Crohn’s disease is a type of inflammatory bowel disease (IBD) characterized by chronic inflammation that can affect any part of the digestive tract, from the mouth to the anus. This inflammation is transmural, meaning it extends through all layers of the bowel wall, distinguishing it from other inflammatory conditions. When Crohn’s disease remains untreated, this persistent inflammation is a progressive process that results in cumulative, irreversible damage to the gastrointestinal system and has widespread effects on the rest of the body. The natural history of the disease involves a shift from primarily inflammatory symptoms to the development of structural complications over time, underscoring the need for continuous medical management to halt this progression.
Structural Damage to the Gastrointestinal Tract
The chronic, deep inflammation associated with untreated Crohn’s disease progressively damages the intestinal wall, often leading to three major localized complications: strictures, fistulas, and abscesses. As the body attempts to heal the deep ulcers caused by the disease, scar tissue builds up in a process called fibrosis, which is a dysfunctional attempt at repair. This accumulation of scar tissue and thickening of the bowel wall results in the formation of a stricture, which is a segment of the intestine that has become abnormally narrowed.
Strictures impede the normal passage of food and waste through the digestive tract, which can cause significant symptoms like severe cramping and vomiting. A stricture may initially be caused by swelling and inflammation, but over time, it becomes fixed and rigid due to the scar tissue, making it a permanent obstruction that often requires surgical intervention. The persistent inflammation can also penetrate through the entire thickness of the weakened bowel wall, creating an abnormal tunnel known as a fistula.
Fistulas can connect different loops of the intestine to one another, or they can tunnel from the intestine to other organs like the bladder, the vagina, or the skin surface. These tunnels divert the contents of the bowel to places they should not be, leading to chronic infection and drainage. Furthermore, the deep ulceration and penetrating inflammation can cause localized pockets of infection and pus to form, which are referred to as abscesses. Abscesses often form near the site of fistulas or strictures and can cause high fever and severe localized pain, requiring immediate drainage and antibiotic treatment.
Body-Wide Nutritional and Inflammatory Effects
Beyond the direct damage to the gut structure, untreated Crohn’s disease triggers systemic consequences that affect overall body health, primarily through chronic inflammation and malabsorption. The inflammation in the digestive tract hinders the small intestine’s ability to properly break down and absorb nutrients, a condition known as malabsorption. This often leads to significant malnutrition and unintended weight loss. Patients may also limit their food intake due to pain or fear of triggering diarrhea.
Nutritional Deficiencies
Deficiencies in specific micronutrients are common, including fat-soluble vitamins like Vitamin D and Vitamin K, and water-soluble vitamins such as Vitamin B12, particularly when the terminal ileum is affected. Iron deficiency is also frequent because of chronic, slow blood loss from intestinal ulcers and poor absorption of iron. This combination of factors often results in anemia, characterized by a lack of healthy red blood cells, which contributes to profound fatigue.
Extra-Intestinal Manifestations
The body’s immune response, which drives the intestinal inflammation, does not always stay confined to the digestive tract, leading to extra-intestinal manifestations (EIMs). Systemic inflammation can cause issues in distant parts of the body, such as the joints, where it can manifest as arthritis or joint pain. Other EIMs include inflammatory conditions of the eyes, such as uveitis, and skin disorders like erythema nodosum, which presents as painful, tender red nodules. The chronic inflammatory state also elevates the long-term risk for developing colorectal cancer after many years of active disease.
Life-Threatening Acute Events
The structural damage that progresses when Crohn’s disease is left untreated can eventually culminate in acute, life-threatening medical emergencies. One of the most common severe outcomes is a complete bowel obstruction, where the narrowed segment of the intestine from a stricture blocks the passage of stool and gas entirely. This blockage leads to intense cramping, abdominal distension, and persistent vomiting, and requires immediate hospitalization to relieve the pressure and prevent intestinal tissue death.
Perforation occurs when a deep ulcer or a severely weakened portion of the bowel wall tears open, spilling the contents of the intestine into the sterile abdominal cavity. This event causes peritonitis, a widespread and severe infection of the abdominal lining that is a surgical emergency with a high risk of mortality.
Another immediate danger is a severe gastrointestinal hemorrhage, or significant bleeding, which stems from the deep, untreated ulcerations eroding into major blood vessels. While mild bleeding is common, life-threatening hemorrhage is an extremely serious complication that can lead to hemorrhagic shock and requires urgent intervention, often involving blood transfusions and emergency surgery to stop the blood loss.