Gastroesophageal reflux disease (GERD) is a common disorder of the gastrointestinal tract that involves the movement of stomach contents into the esophagus or mouth, causing discomfort or complications. Population-based studies have identified GERD as one of the most common upper gastrointestinal (GI) tract disorders, with a prevalence of about 20% in the United States. Patients may present with typical symptoms, including heartburn or regurgitation, or atypical symptoms such as cough, asthma, hoarseness, chronic laryngitis, throat-clearing, chest pain, dyspepsia, and nausea.
Typically, GERD is diagnosed clinically and with the response to a trial of proton-pump inhibitor (PPI) therapy. Relief of heartburn and regurgitation after a 6 to 8 week trial of PPI therapy is a reliable indicator of GERD. This approach has a sensitivity of 78% and a specificity of 54%; hence a negative trial does not rule-out GERD. However, this is a cost-effective approach to diagnosing GERD rather than proceeding directly to endoscopic or alternative diagnostic testing. If patients present with alarm features (i.e., new-onset dyspepsia at age greater than 60, GI bleeding, dysphagia, odynophagia, weight loss, anemia, persistent vomiting), a trial of PPI therapy is not necessary and the work-up should directly proceed to early endoscopy.
Ambulatory esophageal pH testing is done with a wireless pH capsule or a traditional pH probe and is the gold standard test for the diagnosis of GERD. There are some patients with typical or atypical GERD symptoms that have a normal upper endoscopy and normal ambulatory esophageal pH testing but are unresponsive to standard PPI therapy. Ambulatory pH testing does not detect all types of reflux, especially when the refluxate contains little or no acid. It relies on the acidification of intraesophageal pH to less than 4 as a marker for the presence of gastric contents in the esophagus to diagnose gastroesophageal reflux (GER) episodes. Hence, it has limited use in detecting episodes where the pH fails to fall below 4.
A newer technique combining multichannel intraluminal impedance (MII) testing with pH testing, allows for the detailed characterization of the refluxate, including its physical and chemical properties. The MII detects the intraluminal bolus movement with the esophagus via strategic placement of a catheter, and it can characterize, in combination with pH testing, whether the bolus is composed of liquid, gas, or mixed components as well as its pH.
There is no specific specimen that is collected. The study lasts for 24 hours, and once it is complete, the recording unit is returned to the provider. The information is downloaded to a computer, and subsequent data analysis follows using a software system.
1. Insufficient acid suppression
2. Reflux hypersensitivity
3. Functional heartburn
4. Alternative diagnosis
The overall interpretation of the study is based on normal data obtained from healthy volunteers, which serve to establish reference values. Because acid-suppressive therapy alters the ratio of acid versus non-acid reflux episodes in the postprandial period and reduces the total number of reflux episodes, different normal values are utilized when interpreting the total number of reflux episodes “on” and “off” acid-suppressive therapy.
The symptom index and symptom association probability are two indices that help to assess the association of a patient’s symptoms with gastroesophageal reflux episodes (acid and non-acid). The symptom index measures the overall strength of the relationship between symptoms and reflux episodes, and the symptom association probability determines whether this relationship is due to chance.
1. Symptom index (SI): number of symptoms associated with reflux occurring in the preceding 5-minute interval divided by the total number of symptoms recorded by the patient during the monitoring period.
2. Symptom association probability (SAP): the total measuring time divides into two-minute intervals. A contingency table with four fields listed below assesses correlation with the Fisher exact test.
A positive SAP (greater than 95%) is considered statistically significant and is interpreted as an adequate temporal association between GER and the recorded symptom.
Although MII-pH testing is a great tool to assess and diagnose GERD-related symptoms, there are some limitations and drawbacks to the test.
Complications of MII-pH testing include bleeding, infection, and trauma to the nasopharynx or esophagus.
The procedure is relatively safe; however, the placement of a transnasal catheter may produce some nasopharyngeal discomfort. It may also alter the usual activities of a patient, including food and drink consumption. Despite this, patients are usually able to complete the entire 24-hour examination. Before the procedure, patients should receive counsel on expectations before the day of the examination, as well as how and what to log in a diary.
The contraindications for placement of a transnasal MII catheter include prior nasal surgery or trauma, concurrent use of anticoagulants, or coagulopathy. Safety data on the use of impedance in patients with implantable cardiac defibrillators and pacemakers are yet to be studied.
In conclusion, MII-pH is a helpful tool to diagnose GERD as it is more accurately able to detect the variances in refluxate composition at various pH levels than pH-metry alone. It has a high sensitivity in identifying all types of reflux episodes. This data collection allows the provider to be better equipped with information to personalize treatment for the patient depending on the underlying cause of their symptoms.
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