The word metaplasia in simple terms refers to the change or transformation of a cell from one type to another type that is not normally present in the tissue. These cellular transformations are usually complete thus giving rise to a mature or differentiated cell type. It differs from transdifferentiation in that the cell type formed in transdifferentiation is also a resident in the tissue. With the increasing incidence of several forms of cancers and other health conditions, the word metaplasia is becoming commonplace.
Although similar, metaplasia differs in meaning from closely related words like dysplasia, hyperplasia, hypertrophy, and neoplasia. Dysplasia refers to an abnormality in the growth and or development of cells and or organs with a resultant abnormality in the histology (as seen under a microscope) or gross anatomy of the organ while neoplasia refers to a new, abnormal, and excessive growth of tissue structures which may be malignant or benign. Hyperplasia is the increase in the number or amount of cells as a result of increased cell proliferation and hypertrophy is the increase in the mass of single cells.
Mechanism of metaplasia
Cells undergo metaplastic changes when they are subjected to stress. This stress can be either physiological or pathological. These stresses can be physical or chemical. Physical stress can take the form of continued rubbing or abrasion of a body surface, increases pressure, etc. chemical stressors include smoke, nicotine, gastric acid, hormones, alcohol, pH change, infection, etc. whether the stress is physical or chemical, a common denominator underscores them – they must be chronically present. The chronicity of these stressors is what triggers the metaplastic change. This change occurs in a bid to adapt to the stress. Summarily, metaplasia occurs when in a bid to adapt to chronic stress, a cell changes or transforms to another cell type.
Types of metaplasia
Metaplasia can be physiological or pathological
- Physiological metaplasia: This type of metaplasia arises as part of a normal physiological response to development and cyclical hormonal changes. This implies that they do result from abnormalities, insults, or injuries to body cells. An example is squamous metaplasia that occurs in the cervix of the uterus during the menstrual cycle which results in the migration of the squamocolumnar junction and the conversion of fibrous tissue into the bone during development.
- Pathological metaplasia: Metaplasia becomes pathological when the change is brought about by an insult that disrupts the normal internal milieu of the cell. An example is intestinal metaplasia that is seen in the lower esophagus in people with gastroesophageal reflux disease (GERD).
Metaplasia can also be classified based on the type of change and area affected. These include:
- Squamous metaplasia: this type of metaplasia occurs when the original cells resident in the tissue change to squamous cells. It is implicated in lung cancers (where it can occur in the lung alveolar or the airway) and Human Papilloma Virus mediated squamous cell cancer. Squamous metaplasia can also occur in the breast in the background of chronic inflammation, abscess, and cysts.
- Acinar-ductal metaplasia: this occurs majorly in the pancreas. It has been observed to occur in the setting of chronic pancreatitis from where there is a possibility of progression to pancreatic cancer.
- Intestinal metaplasia: this is majorly seen in people with Barret’s esophagus (a consequence of longstanding Gastro-esophageal reflux disease) and is perhaps one of the main causes of concern to a large population of people. Here the cells lining the esophagus and stomach are replaced by goblet cells. These goblet cells are normally resident in the intestines but not in the stomach or the esophagus hence the name, intestinal metaplasia. It is considered a precancerous lesion and if left untreated, can result in adenocarcinoma of the lower esophagus (a form of cancer).
Causes of metaplasia
Following the high risks of cancerous transformation of metaplastic cells, it is important to note the possible etiological agents. These include but are not limited to:
- Hot beverage
- Smoked fish
- Processed carbohydrates
- Low residue or fiber diets
- Extreme changes in pH
- High salt intake
- Helicobacter pylori
- Environmental toxins like asbestos, silicon, secondhand smoke, etc.
- Acid reflux
Helicobacter Pylori infection which is implicated in the causation of peptic ulcers has been shown to have a causal relationship to intestinal metaplasia. How this occurs is however still being studied. There’s no conclusive data on whether certain foods can cause intestinal metaplasia. However, smoked foods increase the risk.
Risk factors for intestinal metaplasia
Across the globe, about 1 in 4 persons who have had an upper gastrointestinal endoscopy have intestinal metaplasia. The list below is not exhaustive but outlines some of the commonest risk factors for intestinal metaplasia:
- Chronic smoking
- Chronic secondhand smoking
- Peptic ulcer disease with Helicobacter Pylori
- Long-standing Gastro-esophageal reflux disease (GERD, Acid reflux)
- Family history of gastric cancer or adenocarcinoma of the esophagus in a first-degree relative
- Advanced age (the older the person, the higher the chances)
- Lack of Ascorbic acid (vitamin C) in the diet
- Chronic alcoholism
Symptoms of intestinal metaplasia
Most people with intestinal metaplasia are asymptomatic. Typically, symptoms start to present when malignant changes start to occur. However, depending on the stressor causing the metaplasia, certain symptoms may be noticed. These include acid reflux, heartburn, dyspepsia, waterbrash, and belching in gastro-esophageal reflux disease or abdominal pain, nausea, vomiting, and bloating in peptic ulcer (from H. pylori. Therefore, the symptom present depends on the underlying condition causing the metaplasia.
In most cases, intestinal metaplasia is an incidental finding while evaluating a patient for other health conditions. This occurs during an upper gastrointestinal endoscopy. This investigation method involves the insertion of a tube housing a camera through the mouth into the stomach to visualize the stomach and the esophagus. During this endoscopy, samples of the gastric and esophageal mucosa are also taken (biopsied) for histopathological examination in other to tentatively establish a diagnosis.
Depending on what is implicated as the etiologic agent, several treatment modalities can be employed.
- If caused by gastroesophageal reflux disease employ the following;
- Avoid going to bed immediately after meals or within 30 minutes of having a meal.
- When lying down, assume the elevated head end position by using a pillow.
- Avoidance of spicy food, acidic foods, and alcohol.
- Medication: Prilosec (omeprazole), Pepto Bismol (bismuth subsalicylate), Ranitidine
- If caused by Helicobacter Pylori, antibiotics therapy is the preferred mode of treatment. These antibiotics include amoxicillin, metronidazole, and clarithromycin. These antibiotics are to be taken for 2 weeks.
Preventive healthcare is the hallmark of 21st-century medical practice. The following will prevent or reduce the incidence of intestinal metaplasia:
- Eating foods rich in antioxidants like fresh fruits and leafy vegetables
- Eating a diet rich in fibers
- Eating a diet laden with fruits, vegetables, and nuts.
- Avoid processed food – eat whole grains.
- Reduce intake of foods rich in fat.
- Reduce spicy foods.
- Reduce salt intake in the diet.
Can metaplasia be reversed?
As stated at the beginning of this publication, metaplasia is a stress response. If these stressors are removed, the body will theoretically return to its pre-metaplastic state although there is not enough literature to support this. Hence, quitting smoking, treatment of GERD, and eradication of Helicobacter Pylori are the first steps towards reversal. Therefore, once a diagnosis of metaplasia is made, it will benefit the individual to adopt a positive lifestyle modification.
Helicobacter pylori can significantly increase the risk and rate of progression of intestinal metaplasia. Complete eradication of this bacteria coupled with treatment of GERD and quitting smoking are the first steps toward a good prognosis in its management.