageal manometry, or upper GI endoscopy, due to their complexity and invasiveness leading to the limited use in China. Another obvious limitation is that the sample size is relatively small despite our promising findings, which leaves the validation of our preliminary results for future studies.