Diarrhea is a term used to describe a frequent passage of watery or unformed stool. Diarrhea is considered acute if it lasts up to 2 weeks, persistent – if it lasts for 2-4 weeks and chronic if it lasts longer than 4 weeks. Unlike acute diarrhea, chronic diarrhea usually is not infectious, although sometimes persistent infections may be the cause.
The amount of stool and its consistency depends on the balance between the fluid and minerals absorption and secretion in the intestines, basically one of the main functions of the small intestines and colon as this way our body maintains stable and healthy water-minerals balance in the body. Diarrhea develops as a result of an impaired balance between the absorption and secretion in the intestines, motility and sensory dysfunction of the gut via various mechanisms due to numerous different disorders such as irritable bowel syndrome, enzyme deficiencies, and some chronic infections.
Secretory diarrhea develops due to impaired fluid and electrolyte transport across the intestinal mucous membrane. In this case, watery diarrhea occurs and a large amount of feces. Usually, it is not associated with any pains and is present even when a person is fasting.
- Medications and toxins
Olmesartan, a drug used to treat hypertension and heart failure, is known to cause diarrhea. Exposure to some toxins such as arsenic is associated with chronic diarrhea. Regular use of laxatives is a cause of chronic diarrhea.
- Chronic alcohol consumption
Ethanol damages the intestinal cells and, therefore, leads to impaired sodium and water absorption and secretory diarrhea.
Some tumors such as gastrointestinal carcinoid tumors secrete hormones (serotonin, histamine, prostaglandins, kinins) which induce intestinal secretion and cause diarrhea. A specific tumor called gastrinoma produces gastrin, which may also lead to diarrhea in some people. Medullary carcinoma of the thyroid is associated with diarrhea due to the secretion of calcitonin and prostaglandins.
Corticosteroid deficiency (Addison’s disease) may also cause diarrhea.
- Congenital defects of mineral absorption
Some rare congenital disorders (congenital chlorodorrhea, congenital sodium diarrhea) cause abnormal electrolyte transport and, respectively, secretory diarrhea.
Osmotic diarrhea develops when some substances that are poorly absorbed drag the fluid into the intestine. The gut cannot reabsorb this amount of fluid and diarrhea occurs. Fasting usually stops diarrhea.
- Drugs – osmotic laxatives
Antacids which contain magnesium (commonly used to treat gastritis and lessen heartburn) may induce diarrhea.
- Carbohydrate malabsorption
Some enzyme deficiencies such as lactase deficiency, malabsorption of sorbitol and fructose also cause osmotic diarrhea.
- Wheat intolerance
Non-celiac gluten intolerance is associated with chronic diarrhea, bloating and abdominal pain.
Malabsorption of fats causes diarrhea with greasy bad-smelling stool. This happens due to the increased amount of undigested fat in the intestines that leads to osmosis and fluid retention in the lumen of the gut.
- Pancreatic insufficiency
Pancreas dysfunction due to chronic pancreatitis, cystic fibrosis, pancreatic duct obstruction is associated with maldigestions of fats and, therefore, usually causes diarrhea.
- Mucosal malabsorption
Some disorders like celiac disease, tropical sprue, and Whipple’s disease are characterized by the involvement of intestinal mucosa and nutrient malabsorption which in turn causes diarrhea.
Inflammation of the intestinal mucous membrane results in fluid exudation in the lumen of the gut causing diarrhea. Additionally, fat malabsorption, increased bowel motility, impaired fluids, and mineral absorption develop, which also contribute to diarrhea.
- Inflammatory bowel disease
Crohn’s disease and chronic ulcerative colitis are relatively common inflammatory diseases associated with diarrhea.
- Eosinophilic enteropathy
Eosinophils infiltrate the mucous membrane and disrupt the normal absorption.
- Other diseases such as certain immunodeficiencies, radiation enterocolitis, chronic graft-versus-host disease, Behçet’s syndrome, and Cronkhite-Canada syndrome.
Impaired bowel motility/functional diarrhea
Increased motility is a quite unusual cause of chronic diarrhea, although it is also possible.
- Irritable bowel syndrome
The condition is characterized by altered intestinal motility and inflammation of the mucosa – these factors contribute to diarrhea.
- Diabetic diarrhea
Diabetes damages the autonomic nervous system which regulates bowel motility and, respectively, leads to diarrhea.
Increased thyroid function may lead to hypermobility of the gut.
Chronic diarrhea consequences
Chronic diarrhea leads to fluids and mineral loss, protein and vitamin deficiencies. In general, the body’s immune system and wellbeing are affected as well as the person’s mental state.