Crohn's disease, an inflammatory bowel disease, can strike people of any age and can cause a diverse array of symptoms. Some patients suffer discomfort and inconvenience, while others suffer debilitating consequences and require repeated bowel surgeries. The complex nature of the disease hinders doctors who want to counsel their patients and scientists who want to improve treatments or find a cure. Experts developed a classification scheme to try to overcome the complexity of the disease by grouping together similar patients.
History
In 1998, a team of experts on Crohn's disease gathered in Vienna to devise a classification scheme to group together patients by shared disease characteristics, hoping that separate analysis of each group could clarify the development of symptoms and response to treatments. The result was the Vienna Classification system. After a few years of use, it became clear that refining the Vienna Classification criteria could provide better data. The experts met again in Montreal in 2005 to develop the "Montreal Modifications" to the Vienna system, which refined the age groups and the determination of sites affected by the disease.
Age Groups
The Vienna classification split patients into two age groups based on age at the time of diagnosis: 40 and under or over 40. When new data suggested that young patients have more severe disease, the experts in Montreal decided to split the under-40 age group to into a pediatric population of patients age 16 and under and another group aged 17 to 40. The Montreal modification retains the grouping of patients older than 40.
Patterns
The Merck Manual succinctly describes the three primary patterns or "behaviors" of Crohn's disease according to the Montreal modifications. From least to most severe, the patterns are B1, primarily inflammatory; B2, primarily obstructing; and B3, primarily penetrating. Patients with inflammatory disease experience frequent cramping and diarrhea but avoid the more serious complications, although inflammatory disease can evolve into the other types. Obstructing or stenotic disease narrows the diameter of the intestines, causing strictures that can block the smooth flow of digesting food and require surgery. Penetrating or fistulizing disease occurs when ulcers erode the walls of the intestines so that the digestive contents contaminate the body, which can be life-threatening.
Location
Crohn's disease primarily affects the ileum, the lowest part of the small intestines, but it can affect any segment of the digestive tract. In his June 2007 article in "Canadian Journal of Gastroenterology," Dr. Hugh Freeman outlines the disease locations according to the Montreal modifications: L1, ileum; L2, colon or large intestines; L3, their junction, the ileocolon; and L4, the upper gastrointestinal tract.
Significance
The classification of Crohn's disease into different groups based on patients' age, disease location and behavior suggests different treatment regimens and guides doctors to the best options for a particular patient. For example, according to Dr. Freeman's work, patients who are under 40 at the time of diagnosis have more severe and widespread disease than patients over 40, and they might benefit from more aggressive treatment options.
