594 Lewin, Weinstein, and Riddell s Gastrointestinal Pathology and Its Clinical Implications

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1 594 Lewin, Weinstein, and Riddell s Gastrointestinal Pathology and Its Clinical Implications Figure Stages in the natural history of H. pylori. Biopsies from the antrum are on the left and the oxyntic mucosa on the right. A,B: Initial infection affects the antrum with minimal involvement of the oxyntic mucosa. C,D: Over time this extends to the oxyntic mucosa so that there is superficial inflammation but no atrophy. E,F: Ultimately the chronic inflammation extends into the specialized mucosa with gland loss. (This can also be exaggerated or mimicked with long-term PPI use.)

2 Chapter 13 Stomach and Proximal Duodenum: Inflammatory and Miscellaneous Disorders 595 Figure (Continued) G,H: Finally the oxyntic mucosa becomes lost completely and is replaced by pseudopyloric metaplasia, as shown here (invariably with endocrine cell hyperplasia), or with intestinal mucosa. The inflammation in the antral mucosa varies from virtually none when there is severe hypochlorhydria to modest if there is still sufficient acid secretion to support antral organisms (which require acid to prevent their urease causing too alkaline an environment). gastric metaplasia patches of gastric type mucous cells interspersed between the absorptive and goblet cells of the duodenal epithelium. Helicobacter pylori, when present in the duodenum, can only be identified in areas with gastric metaplasia. It is hypothesized that in the duodenum, similar to the gastric mucosa proper, H. pylori induces inflammation and erosions where it resides gastric metaplasia (and heterotopia) patches, 145 although in our experience this has a low yield (see subsequent section on duodenal disease). As such, the prevalence of duodenal gastric metaplasia is much lower in healthy volunteers. 145 ADVANCED H. PYLORI INFECTION: With sustained H. pylori infection, there is a gradual reduction of acid-producing mucosa because of gradual proximal spread of inflammation that facilitates H. pylori s proximal migration. Helicobacter pylori colonization is accompanied by the inflammation. As there is a gradual reduction in the acid-producing mucosa, the inflammatory front advances proximally with disease progression (Fig B). The development of hypochlorhydria and even achlorhydria, including use of PPIs, facilitates proximal migration of the bacteria, which allows the development of corpus gastritis, and eventually corpus atrophy (Fig C,D). This is the setting in which gastric ulcer and later gastric carcinoma develops (see Fig. 13-1). The natural history of H. pylori gastritis is for the inflammation to progress diffusely from the antrum into the adjacent corpus resulting in an atrophic front of advancing corpus injury (that may be visible endoscopically to the trained eye Fig ), leading to a reduction in acid secretion and eventually loss of parietal cells and development of corpus atrophy. 120,149,150 The front progresses uniformly and so appears to advance faster on the lesser curve (Fig ). This scenario is accelerated in clinical situations associated with low acid secretion such as chronic therapy with PPIs widely used in gastroesophageal reflux disease (GERD) (Fig ). Thus, antral-predominant gastritis may in some instances represent an earlier stage of atrophic pangastritis, these patterns representing two ends of the spectrum of H. pylori infection rather than mutually exclusive diseases. 14,120,154 H. pylori diagnosis. Depending on endoscopy need, diagnostic testing for H. pylori can be divided into invasive and noninvasive methods. 155 Noninvasive methods do not require endoscopy and include serology and urea breath test. Invasive tests require endoscopy; this group includes tests for urease, histology, and culture. The choice of test depends on the clinical situation (e.g., patient requires evaluation with upper endoscopy) and on other issues such as cost, availability, population prevalence of infection, pretest probability of infection, and factors such as the use of PPIs and antibiotics, which may influence certain test results. Noninvasive methods 1. Serology: Antibodies to IgG and IgA have been used successfully to study the epidemiology of H. pylori in different populations in different parts of the world. However, serology remains positive long after successful treatment of the infection and cannot be used to assess treatment outcome. Chapter 13

