Severe peptic ulcer diathesis secondary to gastric acid hypersecretion due to unregulated gastrin release from a non-β cell endocrine tumor (gastrinoma) defines the components of the ZES. Initially, ZES was typified by aggressive and refractory ulceration in which total gastrectomy provided the only chance for enhancing survival. Today ZES can be cured by surgical resection in up to 30% of patients.
Gastric acid hypersecretion is responsible for the signs and symptoms observed in patients with ZES. Peptic ulcer is the most common clinical manifestation, occurring in >90% of gastrinoma patients. Initial presentation and ulcer location (duodenal bulb) may be indistinguishable from common PUD. Clinical situations that should create suspicion of gastrinoma are ulcers in unusual locations (second part of the duodenum and beyond), ulcers refractory to standard medical therapy, ulcer recurrence after acid-reducing surgery, ulcers presenting with frank complications (bleeding, obstruction, and perforation), or ulcers in the absence of H. pylori or NSAID ingestion. Symptoms of esophageal origin are present in up to two-thirds of patients with ZES, with a spectrum ranging from mild esophagitis to frank ulceration with stricture and Barrett's mucosa.
Diarrhea is the next most common clinical manifestation, in up to 50% of patients. Although diarrhea often occurs concomitantly with acid peptic disease, it may also occur independent of an ulcer. Etiology of the diarrhea is multifactorial, resulting from marked volume overload to the small bowel, pancreatic enzyme inactivation by acid, and damage of the intestinal epithelial surface by acid. The epithelial damage can lead to a mild degree of maldigestion and malabsorption of nutrients. The diarrhea may also have a secretory component due to the direct stimulatory effect of gastrin on enterocytes or the cosecretion of additional hormones from the tumor, such as vasoactive intestinal peptide.
The first step in the evaluation of a patient suspected of having ZES is to obtain a fasting gastrin level. A list of clinical scenarios that should arouse suspicion regarding this diagnosis is shown in Table 274-5. Fasting gastrin levels are usually <150 pg/mL. Virtually all gastrinoma patients will have a gastrin level >150 to 200 pg/mL. Measurement of fasting gastrin should be repeated to confirm the clinical suspicion.
TABLE 274-5 When to Obtain a Fasting Serum Gastrin Level
Multiple ulcers Ulcers in unusual locations; associated with severe esophagitis; resistant to therapy with frequent recurrences; in the absence of NSAID ingestion or H. pylori infection Ulcer patients awaiting surgery Extensive family history for peptic ulcer disease Postoperative ulcer recurrence Basal hyperchlorhydria Unexplained diarrhea or steatorrhea Hypercalcemia Family history of pancreatic islet, pituitary, or parathyroid tumor Prominent gastric or duodenal folds
The next step in establishing a biochemical diagnosis of gastrinoma is to assess acid secretion. Nothing further needs to be done if decreased acid output is observed. In contrast, normal or elevated gastric acid output suggests a need for additional tests. Gastric acid analysis is performed by placing a nasogastric tube in the stomach and drawing samples at 15-min intervals for 1 h during unstimulated or basal state (BAO), followed by continued sampling after administration of intravenous pentagastrin (MAO). Up to 90% of gastrinoma patients may have a BAO of ≥15 meq/h (normal, <4 meq/h). Up to 12% of patients with common PUD may have comparable levels of acid secretion. A BAO/MAO ratio >0.6 is highly suggestive of ZES, but a ratio <0.6 does not exclude the diagnosis. Pentagastrin is no longer available in the United States, making measurement of MAO virtually impossible. If the technology for measuring gastric acid secretion is not available, a basal gastric pH ≥3 virtually excludes a gastrinoma.
Treatment of functional endocrine tumors is directed at ameliorating the signs and symptoms related to hormone overproduction, curative resection of the neoplasm, and attempts to control tumor growth in metastatic disease.
PPIs are the treatment of choice and have decreased the need for total gastrectomy. Initial doses of omeprazole or lansoprazole should be in the range of 60 mg/d. Dosing can be adjusted to achieve a BAO <10 meq/h (at the drug trough) in surgery-naive patients and to <5 meq/h in individuals who have previously undergone an acid-reducing operation. Although the somatostatin analogue has inhibitory effects on gastrin release from receptor-bearing tumors and inhibits gastric acid secretion to some extent, PPIs have the advantage of reducing parietal cell activity to a greater degree.
THE RECOMMENDED LITERATURE
1. Harrison's Principles of Internal Medicine 16th Edition
2. Short Textbook of Medical Diagnosis and Management (third edition)/ Moxammed Inam Danish.-Department of Medicine, Medical Unite III, Dow Medical College and Civil Hospital Karachi, Pakistan, 2007. – 580 p.
3. Davidson’s Principles and practice of medicine (nineteenth edition)/Christopher Haslett, dvin R. Chilvers and others. – Edinburgh, 2007. – 1276 p.
4. Kelley's essentials of internal medicine/ editor-in-chief H.D. Humes . ─ 2nd ed. ─ Philadelphia : Lippincott Williams & Wilking, 2011.
5. Brochetr, A. Internal medicine subspecialties/ A. Brochert . ─ Philadelphia : Hanley & Belfus, 2006
6. Khrenov A.A. Therapy: Manual.— Simferopol, 2007.— 444 p.
Teacher recommends more monographic and periodical literature.