Differential Diagnosis
- Single most likely diagnosis
- Diverticulitis: The patient's symptoms of dull pain in the left lower quadrant (LLQ) radiating to the left lower back, occasional bloating, and changes in stool color are consistent with diverticulitis, especially given the absence of urinary symptoms and negative urinalysis. The presence of ketones may indicate some degree of dehydration or metabolic response to inflammation.
- Other Likely diagnoses
- Irritable Bowel Syndrome (IBS): Although the pain pattern and radiation to the back could fit, the recent change in stool appearance and the presence of ketones might suggest an inflammatory or infectious component not typical of IBS.
- Constipation: Could explain the bloating and changes in stool, but the pain pattern and radiation to the back, along with the systemic symptoms like ketones, make this less likely as a standalone diagnosis.
- Ovarian Cyst or Torsion: The left-sided pain and radiation to the back, along with the sensation of swelling in the left armpit (which could be referred pain), might suggest a gynecological cause, especially in a female patient.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Ectopic Pregnancy: Although less likely given the absence of specific symptoms like vaginal bleeding, this is a critical diagnosis to consider in any female patient of childbearing age presenting with abdominal pain.
- Appendicitis: While the pain is on the left side, which is atypical for appendicitis, the condition can occasionally present with pain in unusual locations, especially if the appendix is retrocecal.
- Intestinal Obstruction: The bloating and changes in stool could suggest an obstruction, which is a medical emergency.
- Kidney Stone or Pyelonephritis: Despite the negative urinalysis, these conditions can sometimes present with atypical symptoms, and the presence of ketones could indicate a systemic response to infection.
- Rare diagnoses
- Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease or ulcerative colitis could present with similar symptoms but are less common and typically have a more chronic course.
- Splenic Infarct or Rupture: Could explain the left-sided pain and referred pain to the left shoulder (via the left armpit), but these conditions are rare and usually associated with specific risk factors like trauma or sickle cell disease.
- Pancreatitis: Although the pain is not typically in the LLQ, pancreatitis can cause a wide range of abdominal pain patterns and should be considered, especially with systemic symptoms like ketones.