Under the concept of chronic atrophic gastritis (CAG) it is included any type of inflammation of the gastric mucosa where a cellular inflammatory infiltrate composed mostly of lymphocytes and plasma cells with very few neutrophils are identified. There are various classification systems based on the histological features and the degree of gastric atrophy, and also based on the predominant location, being type A primarily located in the gastric body whose etiology would be autoimmune; and type B, preferably located at the antrum that would have more relationship with Helicobacter pylori.
Type A gastritis is the less common form and is associated with pernicious anemia and the presence of circulating antibodies against parietal cells and intrinsic factor, hence the name of autoimmune gastritis. Such antibodies are found in over 90% of patients with pernicious anemia and up to 50% of patients with type A gastritis.
Autoantibodies anti-parietal cells and atrophic gastritis are identified in 20% of individuals over 60 years in relatives of patients with pernicious anemia. Thyroid disease is common in these patients, so that half of them have antibodies against thyroid antigens and about 30% of patients with thyroid disease have antibodies anti-parietal cells. Also there has been a significant incidence of specific haplotypes of familial histocompatibility as the HLA B8 and DR3.