Familial Adenomatous Polyposis Health Article

Diagnosis

FAP can be diagnosed clinically in any individual with greater than 100 polyps in the colon or rectum. The diagnosis is usually made via flexible sigmoidoscopy. This procedure may be done on a routine basis or to investigate possible symptoms of colon polyps and/or colorectal cancer. Flexible sigmoidoscopy involves inspecting the interior of the rectum and the sigmoid colon, or the terminal part of the colon that leads to the rectum. Once polyposis has been established, complete colonoscopy may be necessary to further evaluate the extent of the polyps. Colonoscopy is a more invasive procedure that examines the interior of the entire colon and rectum, rather than only the terminal part.

In regards to a diagnosis in someone who does not yet have colon polyps, retinoscopy, or examination of the retina, can be useful in a family where CHRPE has been associated with FAP. In these families, CHRPE is almost 100% predictive of FAP; thus, if someone shows CHRPE on an ophthalmology exam, it is very likely that he or she is affected with FAP. Although genetic testing yields more certain predictive information, retinoscopy is a relatively inexpensive and noninvasive alternative diagnostic screening measure in families with a history of FAP associated with CHRPE.

Polyps may be first detected by the passage of occult (non-visible) blood in the stool by means of fecal occult blood testing. This testing is also inexpensive and noninvasive, and if positive, could indicate that additional testing is needed.

FAP can also be diagnosed by genetic testing. This type of testing may be used to identify someone who is affected but does not yet show any symptoms of FAP. It can also confirm the diagnosis of FAP in someone who has polyposis discovered via flexible sigmoidoscopy. APC gene testing is most commonly performed by using a protein truncation test, which looks for the presence of shortened proteins caused by a mutation in the gene. This test identifies approximately 80% of those affected with FAP. The other 20% of patients likely have mutations that do not lead to a shortened protein. It is important to test an affected family member first to determine whether or not a detectable mutation is present. If a mutation is identified in this affected person, other at-risk family members can be tested for this particular mutation. However, if a mutation is not identified in the affected individual, it is likely that the mutation does not produce a shortened protein. In this case, protein truncation testing would not be informative for the rest of the family.

FAP can also be diagnosed by linkage analysis. This testing identifies approximately 95% of affected individuals, however, blood samples are required from numerous family members, including at least one affected individual. Thus, logistically, this procedure is more complicated than the protein truncation testing mentioned above.

Treatment and management

There is no treatment for FAP because the genetic abnormality cannot be fixed. Management focuses on routine surveillance of at-risk and affected individuals for early detection and treatment of colonic polyps and other manifestations.

For individuals diagnosed with FAP, either clinically or via linkage analysis or protein truncation testing, an annual sigmoidoscopy must be performed beginning around the age of 10 years. Sigmoidoscopy is preferred because it is less invasive, safer, and will generally detect the polyps in FAP, since they are numerous and located throughout the colon. Colonoscopy may be the screening tool of choice if attenuated FAP is suspected since, in this case, the adenomas are fewer in number and may be confined to the proximal region of the colon.

If polyposis is established, complete colonoscopy may be necessary to determine the extent of the polyposis and the timing of surgery. As for surgical intervention, total proctocolectomy (removal of the colon and rectum) is generally favored. In some cases, however, other options may be explored, such as total colectomy (removal of the colon only) with ileorectal anastomosis (the small intestine is attached to the upper portion of the rectum). Another option, a total colectomy with rectal mucosal protectomy and ileoanal anastomosis, involves removing the entire colon and mucosal lining of the rectum. The ileum then attaches to the anus. Fecal continence is preserved since the muscular wall and the sensory functions of the rectum are preserved.

All FAP patients require an annual medical examination with palpation of the thyroid and review of systems. Children with FAP should be screened for hepatoblastoma with liver palpation. In some cases, hepatic ultrasonography and determination of serum alpha-feto-protein levels can be helpful as well. Upper endoscopy (visual examination of the upper GI tract) should be completed every one to four years to evaluate for gastric and duodenal polyps. Duodenal polyps that increase in size or number or show signs of becoming cancerous may require treatment. This treatment may include evaluation by computed tomography or ultrasonography. If necessary, the polyps may be removed by laser or other procedures.

For at-risk relatives of affected individuals, regular screening should begin between the ages of 10 and 12 years. This screening can be accomplished by protein truncation testing. If the test result is a true negative (i.e., negative result in a person whose affected relative had a positive result), further screening is debatable. This test result should theoretically eliminate the risk of FAP but, in very few cases, laboratory errors or other circumstances may lead to an inaccurate test result. Thus, some experts suggest that flexible sigmoidoscopy should be performed at ages 18, 25, and 35 years in these individuals, with standard screening thereafter.

After colectomy, continued surveillance of patients with FAP is advised. Ileoscopy is recommended every three to five years. This procedure examines the ileum, or lowest third of the small intestine, and serves to rule out polyps, which may become cancerous with time. Surgical removal of desmoid tumors is invasive but often necessary to prevent reoccurrence. Various nonoperative treatments have been attempted, such as medication and radiation, none of which have yielded consistent results. Additionally, the examination of any remaining rectal tissue by proctoscopy is necessary every six months to assess for signs of rectal cancer.

As with any abdominal surgeries in people affected with FAP, there is a risk of developing desmoid tumors after the colectomy. If desmoids are suspected, computed tomography is the recommended imaging study. MRI may also be used in certain cases.

Surveillance of the upper GI tract, even after total proctocoloectomy, is appropriate due to the incidence of tumors in this area previously discussed.