Gastrointestinal

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Peter Hollett and Ford Bursey Introduction

A wide variety of nuclear medicine examinations are available for studying the function of the gastrointestinal tract. Tests include assessment of salivary gland function; motility studies of the esophagus, stomach, small and large bowel; measuring substrate absorption; localization of gastrointestinal bleeding; detection of Meckel's diverticulum (covered in Chapter 17) and tests for inflammatory bowel disease (covered in Chapter 12). This Chapter is not meant to be exhaustive but rather will concentrate on some of the more important and commonly requested tests.

Clinical Role in Esophageal Motility Disorders

The esophagus must transport swallowed material from the mouth to the stomach while minimizing reflux of stomach contents. Symptoms associated with impaired function are dysphagia, pain or regurgitation. Motility disorders can be primary or secondary (Table 1) and result from smooth muscle disorders (e.g., scleroderma) or disorganization of the intrinsic nervous system (e.g., achalasia, Chagas' disease, and diabetes). The identification of these disorders can be aided by nuclear esoph-ageal motility studies though classification is still conventionally described in relation to esophageal manometry:

Normal: After a swallow, pressure in the upper esophageal sphincter (UES) and lower esophageal sphincter (LES) falls. A contraction wave starts in the pharynx and progresses down the esophagus.

Scleroderma: The lower part of the esophagus (smooth muscle) shows a reduced amplitude of contractions with hypotension of the LES.

Achalasia: The LES is usually hypertensive and fails to relax in response to a swallow. The body of the esophagus shows contractions that are reduced in amplitude and simultaneous in onset.

Diffuse esophageal spasm (DES): The lower part of the esophagus shows simultaneous-onset, large-amplitude, prolonged, repetitive contractions.

Hypercontractile esophagus ('nutcracker esophagus'): The major dysfunction is abnormal increase of contraction amplitude and normal propagation through the esophagus.

Non-specific motility disorder: Abnormalities that do not conform to any of the preceding patterns.

Technical Considerations

Most laboratories perform esophageal motility assessments with a liquid bolus, although some groups have claimed that semisolid materials are more sensitive. If

Nuclear Medicine, edited by William D. Leslie and I. David Greenberg. ©2003 Landes Bioscience.

Table 1. Esophageal motility disorders

Primary motility disorders Achalasia

Diffuse esophageal spasm Nutcracker esophagus Nonspecific motility disorder Presbyesophagus Secondary motility disorders

Collagen vascular disease (esp. scleroderma)

Esophagitis (reflux, caustic, medication, infectious)

Radiation injury

Alcoholism

Diabetes mellitus

Thyroid disease

Neuromuscular disorders esophageal and stomach motility are to be evaluated together then a radiolabeled solid meal or resin is often used. To avoid any interference with material already within the stomach, patients are typically asked to fast for at least six hours prior to the procedure. Care should be taken to note medications that affect esophageal function. For example, some prokinetic drugs can increase pressure in the LES or increase the amplitude of the peristaltic waves in those with gastroesophageal reflux disease (GERD). Anticholinergic drugs, nitrates and calcium channel blockers may lessen the pressure in the LES and predispose to reflux. Otherwise, it is uncommon for medications to induce clinically significant disorders of esophageal motility.

Gravity aids the passage of material through the esophagus in the upright position. Therefore, most examinations are performed in the supine position to isolate the effect of esophageal peristalsis. The patient is placed either in the prone or supine position under a gamma camera. After a practice swallow, the test bolus (usually 99mTc-sulfur colloid 20 MBq) is introduced and dynamic imaging is commenced at a frame rate of 1 s/frame for 2 minutes. The patient is asked to "dry" swallow every 15 seconds.

There are two scintigraphic approaches to measuring esophageal motility (Fig. 1). In the first, regions of interest (ROIs) are placed over the upper, middle, and lower thirds of the esophagus as well as the entire esophagus and transit is measured through these segments after a single swallow. The second approach measures residual activity in the esophagus after several dry swallows. High residual activity implies abnormal esophageal motility. This approach has the advantage of averaging the emptying of the esophagus over several swallows and is therefore less influenced by the occasional aberrant swallow. For both techniques, it is essential to avoid including stomach in the ROI as this can lead to erroneous results. Visual review of the data set in a cine display is also helpful.

Clinical

Impaired swallowing, or dysphagia, may occur because of a wide variety of structural or functional conditions, including stroke, cancer, neurologic disease and GERD. An esophageal motility disorder should be considered in anyone who has dysphagia

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