CASE
An 18-year-old Hispanic female presented to the emergency department with a 4-day history of nausea, vomiting, diarrhea with persistent hematochezia, and diffuse abdominal pain. The patient also reported decreased appetite beginning 2 days before the onset of her current symptoms. She described the abdominal pain as waxing and waning, with episodes of greatest intensity lasting from 10 to 30 minutes. She denied any previous history of abdominal illness. Results of GU and gynecologic assessments were negative.
Evaluation On the medical and family history questionnaire she completed at check-in, the patient reported no significant personal or family history of GI disorders. When asked specifically about GI problems during history-taking, she noted that several family members on her mother's side had large scars on their abdomens. She was unaware of the reasons for the scars but believed that her relatives had undergone surgery in their home country of Mexico. She further stated that her family did not discuss such matters.
Vital signs were within normal limits: BP was 121/75 mm Hg; heart rate, 74 beats per minute; and respiration rate, 18 breaths per minute. The patient was afebrile. Physical examination revealed hypoactive bowel sounds in all four quadrants and diffuse tenderness to palpation without guarding or rebound. There was no evidence of organomegaly, pulsations, bruits, or flank pain. Findings on ophthalmologic and gynecologic examinations were unremarkable; there was no evidence of lipomas, osteomas, dental abnormalities, or thyroid nodules.
Laboratory studies A CBC with differential revealed low hemoglobin, low hematocrit, and normal RBC indices, findings indicative of a normocytic, normochromic anemia (Table 1). A comprehensive metabolic panel showed electrolyte levels to be within normal range, as were the results of urinalysis and tests for amylase, lipase, and alphafetoprotein. Prothrombin time and partial thromboplastin time were unremarkable. A carcinoembryonic antigen (CEA) level was elevated, and results of a fecal occult blood test were positive for gross blood in the stool. The elevated CEA level along with occult blood in the stool raised the suspicion for colon cancer. The patient's blood was typed, and a crossmatch was ordered. She was then admitted to the hospital's surgical service for further evaluation.
Colonoscopy and biopsy At colonoscopy the following morning, the patient had more than 100 polyps in her colon. No hemorrhoids or rectal masses were visible. Tissue samples from the polyps were sent to pathology for further analysis. The biopsy results were consistent with tubular adenoma and adenocarcinoma, confirming the diagnosis of familial adenomatous polyposis (FAP). The patient was advised to undergo total proctocolectomy with ileal pouch-anal anastamosis (IPAA). After the risks, benefits, and complications of the procedure were explained, the patient consented to the surgery. She was given an oral solution to prepare her bowel and scheduled for surgery the following day.
DISCUSSION
FAP is an autosomal dominant syndrome that results from a germline mutation of the adenomatous polyposis coli (APC) tumor suppressor gene located on chromosome 5. The mutation often results in the truncation of a protein responsible for the control of cell adhesion, signaling, and apoptosis.1 More than 300 pathogenic mutations of the APC gene have been recorded in the Human Genome Mutation Database.1
Worldwide, FAP affects up to 1 in every 22,000 live births, with an equal distribution between males and females.2 The mean age for the development of adenomatous polyps is 15 years; as many as 100 adenomas may develop in patients with FAP in their second decade.1 Close to 100% of patients with FAP will develop polyps by the time they are 35 years old; without prophylactic polypectomy, colorectal cancer is a near certainty by age 50.3 FAP accounts for approximately 1% of all colon cancers in the United States.4
Diagnosis of FAP is based on endoscopic findings of more than 100 colonic polyps and a family history.4 However, up to 30% of patients with FAP present without any family history of the disorder.4 In these instances, genetic screening is helpful to confirm the diagnosis.4 Genetic screening is also recommended in children 10 years or older who have a family history of FAP.4 The protein truncation assay is a useful tool, but its sensitivity for FAP is only 80%.4 Another tool for genetic screening of FAP is the fecal DNA test, which uses polymerase chain reaction of DNA that is recovered from stool samples to detect mutations in the APC gene.5
Extraintestinal manifestations of FAP are variable and depend on the site of APC gene mutations.6 Gardner's syndrome is the presence of FAP with lipomas, desmoid tumors, osteomas, congenital hypertrophy of the retinal pigment, and dental abnormalities.6 Turcot's syndrome is the presence of FAP with mali gnancies of the CNS, papillary thyroid carcinoma, hepatoblastomas, or medulloblastoma.6