Types of Gastritis
Gastritis is primarily classified into two major etiologic types based on the underlying cause: H. pylori-associated atrophic gastritis (HpAG) and autoimmune gastritis (AIG), with HpAG being by far the most common. 1
Major Classification Systems
Primary Etiologic Classification
The 2021 AGA guidelines emphasize a pathogenesis-based approach that distinguishes gastritis by its primary trigger 1:
1. H. pylori-Associated Atrophic Gastritis (HpAG)
- Most common type of chronic gastritis
- Begins in the antrum and incisura, then progresses proximally to involve the corpus/fundus over time
- Characterized by multifocal atrophy that spreads along the lesser curvature
- Risk factors include age, tobacco use, high-salt diet, and possibly chronic bile acid reflux 1
- Prevalence up to 15% in US populations, higher in non-White racial/ethnic minorities and immigrants from high-risk countries 1
- The rate ratio of atrophic gastritis incidence is 5.0 times higher in H. pylori-infected vs. uninfected individuals 1
2. Autoimmune Gastritis (AIG)
- Significantly less common than HpAG (prevalence 0.5-2%) 1
- Characterized by corpus-predominant atrophy with antral sparing - this distribution pattern is the key distinguishing feature 1
- Caused by autoantibodies against parietal cells and intrinsic factor, plus T-cell-mediated destruction of oxyntic mucosa 1
- More common in women and increases with age 1
- Associated with other autoimmune diseases (up to one-third of patients with autoimmune thyroid disease have AIG) 1
- Can progress to pernicious anemia (prevalence 0.15-1%), a late-stage complication with vitamin B-12 deficiency 1
3. Chemical/Reactive Gastritis (Type C)
- Caused by bile reflux, NSAIDs, or other chemical/mechanical/toxic influences 2
- Mainly found in gastric remnants after partial resection 3
Historical ABC Classification (Less Emphasized Currently)
Older literature described 4, 3, 2:
- Type A: Diffuse atrophic corporal (autoimmune)
- Type B: Diffuse antral (H. pylori-associated)
- Type AB: Multifocal atrophic
- Type C: Chemical/reactive
However, this classification has been largely superseded by the etiologic approach emphasizing H. pylori vs. autoimmune pathogenesis.
Histopathologic Subtypes
Atrophic gastritis is defined as loss of gastric glands, with or without metaplasia, in the setting of chronic inflammation 1:
- Nonmetaplastic atrophy: Replacement with connective tissue
- Metaplastic atrophy: Replacement with intestinal metaplasia (IM) or pseudopyloric metaplasia 1
Critical clinical point: The presence of intestinal metaplasia on gastric histology almost invariably implies underlying atrophic gastritis, even if not explicitly stated in pathology reports 1.
Risk Stratification Systems
Two classification systems assess cancer risk based on severity and distribution 1:
- OLGA (Operative Link for Gastritis Assessment)
- OLGIM (Operative Link for Gastric Intestinal Metaplasia Assessment)
Both incorporate the topographic distribution and severity of atrophic lesions to stratify gastric cancer risk.
Clinical Significance and Cancer Risk
Both HpAG and AIG carry increased gastric cancer risk 1:
- Progression to gastric adenocarcinoma: 0.1-0.3% per year (similar to Barrett's esophagus or low-risk colorectal adenomas)
- Pernicious anemia patients have 7-fold higher relative risk of gastric cancer 1
- AIG patients have increased risk of type I neuroendocrine tumors (incidence 0.4-0.7% per year) due to hypergastrinemia from parietal cell loss 1
Common Pitfalls
- Underdiagnosis: Atrophic gastritis is often asymptomatic and inconsistently reported on histopathology 1
- Overlap between types: Molecular mimicry between H. pylori antigens and gastric H+/K+ ATPase may trigger AIG; if antral atrophy is seen in AIG, consider concomitant HpAG 1
- Biopsy technique matters: Proper diagnosis requires corpus and antrum biopsies placed in separate jars to distinguish distribution patterns 1