Right lower abdominal pain and diarrhea: what diagnoses are usually considered first?

Right lower abdominal pain and diarrhea often point to inflammation or infection of the terminal ileum or cecum. Many conditions can cause these symptoms. Below is a concise overview of the most common diagnoses to consider first, how they present, and what to expect next.

What to consider first
• Acute appendicitis
• Infectious ileocolitis (bacteria, parasites, viruses)
• Crohn’s disease (ileitis)
• Mesenteric adenitis
• Meckel’s diverticulitis
• Ileocecal tuberculosis
• NSAID-induced enteropathy
• Irritable bowel syndrome (IBS)
• Less common: ischemia, tumors

1. Acute appendicitis
   • Presentation: periumbilical pain migrating to right lower quadrant (RLQ), often with nausea, low-grade fever, sometimes diarrhea
   • Why diarrhea? Inflammation irritates adjacent bowel loops or an appendiceal abscess may leak fluid
   • Key signs: McBurney’s point tenderness, rebound pain, elevated white blood cell count
   • Next steps: ultrasound or CT scan; surgical consult if imaging and exam suggest appendicitis

2. Infectious ileocolitis / ileitis
   Bacterial pathogens invade or inflame the distal small bowel and cecum, causing crampy RLQ pain and diarrhea.

• Yersinia enterocolitica
– Reservoir in pigs; often undercooked pork or unpasteurized milk
– Fever, bloody or mucoid diarrhea, RLQ pain mimicking appendicitis (pseudoappendicitis)
– Diagnosis: stool culture, serology
– Treatment: supportive; antibiotics (e.g., fluoroquinolones) in severe cases (Bottone EJ, 1997)
• Salmonella, Campylobacter, Shigella
– Watery to bloody diarrhea, systemic symptoms
– Often self-limiting; antibiotics reserved for high-risk patients
• Clostridioides difficile
– Recent antibiotic use; profuse watery diarrhea, sometimes RLQ cramping
– Diagnose with stool toxin assay; treat with oral vancomycin or fidaxomicin
• Parasitic (Giardia, Entamoeba histolytica)
– More chronic diarrhea, possible malabsorption
– Confirm with stool ova & parasite exam

3. Crohn’s disease (terminal ileitis)
   • Presentation: chronic or relapsing RLQ pain, diarrhea (sometimes bloody), weight loss, fatigue
   • Extraintestinal signs: mouth sores, arthritis, skin rashes
   • Diagnosis:
   – Laboratory: elevated CRP/ESR, anemia
   – Imaging: CT/MR enterography showing ileal wall thickening, strictures
   – Endoscopy: ileocolonoscopy with biopsy (granulomas)
   • Why consider it early? Up to 30% of ileitis cases are Crohn’s; delay in diagnosis can lead to complications (Rieder & Fiocchi, 2014)

4. Mesenteric adenitis
   • Often in children/young adults after a viral illness
   • Tender RLQ lymph nodes cause pain; diarrhea may be mild or absent
   • Ultrasound: enlarged mesenteric lymph nodes, normal appendix
   • Management: supportive care; resolves in days

5. Meckel’s diverticulitis
   • True diverticulum in distal ileum; can inflame or bleed
   • Symptoms: RLQ pain, painless bleeding or diarrhea if ectopic gastric mucosa
   • Diagnosis: technetium-99m pertechnetate scan (“Meckel’s scan”)
   • Treatment: surgical resection if symptomatic

6. Ileocecal tuberculosis
   • Risk factors: immunosuppression, endemic areas
   • Symptoms: chronic RLQ pain, weight loss, fever, diarrhea
   • Findings: ileocecal thickening on CT, caseating granulomas on biopsy
   • Treatment: standard anti-TB regimen

7. NSAID-induced enteropathy
   • Chronic NSAID use can cause right-sided small bowel inflammation
   • Presentation: crampy pain, diarrhea, sometimes bleeding
   • Diagnosis: capsule endoscopy, enteroscopy
   • Management: stop NSAIDs, start protective agents (e.g., misoprostol)

8. Irritable bowel syndrome (IBS)
   • Recurrent abdominal pain with altered bowel habits; no structural disease
   • RLQ discomfort may occur with diarrhea-predominant IBS
   • Diagnosis: clinical (Rome IV criteria), exclude alarm features
   • Management: diet (low-FODMAP), stress management, antispasmodics

Less common causes
• Mesenteric ischemia (arterial or venous): sudden severe pain, often in older patients with vascular disease
• Neoplasm (ileocecal tumors, lymphoma): insidious onset, weight loss, possible obstruction
• Radiation enteritis: history of pelvic or abdominal radiotherapy

Key steps in evaluation

1. Detailed history
   – Onset, duration, character of pain
   – Stool pattern (frequency, blood, mucus)
   – Associated symptoms (fever, weight loss, nausea)
   – Medication use (NSAIDs, antibiotics)
   – Travel, dietary exposures, sick contacts
2. Physical exam
   – Vital signs (fever, tachycardia)
   – Abdominal exam (localized tenderness, peritoneal signs)
   – Rectal exam (masses, blood)
3. Laboratory tests
   – CBC, CRP/ESR for inflammation
   – Electrolytes if diarrhea is severe
   – Stool studies: culture, C. difficile toxin, ova & parasites
4. Imaging
   – Ultrasound: first-line in children, pregnant patients
   – CT scan with contrast: excellent for appendicitis, ileitis, abscesses
   – MR enterography: detailed small-bowel evaluation in suspected Crohn’s
5. Endoscopy
   – Colonoscopy with intubation of terminal ileum for suspected IBD or TB
   – Capsule endoscopy for small-bowel mucosal disease

When to seek immediate care
• Severe, constant abdominal pain or worsening pain
• High fever (> 101°F/38.3°C)
• Persistent vomiting or inability to keep fluids down
• Signs of dehydration (dizziness, low urine output)
• Blood in stool or black/tarry stool
• Rapid heart rate or low blood pressure

Next steps & resources
If you’re wondering what might be causing your right lower abdominal pain and diarrhea, you might consider doing a free, online symptom check. This can help you gather information before talking with a healthcare provider.

Remember, this overview does not replace a medical evaluation. Always speak to a doctor about any symptoms that could be life threatening or serious. A prompt assessment—including physical exam, labs, and imaging—ensures the correct diagnosis and timely treatment.