Celiac disease can also be called gluten-induced enteropathy. This simply means that there is damage to the intestines (enteropathy) in susceptible individuals that is caused by eating gluten.
The damage in CD is usually found only in the small intestine. It begins at the part of the small intestine closest to the stomach, called the duodenum. With time, it progresses farther down involving the entire small intestine. It may even involve the stomach and large intestine, although this is unusual.
Biopsies are the definitive test in determining is someone has CD. The biopsies are almost always done endoscopically, which means the doctor, usually a gastroenterology specialist, will put a tube down the throat and pass it through the stomach to the small intestine. Little tiny scissors-like instruments are used to take small amounts of tissue. The ideal place to do the biopsies is in the small intestine, which is where celiac disease begins. The recommended area is usually the second part of the duodenum. Multiple spots must be biopsied, usually selected at random.
A pathologist will then look at the biopsies. He or she will be looking at the lining cells of small intestine, especially the appearance of the villi. The villi of the intestinal lining cells are projections of the cells into the inside of the intestine. This is where food and other nutrients are absorbed. People with celiac disease who eat gluten will have progressive damage to the villi, as they get flatter, and eventually the cells become completely flat without villi. Other changes include the grouping of white blood cells in the area, as well as inflammation in areas called crypts.
A good pathologist will know how to appropriately view and interpret the specimens. He or she will be able to say if there is evidence of enteropathy in the biopsy tissue. There are also degrees of abnormalities. These are often given what are called Marsh Grades 0 to 4, and higher degrees of abnormality usually go along with more intestinal symptoms.
There are other diseases that can cause these changes, but usually can be eliminated as possibilities by the history of the person’s illness. Tropical sprue, for example, may look like CD on biopsy but is caused by a bacterial infection in people visiting or living in the tropics.
The diagnosis of celiac disease involves a number of steps. It can be made in a person that has classic symptoms of celiac disease, or other diseases known to be related to CD as well as positive blood tests along with biopsied tissue that has the appearance of CD. In this case, a gluten-free diet is prescribed. If the person improves on a gluten-free diet, that is enough to make the diagnosis. Symptoms should improve, vitamin and other deficiencies should be corrected and antibody tests should eventually become negative.
It used to be thought that a second set of biopsies needed to be taken to show that the intestinal appearance was normal after a period of time on the gluten-free diet. Most doctors now do not consider that necessary and if there is a clear improvement in the patient’s condition once eating a gluten free diet then that is what confirms the initial diagnosis.