Condition
Change in bowel habits
Other characteristics
Colorectal cancer
Diarrhea, constipation, iron deficiency anemia (more so with right sided)
Anemia, fatigue, weight loss, decreased stool caliber
Irritable bowel syndrome (IBS)
Diarrhea alternating with constipation, +/− mucus, no blood
Symptom-based diagnosis, chronic abdominal pain relieved by BM, bloating, tenesmus, depression/anxiety common
IBD (ulcerative colitis or Crohn’s disease)
Diarrhea +/− blood, mucus
Abdominal pain, severe cramps, weight loss, anemia (see section below)
Celiac disease
Pale, loose and greasy stool (steatorrhea), diarrhea
Weight loss, failure to thrive (in children), malabsorption, anemia, dermatitis herpetiformis (autoimmune maculopapular rash)
Intestinal pseudo-obstruction
Constipation
Bowel distention in the absence of anatomic lesions, abdominal distention, succussion splash, nausea, vomiting
Thyroid disease
Diarrhea (hyperthyroid) or constipation (hypothyroid)
Anxiety, tremor, palpitations, heal intolerance with hyperthyroidism; fatigue, cold intolerance with hypothyroidism
Drugs (laxatives, antidiarrheal)
Diarrhea or constipation
Medication-induced change in bowel habits, melanosis coli, weight loss, psychosocial comorbidities
Infectious
Diarrhea
Viral, bacterial or parasitic infection
What Is the Most Likely Diagnosis?
Given the patient’s bowel symptoms, anemia, weight loss, and age, the most likely diagnosis is colon cancer until proven otherwise. His predominant symptoms are those of a slowly obstructing lesion as evidenced by a change in bowel habits with pencil-thin stools, which is most suggestive of a left-sided lesion.
Screening
What Screening Is Recommended for Colorectal Cancer?
The US Preventive Services Task Force (USPSTF) recommends screening in all adults of average risk, beginning at age 50 until age 75. The decision to screen individuals between 75 and 85 is made on an individual basis, whereas screening is not recommended for individuals over age 85. In patients with IBD, the screening recommendations vary.
What Screening Is Recommended for Colorectal Cancer in Patients with a First-Degree Family Member with Colorectal Cancer?
These patients should begin screening at age 40 or 10 years prior to the onset of colorectal cancer in the first-degree relative, whichever comes first. They should continue screening every 5 years after.
What Are the Differences Between the Various Screening Modalities?
The decision to use a particular screening tool needs to be made by the patient after discussing the benefits, risks, and financial considerations imposed on the patient. Table 21.1 goes over the key differences.
Table 21.1
Screening for colorectal cancer
Screening | USPST Fa | Interval | Features |
|---|---|---|---|
Colonoscopy | Yes | Every 10 years | Visualizes the entire rectum and colon, can detect lesions less than 0.5 cm, able to remove polyps and attain biopsies, used as a follow-up test if other tests are equivocal, sedation required, 0.2 % perforation risk |
Flexible sigmoidoscopy | Yes | Every 5 years + FOBT every 3 years | Limited to only the lower third of the colon, able to remove polyps and attain biopsies, sedation required; if + FOBT, must undergo colonoscopy |
Fecal occult blood test (FOBT) | Yes | Annually | Of two types: traditional hemoccult chemical test (requires dietary modifications 3 days prior) and newer immunochemical test (greater sensitivity, lower specificity), can be done at home, positive test requires follow-up with colonoscopy |
Barium enema with sigmoidoscopy | No | Every 5 years | Sigmoidoscopy is a mandatory adjunct to barium enema as the rectum is not well visualized, detects only 50 % of polyps larger than 1 cm, sedation not required, detection of mucosal inflammation is limited, useful if colonoscopy is incomplete owing to anatomic or pathologic barriers |
CT colonography | No | Every 5 years | As likely as colonoscopy to detect lesions 10 mm or larger but may be less sensitive for smaller adenomas, requires bowel prep, does not require sedation, may identify incidental findings (i.e., extracolonic neoplasms or AAA), and does not allow for biopsy or polypectomy |
Capsule endoscopy | No | Every 5 years | Low sensitivity/specificity, unable to attain biopsies, less invasive but requires more aggressive bowel prep, not available in the USA for screening |
Watch Out
Diets rich in red meat can result in a false-positive fecal occult blood test (FOBT) test.
History and Physical
What Is the Significance of the Patient’s Unintended Weight Loss?
Unexplained weight loss is a cause for concern because it may suggest malignancy. In patients with colorectal carcinoma, it may signify disseminated disease. Although the pathogenesis of cancer-related cachexia is not fully understood, TNF-alpha seems to play a central role and has direct catabolic effects on skeletal muscle. Other causes of unexplained weight loss include depression, celiac disease, Addison’s disease, chronic obstructive pulmonary disease, IBD, HIV, peptic ulcer disease, tuberculosis, and hyperthyroidism.
