The term gastritis refers to an inflammation of the stomach wall. The severity of inflammation caused by gastritis may vary on an individual basis. This causes some persons to experience painful symptoms, whereas others may not show any symptoms at all. Abdominal pain, nausea and vomiting are some of the symptoms that may occur with gastritis along with changes in appetite.
The stomach is a hollow organ. Therefore, the process of inflammation in gastritis is restricted to the walls of the stomach. In some cases, the inflammation is restricted to the superficial surface of the stomach wall, involving only the inner mucosal lining of the stomach. In other cases, the inflammation may be more extensive, and involve the entire thickness of the stomach wall. Chronic, persistent gastritis can lead to the formation of painful ulcers or sores in the wall of the stomach.
Inflammation of the stomach during gastritis can occur due to many different causes. The two most common causes of chronic gastritis in the human population are infection with the bacteria, Helicobacter pylori (commonly abbreviated as H. pylori), and long-term use of a class of painkiller drugs referred to as non-steroidal anti-inflammatory drugs (commonly abbreviated as NSAIDs).
Chronic alcoholism and injury may also cause gastritis. In some rare cases, the cause of gastritis may not be an external factor, but a faulty immune system causing inappropriate immune reactions. Such cases fall under the category of autoimmune gastritis. Once H.pylori infection and chronic NSAID use have been ruled out as potential causes of gastritis in an individual, autoimmune gastritis needs to be considered as a possible cause of stomach inflammation.
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What is autoimmune gastritis?
Autoimmune gastritis is caused by an inappropriate immune reaction of the body towards the components of the stomach tissue. It is a chronic condition that results in progressive atrophy and destruction of the stomach tissue. For this reason, autoimmune gastritis is also sometimes referred to as autoimmune metaplastic atropic gastritis or autoimmune atrophic gastritis.
Autoimmune gastritis causes a decrease in the amount of gastric acid secretion, a condition known as achlorhydria. It may also cause vitamin B12 deficiency, resulting in megaloblastic or pernicious anemia. In addition, autoimmune gastritis is also a risk factor for the development of gastric cancer. Therefore it should be taken very seriously even though it is not a common type of cancer.
What happens in autoimmune gastritis?
The first major steps in the digestion of food occur in the stomach. The walls of the stomach are comprised of three main types of cells: mucus cells, peptic cells, and parietal cells. In autoimmune gastritis, the immune system of the body inappropriately targets and destroys the parietal cells. The parietal cells are responsible for the production of hydrochloric acid (HCl) and intrinsic factor (abbreviated as IF).
Hydrochloric acid is a key component of the gastric juice, which also contains potassium chloride and sodium chloride. Hydrochloric acid produced in the stomach is a very strong acid (pH of approximately 1.5-3.5). It plays an important role in the digestion of food in the stomach. Hydrochloric acid helps in the breakdown of proteins in the food through activation of stomach enzymes and unraveling the protein structures. Hydrocholoric acid is also required for the absorption of vitamin B12.
These processes of digestion and absorption get affected in autoimmune gastritis. Ultimately, the other cells of the stomach wall also get destroyed in autoimmune gastritis. However, they are not targeted directly by the immune system. The adverse effects of autoimmune gastritis are caused by the production of auto-antibodies against the parietal cells of the stomach wall, the intrinsic factor, and the hydrogen-potassium ATPase proton pump. A class of T-cells known as the CD4+ T-cells are thought to be important in mediating the autoimmune response.
The auto-antibodies lead to a gradual yet extensive destruction of parietal cells, especially in the fundus and body of the stomach. The inflammation, atrophy and destruction of parietal cells may affect the entire stomach in some cases. In other cases, the damage may be restricted to certain patches on the mucosa of the stomach. When the destruction of the stomach tissue occurs in a patchy manner, the isolated normal regions of the gastric mucosa appear as polyps (also known as pseudopolyps).
Parietal cell destruction in autoimmune gastritis leads to a decrease in the production of gastric acid. This stimulates a feedback loop that leads to increased production and secretion of the hormone, gastrin, in an effort to increase gastric acid production. Gastrin stimulates parietal cells and enterochromaffin-like cells. In fact, increased gastrin levels lead to hyperplasia of the enterochromaffin-like cells. Abnormal cellular changes may also be seen in the regions of the stomach that undergo atrophy.
Signs and Symptoms
The clinical signs and symptoms of autoimmune gastritis are mostly attributed to vitamin B12 deficiency and pernicious anemia. Although lowered production of gastric acid in autoimmune gastritis may have an effect on the proper digestion of food, no significant signs and symptoms develop due to lowered gastric acid production (unless large portions of the stomach wall are affected).
Even the signs and symptoms of vitamin B12 deficiency and pernicious anemia develop gradually over a period of decades. The following are some of the signs and symptoms associated with autoimmune gastritis:
- Numbness and paresthesia (abnormal sensations) may develop in the legs.
- Weakness may develop in the limbs.
- Diarrhea may occur.
- Cracks appear at the corner of the lips.
- Stomatodynia or mouth pain may occur.
- Depression, malaise, poor memory and mild personality changes may occur.
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Causes of Autoimmune Gastritis
Due to the hereditary nature of autoimmune gastritis, the main cause of this disease is thought to be a fault in the genes. However, the exact genes responsible for autoimmune gastritis are not yet known. Autoimmune gastritis is also associated with several other hereditary disorders, such as type I diabetes, primary hypoparathyroidism, Addison’s disease, myasthenia gravis, Graves’ disease, and Lambert-Eaton syndrome.
Long-term infection with the bacteria, Helicobacter pylori, is also associated with this condition. However, the mechanism of this link is not understood. Other conditions that may be potential causes of autoimmune gastritis include surgical removal of some parts of the stomach (technically known as gastrectomy) and chronic use of a class of antacid drugs known as proton pump inhibitors.