Novel and Validated Approaches for Gastric Emptying Scintigraphy in Patients with Suspected Gastroparesis

Controversy exists regarding the relation of upper gastrointestinal symptoms to gastroparesis, which centers on the reportedly weak correlation between symptoms and gastric emptying (GE) measurements. Appropriate management of patients with suspected gastroparesis thus requires the use of validated assessments of GE. GE scintigraphy (GES) using a low-fat EggBeaters (chicken egg white) meal (ConAgra Foods Inc., Omaha, NE, USA) [1] is regarded as the gold standard due to standardized procedures, methods, and well-established normal values. Although this meal has the advantage of good tolerability by the majority of symptomatic patients, there are potential drawbacks: a few patients may not tolerate any solid meal, or the low fat and caloric content may not be able to adequately stress the system, failing to identify impaired gastric motor function in a subset of individuals. Therefore, identification of an alternative, appropriate test meal may be important for clinical and research applications. In this issue, Sachdeva et al. [2] compared GE of the low-fat EggBeaters solid meal (255 kcal containing 2 % fat, 24 % protein, 72 % carbohydrate, and 2 % fiber) to an Ensure Plus (Abbott Laboratories, North Chicago, IL, USA) liquid meal (350 kcal containing 28 % fat, 15 % protein, 57 % carbohydrate, and no fiber) to identify a valid alternative for patients unable to consume the standard low-fat egg-white meal. On separate days, 20 healthy volunteers participated in a well-designed prospective study comparing GES with these two meals; simultaneously, the authors evaluated gastric contractility using a wireless motility capsule (WMC) during both assessments. The objectives were to demonstrate feasibility and to provide hypothesis-generating data (e.g., definition of coefficient of variation [COV; standard deviation/mean] to facilitate the design of future studies). The conclusion that GE of a liquid nutrient meal is similar to that of low-fat egg-white meal (of similar calorie content) is valid, at least in healthy subjects. Nevertheless, as acknowledged by the authors, their results will require replication in a larger cohort, and in subjects with suspected gastroparesis who might differ from a healthy population in terms of having differential GE of solid versus liquid meals. Jones et al. [3] previously reported a significant but weak (r = 0.42, p \ 0.01) correlation between GE of solids and nutrient-containing liquids among 86 patients with diabetes mellitus. In the study by Sachdeva et al. [2], the correlation between the GE T1/2 of the two meals was similarly weak (r = 0.53) among healthy subjects, suggesting that there are significant intraindividual differences in the emptying of the two meals, and that less than 30 % of the variance is attributable to the same mechanisms for emptying of the two types of meals. It is also necessary to clarify the inter-individual COV with the EggBeaters and the liquid nutrient meal. Diagnostic interpretation of GE T1/2 by GES in an individual patient requires robust definition of the intra-individual COV with the specific meal used. Thus, the estimated COVinter for GE T1/2 was 25 % with the EggBeaters meal and 24 % using a meal of higher fat and calorie content [4] in which the solid phase is radiolabeled. With the latter radiolabeled solid meal, the COVinter for GE at 4 h was 9.6 %, confirming the recommendation by Tougas et al. [1] that the percent retention at 4 h is an endpoint useful for gastroparesis screening. Similarly, others have shown greater sensitivity of detection of abnormal GE with use of M. Camilleri (&) A. Shin Mayo Clinic, Charlton 8-110, 200 First St. S.W., Rochester, MN 55905, USA e-mail: camilleri.michael@mayo.edu