3 596 Lewin, Weinstein, and Riddell s Gastrointestinal Pathology and Its Clinical Implications Figure Left panel shows the natural and indistinct transition from antral oxyntic mucosa. That on the right shows the atrophic front (arrow). Prior to the rediscovery of H. pylori, this was thought to be an aging change. (Courtesy of Dr. Taiji Akamatsu.) Serologic tests are often species specific (H. pylori) and can be negative with infection with other Helicobacter species, for example, Helicobacter heilmannii. In addition, inaccurate tests are also more common in the elderly and in patients with cirrhosis in whom specificity can be compromised. As a result, other techniques are preferred in these settings Figure Advancing gastritis with time. A depicts Helicobacter-inflamed antrum and B Helicobacter-inflamed or possibly normal corpus/oxyntic mucosa. 1. No atrophy. 2. Atrophy is thought to begin at the junction of the antral corpus junction and spreads proximally in a cone-like manner. Often this equates with the angulus but the histologic junction is variable. 3. With time the cone extends proximally, but 4. Because the lesser curve is much shorter than the greater curve, the lesser curve is completely atrophic long before the greater curve and fundus. It is therefore possible to have biopsies from the lesser curve with complete atrophy and metaplasia but relatively normal oxyntic mucosa on the greater curve. 2. Urea breath tests, with 13 C or more widely available 14 C, provide a powerful, noninvasive tool for research. The principle is that the carbon-labeled urea is hydrolyzed by the urease in the H. pylori, if present, resulting in the formation of ammonia and carbon dioxide. The amount of labeled carbon dioxide in the breath is then measured. 159 The urea breath test provides an accurate assessment of H. pylori status that rivals histology for being the gold standard, 159 but can be negative in cases with a very low level of infection. 3. Stool antigen: The presence of H. pylori in the stool of infected patients has led to the development of fecal assays The stool assay shares a limitation of tests that use urease as a marker for the organism. 163,164 Though this is a noninvasive method, any of us who has been asked for a stool specimen might sympathize with its difficulty. Invasive methods 1. Rapid urease test is based on the organism s urease activity. It can be used at the bedside in the endoscopy unit. A gastric biopsy specimen is placed in contact with a pellet or solution that contains urea and a ph color indicator. The color changes when the ph rises above 6.0 as a result of hydrolysis of urea to ammonia Culture: Although culture is the theoretical gold standard as there is an excellent correlation with histologic identification, in practice and in many research studies, histologic identification is used as the gold standard. One reason is that in many

4 Chapter 13 Stomach and Proximal Duodenum: Inflammatory and Miscellaneous Disorders 597 Figure Oxyntic mucosa before and after a 2-week course of PPIs in a Helicobacter-positive patient. The increase in chronic inflammation over this time frame is readily apparent. laboratories, cultures are less frequently positive than histology and serology. This may be due to the fact that small numbers of organisms cannot always be cultured or identified, and also because there is varying expertise in different laboratories for culturing these organisms. In general, H. pylori is a fastidious and slow-growing organism that is difficult to culture Histology is currently considered the gold standard for detecting the infection for both untreated individuals and following therapy. The advantages of histology include the ability to document H. pylori infection, the degree of inflammation, and any associated pathology such as intestinal metaplasia, cancer, or lymphoma. The detection of organisms is enhanced by using special staining techniques discussed subsequently with their pros and cons in different clinical scenarios (see Table 13-9). What are we looking for and where? Helicobacter pylori is a small (3 0.5 mm), gram-negative, wavy rod-shaped bacteria. The organisms can be visualized on the luminal side of gastric surface and pit mucous cells, in or near the adherent mucous. Often the organisms seem to cluster near more normal-appearing mucous cells (Fig ) rather than near those exhibiting severe mucous depletion. A similar situation applies when H. pylori is associated with erosive gastritis. That is, the organisms do not overlie the erosion or the very reactive mucosa immediately adjacent to it; rather, they are present in adjacent, less abnormal mucosa. Also, as discussed in the subsequent section on duodenitis, H. pylori can sometimes be seen in the duodenum only in association with gastric surface cell metaplasia. Although we look for its characteristic shape, only a small proportion of organisms are in the plane of section and so have the characteristic shape. Hematoxylin and Eosin: Few studies report the accuracy of an H&E stain, 167,168 and it varies with the type of stain used. Experienced pathologists overall will have higher accuracy than junior pathologists in evaluating H&E-stained slides. 168 Even the staining intensity varies among biopsies within a given laboratory even in the same batch, and they are especially difficult to see if all are adherent to the epithelium. Nonetheless, within and between biopsy specimens there is often considerable variation in the numbers of organisms. H&E-stained slides have low sensitivity, in particular, in biopsies with low bacterial density. 168 This is particularly observed in patients using PPIs, in patients who recently received antibiotics, but also if biopsies are only taken from one part of the stomach instead of both antrum and oxyntic mucosa. Typically, there is chronic inflammation, but few or rare H. pylori organisms, and minimal or no active inflammation. It is also important to remember that studies evaluating H&E stains are not evaluating the same stain. Though H&E stain is the most widely used stain in medical diagnosis, there are a large number of H&E protocols. Primary differences are dye composition, staining protocol, and intensity of the blue dye. Staining contrast (including H. pylori) differ depending upon the approach that is used. For example, there are actually two very closely related compounds commonly referred to as eosin. Eosin Y (also known as eosin Y ws or eosin yellowish) that is the most often used, and has a slightly yellowish cast. The other eosin compound is eosin B (eosin bluish or imperial Chapter 13

