William L. Hasler, MD

Disclosures

Medscape J Med. 2008;10(1):16 

In This Article

Documentation of Impaired Gastric Function

Gastric scintigraphy is the most accepted test for diagnosing gastroparesis; it employs 99mTc-sulfur colloid bound to solid food. A major drawback of gastric scintigraphy has been a lack of standardization of criteria used to diagnose gastroparesis across all medical centers. In a Canadian hospital survey, 28% of centers defined the cutoff for gastroparesis as the degree of gastric retention greater than 2 standard deviations above the mean, whereas 26% used 1 standard deviation, 6.5% employed 1.5 standard deviations, and 40% had no objective criteria.[95] Only 18% of centers validated their results in healthy volunteers. Recently, researchers have advocated uniform standards for gastric scintigraphy performance and interpretation. A standardized method using a meal of toast, jam, and an egg substitute with 99mTc-sulfur colloid has been validated.[96] Gastric retention greater than 60% at 2 hours and greater than 10% at 4 hours is diagnostic of gastroparesis. Even using standardized protocols, the diagnosis of gastroparesis may not be clear-cut. In one investigation, 37% of patients with normal emptying at 2 hours exhibited delayed emptying at 4 hours, whereas 19% with delayed emptying at 2 hours normalized at 4 hours.[97] The use of gastric scintigraphy has not been rigorously subjected to outcomes analysis. One study reported that emptying results do not influence clinical management.[98]

Other techniques for measuring gastric emptying have also been promoted. Results of breath testing after consuming nonradioactive 13C-labeled nutrients such as octanoate and acetate can assess gastric emptying of solids and liquids. These methods measure liberation of 13CO2 in expired breath samples after duodenal assimilation of the ingested compound and are reliable only in persons with normal digestive and absorptive function. Emptying results from 13C-octanoate and 13C-acetate breath tests show fair-to-good correlations with scintigraphy.[99] A second method involves swallowing a radiotelemetry capsule that continuously transmits information on luminal pH and pressure to a receiver worn by the patient. With this test, gastric emptying is detected by the abrupt pH increase as the capsule passes from the antrum to the duodenum. Correlation coefficients between capsule and scintigraphic emptying times exceed 0.8.[100] This method also quantifies gastric motility indices as well as transit, pH, and motor patterns in the small intestine and colon. Measures of gastric emptying can also be provided by ultrasonography and magnetic resonance imaging.[101,102] A variant of gastric scintigraphy, dynamic antral scintigraphy, has been used in research to image nonocclusive antral contractions in real time, but this method has not been used clinically.[103]

Antroduodenal manometry involves peroral placement of a catheter to monitor luminal pressure patterns. Fasting motility is recorded for 4-5 hours, during which time 1 or more fasting motor complexes are usually observed. Fed motor activity is then measured for 2 hours after a solid meal. In some centers, 24-hour ambulatory recordings or testing of motor effects of prokinetic drugs are performed. Manometry is indicated for patients who have unexplained symptoms and have not responded to treatment, or who are being considered for surgery or enteral vs parenteral nutrition.[104] Gastroparesis is characterized by loss of normal fasting migrating motor complexes and reduced fed antral contractions and, in some cases, pylorospasm.[16] Manometry is most useful in excluding associated small intestinal dysmotilities, including those with myopathic (contractile amplitude < 30 mmHg with normal morphology) and neuropathic (intense, uncoordinated burst contractions) patterns. Small intestinal motor dysfunction is detected in 17% to 85% of patients with gastroparesis.[17] Clinical management is influenced in approximately 20% to 25% of patients undergoing gastrointestinal manometry.[105]

Electrogastrography (EGG) measures gastric slow-wave activity via cutaneous electrodes overlying the stomach. In healthy persons, EGG recordings exhibit uniform waveforms of 3 cycles per minute, which increase in amplitude after ingesting water or nutrients. EGG abnormalities include rhythm disruption for more than 30% of the recording time including tachygastria (frequency of more than 4 cycles per minute) and bradygastria (fewer than 2 cycles per minute) and lack of a signal amplitude increase with eating.[106] EGG abnormalities are prevalent in patients with gastroparesis as well as in some patients with nausea and vomiting and normal emptying. Impaired postprandial amplitude responses correlate with delayed solid emptying in gastroparesis.[107] The importance of EGG dysrhythmias in symptom generation is supported by observations that treatment responses correlate better with slow-wave normalization than with accelerated emptying.[108] Other electrical techniques, such as epigastric impedance and applied potential tomography, employ cutaneous electrodes to measure changes in resistance afforded by liquid meals which correlate with the rate of emptying. Tests of myoelectric function have been promoted as alternatives to gastric scintigraphy, but have not achieved widespread acceptance due to a lack of proven gastric antiarrhythmic therapies.[106]

Other tests of gastric motor function are useful research tools but have limited clinical applicability. Single photon emission computed tomography (SPECT) employs intravenous 99mTc-pertechnetate that accumulates within the gastric wall, providing a 3-dimensional outline that can assess fundic accommodation.[109] Satiety testing involves the ingestion of water or a liquid nutrient until the patient reports maximal fullness. Volumes consumed in functional dyspeptics with early satiety are reduced vs healthy volunteers, reflective either of impaired accommodation or visceral hypersensitivity.[110]

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