How is gastroparesis diagnosed?
The most common method for diagnosing gastroparesis is a nuclear medicine test called a gastric emptying study, which measures the emptying of food from the stomach. For this study, a patient eats a meal in which the solid food, liquid food, or both contain a small amount of radioactive material. A scanner (acting like a Geiger counter) is placed over the stomach for several hours to monitor the amount of radioactivity in the stomach. In patients with gastroparesis, the food takes longer than normal (usually more than several hours) to empty into the intestine.
The antro-duodenal motility study is a study that can be considered experimental and is reserved for selected patients. An antro-duodenal motility study measures the pressure that is generated by the contractions of the muscles of the stomach and intestine. This study is conducted by passing a thin tube through the nose, down the esophagus, through the stomach, and into the small intestine. With this tube, the strength of the contractions of the muscles of the stomach and small intestine can be measured at rest and following a meal. In most patients with gastroparesis, food (which normally causes the stomach to contract vigorously) causes either infrequent contractions (if the nerves are diseased) or only very weak contractions (if the muscle is diseased).
An electrogastrogram, another experimental study that sometimes is done in patients with suspected gastroparesis, is similar to an electrocardiogram (EKG) of the heart. The electrogastrogram is a recording of the electrical signals that travel through the stomach muscles and control the muscles’ contractions. An electrogastrogram is performed by taping several electrodes onto a patient’s abdomen over the stomach area in the same manner as electrodes are placed on the chest for an EKG. The electrical signals coming from the stomach that reach the electrodes on the abdomen are recorded at rest and after a meal. In normal individuals, there is a regular electrical rhythm just as in the heart, and the power (voltage) of the electrical current increases after the meal. In most patients with gastroparesis, the rhythm is not normal or there is no increase in electrical power after the meal. Although the gastric emptying study is the primary test for diagnosing gastroparesis, there are patients with gastroparesis who have a normal gastric emptying study but an abnormal electrogastrogram. Therefore, the electrogastrogram can be useful primarily when the suspicion for gastroparesis is high but the gastric emptying study is normal or borderline abnormal.
A physical obstruction to the emptying of the stomach, for example, a tumor that compresses the outlet from the stomach or scarring from an ulcer, may cause symptoms that are similar to gastroparesis. Therefore, an upper gastrointestinal (GI) endoscopy test usually is performed to exclude the possibility of obstruction as the cause of a patient’s symptoms. (Upper GI endoscopy involves the swallowing of a tube with a camera on the end and can be used to visually examine the stomach and duodenum and take biopsies.)
Upper GI endoscopy also may be useful for diagnosing one of the complications of gastroparesis, a bezoar (a clump or wad of swallowed food or hair). Because of the poor emptying of the stomach, hard-to-digest components of the diet, usually vegetables, are retained and accumulate in the stomach. A ball of undigested, plant-derived material can accumulate in the stomach and give rise to symptoms of fullness or can further obstruct the emptying of food from the stomach. Removing the bezoar may improve symptoms and emptying.
A computerized tomographic (CT) scan of the abdomen and upper gastrointestinal X-ray series also may be necessary to exclude cancer of the pancreas or other conditions that can obstruct the emptying of the stomach.
An alternative method of looking at gastric emptying is a large capsule (SmartPill) that is swallowed. The capsule measures pressure, acidity, and temperature, and then transmits the measurements wirelessly to a recorder. By analyzing the measurements it can be determined how long it takes the capsule to empty from the stomach, and the amount of time necessary for emptying correlates well with other measures of gastric emptying.