What Are the Risk Factors for Colon Cancer?
The risk factors for colon cancer include older age (majority are over 50), African American race, IBD, family history, low-fiber/high-fat diet, sedentary lifestyle, obesity, smoking, alcohol, type 2 diabetes, and radiation therapy to the abdomen.
Where Does Colon Cancer Rank in Terms of the Most Common Cancers in the Usa? In Terms of the Highest Overall Mortality?
Incidence (in order of frequency) | Mortality (highest first) | |
|---|---|---|
Men | Prostate, lung, and colon | Lung, prostate, and colon |
Women | Breast, lung, and colon | Lung, breast, and colon |
Are Right- or Left-Sided Colon Cancers More Common and How Do the Presentations Differ?
The majority of colon cancers are left sided and occur near the rectosigmoid junction. Left-sided colon cancers are more likely to cause a change in bowel habits and symptoms of obstruction. When stool reaches the sigmoid, it is often hard and devoid of excess fluid. The caliber of the lumen is also narrower on the left side, and with a circumferential tumor causing partial obstruction, patients report pencil-thin stools, often tinged with blood. Bowel habits can alternate between constipation and diarrhea. Patients report distention with lower abdominal colicky pain. Since the lesions are closer to the anal orifice, bright red blood per rectum (hematochezia) may be reported. A smaller number of colon cancers are right sided, and the most common finding is an insidious onset of iron deficiency anemia secondary to chronic GI blood loss. Rarely, if the tumor is rapidly growing, patients can experience severe pain, and a right lower quadrant mass may be appreciated on exam.
Watch Out
Melena is more common in right-sided colon cancers.
Why Is the Rectal Examination Important in Suspected Colorectal Cancer?
The digital rectal exam (DRE) is often overlooked by the novice, yet it is of critical importance in the evaluation of a patient with possible colorectal cancer. A DRE by itself is not a good test for detecting colon cancer because its reach is limited. However, the value of the DRE lies in its ability to detect low rectal cancers because it allows the examiner to feel a mass, which is suggestive of malignancy. In addition, distance from the anal verge, mobility, and anatomic relation to other pelvic structures can be assessed. A fixed mass is more likely to be locally advanced, and relation to the prostate, vagina, and sacrum is important for surgical planning.
Pathophysiology
What Is a Polyp and How Are They Generally Classified?
A polyp is a mass that protrudes into the lumen of the GI tract and can either be pedunculated (with a stalk) or sessile (flat). Nonneoplastic polyps can arise from abnormal mucosal maturation, inflammation, or colonic architecture. However, polyps arising from epithelial proliferation and dysplasia are true neoplasms and may have malignant potential. They are collectively known as adenomatous polyps or adenomas.
Watch Out
Juvenile polyposis syndrome can result in a large number of hamartomatous polyps in the stomach and colon occurring in children. Multiple hamartomatous polyps alongside with mucocutaneous hyperpigmentation spots on the lips and genitalia are concerning for Peutz-Jeghers syndrome.
Describe the Nonneoplastic Polyps
Type | Features |
|---|---|
Hyperplastic | Small (<5 mm in diameter) and smooth; the most common type; isolated polyps are typically benign it is now recognized that there are hyperplastic polyposis syndromes in which there may be a risk of malignancy |
Juvenile (hamartomatous) | Rounded, smooth, and sometimes have a stalk (<2 cm); occur most commonly in children (<5 year old); usually present as a solitary rectal polyp that prolapses and the term “juvenile” refers to the way these polyps look under the microscope |
How Do Colon Cancers Develop?
The majority of colon cancers arise from the adenoma-carcinoma sequence (Fig. 21.1). This is also known as the chromosome instability pathway since there is a stepwise accumulation of mutations leading to carcinoma. The sequence begins with a loss of the APC tumor suppressor gene resulting in decreased intercellular adhesion and increased proliferation. A subsequent KRAS mutation achieves unregulated intracellular signaling and transduction which allows for the formation of an adenoma. Adenomatous polyps are considered premalignant and it is estimated that 20 % will go on to become malignant. The malignant potential of an adenomatous polyp is related to the age of the patient, the size of the polyp, and the villous component. Finally, loss of the p53 tumor suppressor gene will increase tumorigenesis in an adenoma and result in carcinoma. In a smaller number of colon cancers, microsatellite instability plays a bigger role in which impaired DNA mismatch repair enzymes are unable to ensure the fidelity of a copied DNA strand, increasing the risk for developing cancer.
