Inflammatory bowel disease: Pathology review
AssessmentsInflammatory bowel disease: Pathology review
USMLE® Step 1 style questions USMLE
A 32-year-old man comes to the office with complaints of pain in the hip joint and stiffness in the lower back for the past month. The symptoms are worse in the morning and improve with activity and exercise. Review of systems reveals intermittent abdominal pain and frequent episodes of small-volume bloody diarrhea for the last 3 months. He tried over-the-counter analgesics, which helped the joint pain but made the diarrhea worse. He does not have any pain with urination and has not traveled recently. The remainder of his history is noncontributory. Vitals are within normal limits. BMI is 22 kg/m2. Physical examination shows mild tenderness in the hip joints and limited spinal flexion. Laboratory analysis is shown below:
|Complete blood count|
Plain radiographs show signs of sacroiliac joint inflammation. Which of the following is the most likely cause of this patient’s joint pain?
Content Reviewers:Yifan Xiao, MD
Contributors:Tina Collins, Kaylee Neff, Antonella Melani, MD
Alex is a 21 year old college student who has a 2 month history of frequent episodes of abdominal pain and bloody diarrhea. Chris is also a 21 year old college student with painful ulcers in the mouth, intermittent abdominal pain, and non-bloody diarrhea that’s been going on for years. In addition, Chris has a history of recurrent kidney stones.
After careful examination, colonoscopy is ordered in both cases. In Alex’s case, there’s circumferential inflammation that’s continuous throughout an entire section of the rectum and colon. On the other hand, in Chris’ case, there are linear patches of damaged colon with normal mucosa in between, and the rectum is not involved.
Alex and Chris both have inflammatory bowel disease or IBD, which is characterized by chronic gastrointestinal tract inflammation due to autoimmune reactions, as well as systemic symptoms like fatigue, fever and unintentional weight loss. IBD typically has its onset before the age of 30. The exact cause is unknown, but there’s definitely a genetic component because it runs in families. Now, there are two types of IBD - Crohn’s disease and ulcerative colitis.
Okay, now let’s look at each specific disease, starting with Crohn’s disease, which is mostly caused by an abnormal Th1 cellular response, and a known risk factor is smoking. In Crohn’s disease, the inflammation can pop up anywhere in the GI tract, from the mouth to the anus, but the rectum is often spared. It tends to be most severe at the terminal ileum.
Gastrointestinal symptoms include crampy abdominal pain, watery diarrhea that may or may not be bloody, and sometimes malabsorption symptoms like malnutrition, steatorrhea, or B12 deficiency. A very frequent finding to keep in mind are aphthous ulcers in the mouth. Some individuals may also present esophageal involvement, with odynophagia and dysphagia.
Extraintestinal symptoms include arthritis, uveitis and episcleritis, and skin lesions like pyoderma gangrenosum and erythema nodosum. In addition, a high yield fact is that Crohn’s disease leads to a higher risk of kidney stones and gallstones. That’s because damage to the terminal ileum decreases absorption of fats and bile salts in the intestine. The fats bind to calcium, which prevents the calcium from binding to oxalates. Free oxalates are absorbed in the intestine and eventually lead to calcium oxalate stones in the kidneys. On the other hand, the bile salts normally bind to cholesterol to make it water soluble. If there’s a decreased absorption of bile salts, cholesterol can collect and form stones in the gallbladder.
Over time, Crohn’s disease may lead to complications like strictures, which can cause bowel obstruction. Another complication are fistulas, which are communications between two epithelial organs, like from one part of the intestines to another, or from the intestines to another organ like the bladder or the skin surface.
Sometimes, a phlegmon can form, which is where there’s a localized area of inflammation in the intestinal wall that can get infected and become an abscess. Sometimes individuals get perianal abscesses, fissures, and fistulas. Finally, individuals with Crohn's disease may be at increased risk for colorectal cancer.
Okay, let’s switch gears to ulcerative colitis, which is mostly caused by an abnormal Th2 cellular response. Now, strangely enough, smoking has a protective effect in ulcerative colitis. The inflammation usually starts in the rectum and goes retrograde through the colon, but doesn’t extend to the rest of the GI tract.
Gastrointestinal symptoms include colicky abdominal pain, bloody diarrhea due to the inflammation that makes the GI mucosa frail, and tenesmus due to rectal involvement.
Extraintestinal symptoms can include iron deficiency anemia due to blood loss, as well as arthritis, uveitis and episcleritis, primary sclerosing cholangitis, and skin lesions like pyoderma gangrenosum and erythema nodosum.
Finally, complications of ulcerative colitis include severe gastrointestinal bleeding and fulminant colitis, which is continuous bleeding and over 10 stools per day. Another dangerous complication is toxic megacolon, which is where the nerves and muscles are damaged and the colon becomes atonic and dilated. In severe cases, it can lead to perforation with peritonitis, which causes fevers and severe abdominal pain. Finally, it’s important to know that ulcerative colitis increases the risk for colorectal cancer even more than Crohn’s disease.
All right, so for diagnosis of IBDs, an endoscopy or colonoscopy with biopsy is needed, and you need to know the findings for your exams! So Crohn’s disease lesions on endoscopy or colonoscopy look like linear patches of damaged tissue with normal GI mucosa in between, and these are called skip lesions. These damaged areas give the bowel a “cobblestone” appearance. In some individuals, the mesenteric fat may wrap around the bowel, causing it to thicken, and this is called the “creeping fat” sign.
- "Robbins Basic Pathology" Elsevier (2017)
- "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
- "First Aid for the USMLE Step 1 2018, 28th Edition" McGraw-Hill Education / Medical (2017)