Differential Diagnosis

The patient's presentation of localized left lower quadrant (LLQ) and left suprapubic pain, worsened at night and relieved during the day, along with episodes of diarrhea and mildly elevated transaminases, suggests several potential diagnoses. Here is a categorized differential diagnosis:

• Single Most Likely Diagnosis

  • Diverticulitis: Given the patient's age and the nature of the pain (localized LLQ pain worse at night), diverticulitis is a strong consideration. The absence of significant findings on CT abdomen/pelvis with contrast does not entirely rule out early or mild diverticulitis, especially if the study was not specifically focused on the colon or if the disease is in its early stages.

• Other Likely Diagnoses

  • Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease or ulcerative colitis could present with abdominal pain, diarrhea, and elevated liver enzymes. The normal urinalysis and absence of nausea/vomiting do not rule out IBD.
  • Irritable Bowel Syndrome (IBS): Although IBS is more chronic, the patient's symptoms of abdominal pain and alteration in bowel habits (diarrhea) could fit this diagnosis. However, the acute onset and nocturnal worsening might be less typical.
  • Gastroenteritis: Despite the lack of nausea and vomiting, gastroenteritis could still be a consideration, especially with the episodes of diarrhea. The mild elevation in transaminases could be seen in some viral gastroenteritides.

• Do Not Miss Diagnoses

  • Appendicitis: Although the pain is in the LLQ, appendicitis can present atypically, especially if the appendix is retrocecal. The absence of significant findings on CT does not entirely rule out appendicitis, particularly if the appendix was not well visualized.
  • Ectopic Pregnancy: Although less likely in a male patient, it's essential to consider in any patient of reproductive age presenting with abdominal pain. However, given the patient is male, this is extremely unlikely.
  • Intussusception: A rare condition in adults, but it can cause intermittent abdominal pain and alterations in bowel habits. It's a diagnosis that would be critical to identify due to the potential need for urgent intervention.
  • Ovarian Torsion: Again, unlikely in a male patient, but any condition causing severe, acute abdominal pain warrants consideration of torsion of intra-abdominal organs.

• Rare Diagnoses

  • Meckel's Diverticulitis: A rare condition that could present with abdominal pain and might be missed on initial imaging if not specifically looked for.
  • Mesenteric Lymphadenitis: Could mimic appendicitis or other causes of abdominal pain and might not be evident on CT scan unless lymph nodes are specifically evaluated.
  • Chronic Intestinal Pseudo-obstruction: Presents with abdominal pain and alterations in bowel habits but is rare and typically associated with more significant gastrointestinal dysmotility symptoms.