Causes of decreased gastric acid production:
(1) gastric atrophy
(2) drug-induced acid suppression
(3) endocrine and metabolic
(4) other
Causes of gastric atrophy:
(1) age-related atrophy
(2) autoimmune gastritis
(2a) pernicious anemia (antiparietal cells antibodies)
(2b) with rheumatoid arthritis
(2c) with thyroid disease (hypothyroidism or hyperthyroidism)
(2d) with vitiligo
(3) other forms of chronic gastritis (which may be associated with gastric ulceration or gastric carcinoma)
(4) Menetrier's disease (hypertrophic gastritis)
Drug-induced acid suppression:
(1) H2 receptor blockers (cimetidine and ranitidine target the H2 receptor of parietal cells)
(2) proton pump inhibitors (opremazole, others)
(3) antacids
(4) buffering agents in drugs (such as with antiretroviral therapy)
(5) ganglion blocking agents
(6) prostaglandins and prostaglandin analogs (misoprostol)
(7) anticholinergic agents (atropine, pirenzepine, telenzepine)
(8) antagonists to the gastrin receptor on parietal cells (CCK2 receptor)
Endocrine:
(1) VIPoma (vasoactive intestinal peptide secreting carcinoid tumor), aka Pancreatic Cholera or watery diarrhea, hypokalemia, achlorhydria (WDHA) syndrome
(2) gastric inhibitory polypeptide (GIP) in response to hyperglycemia or other stimuli
(3) secretin
(4) somatostatin
(5) cholecystokinin
Other:
(1) HIV infection
(2) extensive gastric resection
(3) post-vagotomy
(4) diffuse gastric scarring after a toxic ingestion
