Pathophysiology
P-II-1. Gastrointestinal disease, Case 1
消化管疾患 症例1
Female patient, 25 years old, has had watery diarrhea for 3 weeks, with intermittent fresh red blood in her stools. Four days ago she developed fever; since then she has had more frequent diarrhea (seven to eight times a day), which now consistently contains fresh red blood and mucus. She has vomited a few times; her vomit has not been bloody or like coffee grounds. She has constant, cramping pain around her navel. No history of illness, no medication.
On examination: female patient in a state of distress. Dry, scaly tongue, skin turgor decreased, symmetric thorax, normal breathing sounds and bilateral chest excursion, heart rhythmic, clear cardiac sounds, no murmur can be heard, HR: 96/min, RR: 100/75 mmHg, abdomen soft, palpable, no abnormal resistance, no defense, but marked periumbilical tenderness, left side of abdomen and lower abdomen. Well palpable peripheral vessels, no vascular murmurs can be heard.
Laboratory abnormalities to highlight: Hgb: 118 g/l, Htk: 33%, RBC: 4 T/l, WBC: 11.9 G/l, BUN: 8.5 mmol/l, K: 3.3 mmol/l, CRP: 117.4 mg/l.
Fecal culture: no pathogenic bacteria have been cultured.
Abdominal ultrasound: the descending colon and the wall of the sigmoid colon are edematous, inflamed, no free abdominal fluid.
Colonoscopy: moderate inflammation and a few small ulcers can be seen in the rectum, sigmoid and descending colon.
Key Quotes & What They Tell Us
| Quote / Value | Interpretation |
|---|---|
| “watery diarrhea for 3 weeks … fresh red blood … and mucus”, 7–8×/day | Chronic bloody, mucoid diarrhoea → inflammatory (not just secretory) colitis |
| “Fecal culture: no pathogenic bacteria” | Excludes an infectious cause → favours inflammatory bowel disease |
| Colonoscopy: inflammation/ulcers in “rectum, sigmoid and descending colon” | Continuous disease extending proximally from the rectum → typical of ulcerative colitis |
| “Dry, scaly tongue, skin turgor decreased”; K⁺ 3.3 (low); BUN 8.5 (high) | Dehydration and potassium loss from prolonged diarrhoea |
| CRP 117 mg/L; WBC 11.9 G/L; fever | Marked systemic inflammation / active flare |
| Hgb 118 g/L, Htk 33% (mild anaemia) | Blood loss / anaemia of chronic inflammation |
Key Points
- Diagnosis: Ulcerative colitis (a form of inflammatory bowel disease), presenting as an acute flare.
- Distinguishing features: Continuous inflammation starting in the rectum and extending proximally; bloody, mucoid diarrhoea; mucosal ulcers on colonoscopy.
- Exclusion of infection: Negative stool culture supports IBD over infectious colitis.
- Pathophysiology: Immune-mediated mucosal/submucosal inflammation of the colon → ulceration, bleeding, and impaired water/electrolyte absorption.
- Complications shown: Dehydration, hypokalaemia, anaemia, and a strong systemic inflammatory response.
一問一答
▶What colonoscopy pattern is typical of ulcerative colitis?
Continuous inflammation and ulceration starting at the rectum and extending proximally (here rectum, sigmoid, descending colon).
▶What is the diagnosis in a young woman with 3 weeks of bloody, mucoid diarrhoea and continuous colonic ulcers from the rectum?
Ulcerative colitis (a form of inflammatory bowel disease) in an acute flare.
▶Why does a negative stool culture support inflammatory bowel disease here?
It excludes an infectious cause of the colitis, favouring an immune-mediated IBD.
▶What is the pathophysiology of ulcerative colitis?
Immune-mediated inflammation of the colonic mucosa/submucosa causing ulceration, bleeding, and impaired water/electrolyte absorption.
▶Why does the patient have a dry tongue, decreased skin turgor, and high BUN?
Dehydration from prolonged frequent diarrhoea, causing pre-renal volume depletion.
▶Why is potassium low (3.3 mmol/L) in this patient?
Prolonged diarrhoea causes significant gastrointestinal potassium loss.
▶Why is this patient mildly anaemic (Hgb 118 g/L)?
Ongoing intestinal blood loss plus anaemia of chronic inflammation.
▶What does a CRP of 117 mg/L with leukocytosis and fever indicate?
A marked systemic inflammatory response consistent with an active colitis flare.
▶Why does ulcerative colitis cause bloody, mucoid stools?
Mucosal ulceration and inflammation lead to bleeding and excess mucus secretion into the lumen.
▶How does ulcerative colitis differ from Crohn's disease in distribution?
UC is continuous and limited to the colon starting at the rectum; Crohn's is patchy ('skip lesions') and can affect any part of the GI tract.
▶What does the ultrasound finding of an edematous, inflamed sigmoid/descending colon wall indicate?
Active colonic wall inflammation consistent with the colitis.
▶Why is the absence of coffee-ground or bloody vomit relevant?
It argues against an upper GI bleed, localizing the bleeding to the lower GI tract (colon).
▶Why does prolonged colonic inflammation impair water and electrolyte balance?
Inflamed mucosa cannot adequately absorb water and electrolytes, causing watery diarrhoea and depletion.
▶Why does the patient have periumbilical and left-sided abdominal tenderness?
Inflammation of the descending and sigmoid colon (left-sided) produces tenderness in those regions.
▶What is a dangerous acute complication of severe ulcerative colitis?
Toxic megacolon (with risk of perforation).
▶Why is tachycardia (HR 96) with low-normal BP concerning in this patient?
It reflects compensatory response to dehydration/volume loss from severe diarrhoea.
▶What long-term risk is associated with chronic ulcerative colitis?
Increased risk of colorectal cancer with long-standing extensive disease.
▶What are the initial supportive treatment priorities in this acute flare?
Rehydration and electrolyte (especially potassium) replacement alongside anti-inflammatory therapy.
▶Why is colonoscopy with biopsy important in diagnosing ulcerative colitis?
It defines the extent and continuous pattern of inflammation and confirms the diagnosis histologically.
▶Why does ulcerative colitis characteristically begin in the rectum?
UC starts at the rectum and spreads continuously and proximally, so the rectum is almost always involved.