Differential Diagnosis
- Single most likely diagnosis
- Inflammatory Bowel Disease (IBD), specifically Ulcerative Colitis (UC): The patient's symptoms of recurrent episodes of abdominal cramping, diarrhea with bright red blood, and a sensation of incomplete evacuation are classic for UC. The absence of a family history does not rule out IBD, as many cases are sporadic. The improvement and resolution of symptoms between episodes also fit the pattern of IBD.
- Other Likely diagnoses
- Irritable Bowel Syndrome (IBS) with a component of rectal bleeding: While IBS typically does not cause bleeding, some patients may experience rectal bleeding due to hemorrhoids or anal fissures, which could be exacerbated by the bowel habits described. However, the presence of bright red blood and the pattern of symptoms suggest an inflammatory cause.
- Infectious colitis: Given the recurrent nature of the symptoms, infectious causes might be less likely, but certain infections (e.g., Clostridioides difficile) can cause recurrent episodes of diarrhea and abdominal pain.
- Do Not Miss diagnoses
- Colon cancer: Although rare in young individuals, colon cancer can present with similar symptoms, including rectal bleeding and changes in bowel habits. The recent weight fluctuation could also be a red flag for malignancy.
- Intestinal ischemia: This condition can cause severe abdominal pain and bloody diarrhea, especially if the ischemia involves the colon. It is less likely given the patient's age and the recurrent, self-resolving nature of the symptoms, but it should not be missed due to its high morbidity and mortality.
- Invasive intestinal infections (e.g., amoebiasis, particularly in immunocompromised or travelers): These can cause dysentery (bloody diarrhea) and are important to consider, especially if the patient has risk factors for exposure.
- Rare diagnoses
- Eosinophilic colitis: A rare condition characterized by eosinophilic infiltration of the colon, which can cause abdominal pain, diarrhea, and sometimes rectal bleeding.
- Allergic colitis: More commonly seen in infants but can occur in adults, presenting with similar gastrointestinal symptoms.
- Microscopic colitis: Can cause chronic watery diarrhea but is less likely to cause bloody stools. However, it's a consideration in patients with chronic gastrointestinal symptoms without an obvious cause.