5 598 Lewin, Weinstein, and Riddell s Gastrointestinal Pathology and Its Clinical Implications Figure A: Detail (high dry) view of H. pylori organisms at the entrance of a gastric pit. With a little experience, they can be recognized (as gray-blue) in conventionally stained sections. B: Higher-power ( 600) view showing the organisms more clearly with a modified Giemsa stain. red) and has a faint bluish cast. The two dyes are interchangeable, and selection of a particular eosin (or H&E protocol) is more a matter of preference and tradition. Overall, evaluating sections stained only with H&E leads to inconsistent results and special stains have been recommended whenever inflammation is present and organisms are not readily identifiable on an H&E stain. 13 However, if organisms are clearly identified on H&E stain in the presence of a compatible inflammatory infiltrate, this is usually adequate for diagnostic purposes. A useful rule of thumb is that, for any diagnosis of H. pylori, you have to be able to photograph it and stand up in court and defend the diagnosis. If this cannot be done, then a special stain is needed. Deciding when to order a special stain is itself fraught with problems, and such a pragmatic approach leads to underdiagnosing Helicobacter infection about 10% of the time when a decision is made on whether sufficient inflammation is present to justify ordering the special stain. Overall, pathologists do not appreciate how little inflammation may be seen in some biopsies with Helicobacter (see Fig ). While one could argue that if there is little inflammation, then the chances of that organism producing complications are small. This may not hold true if, for example, only antral biopsies are obtained showing only scant inflammation and no Helicobacter, as these may be ravaging the oxyntic mucosa. Policies for Detecting Helicobacter There is no correct protocol for histologic diagnosis of Helicobacter, and it depends on numerous factors that can be the driving force including the following: 1. The likelihood of organisms being present. In some populations, the positive rate is 10% to 20%, and in other >80%. In some commercial labs, it may even be supplier dependent; for an endoscopy group, serving a Western-white population may have an incidence that is <10%, whereas one serving, for example, a primary immigrant population from high Helicobacter prevalence areas, may have a rate in excess of 90%. 2. Commitment to turn-around time (TAT). Even though the vast majority of biopsies really are nonurgent, if a lab is committed to, for example, a 24-hour TAT, then this becomes the driving force. and an H&E and good special stain (silver or immunostain) may be done routinely. While in some biopsies the organisms may be easily visible at a first glance, opinions on how much time should one spend on one biopsy hunting for the organisms on H&E stain may vary when these are not that readily visible. This also gets into the issues of resource utilization and individual ego, where some take extra pride in their ability to find the organisms on H&E stain only and saving money (for the patient or institution). However, if the biopsies are normal, or the organisms are overtly detectable on the H&E stain, one can raise an ethical question of justification to bill for tests that were not really required. Unfortunately while opinions are many, evidencebased guidelines are lacking.