What is the cause of a 51-year-old female's acute right abdominal pain that started 3 weeks ago, with a history of normal bowel movements (BM) every 3 days, but recently passing stool in the form of balls, despite increased fiber intake, and experiencing intermittent pain in the rib and lower abdominal areas?

Differential Diagnosis for Acute Right Abdominal Pain

Single Most Likely Diagnosis

• Constipation with possible fecal impaction: Given the patient's bowel history of having a bowel movement every 3 days, which is normal for her, and the fact that her stools come out as balls, it suggests constipation. The abdominal pain could be related to the constipation, especially if she has a fecal impaction. The pain can radiate to different areas, including the rib and lower abdominal areas.

Other Likely Diagnoses

• Irritable Bowel Syndrome (IBS): The patient's symptoms of abdominal pain and changes in bowel habits could be consistent with IBS, especially if the pain is crampy and relieved by bowel movements.
• Gallbladder disease: The patient's pain location in the right abdomen and sometimes radiating to the rib area could suggest gallbladder disease, such as cholecystitis or gallstones.
• Diverticulitis: Although less common on the right side, diverticulitis could cause abdominal pain, especially if the patient has a history of diverticula.

Do Not Miss Diagnoses

• Appendicitis: Although the patient's pain has been present for 3 weeks, appendicitis can present atypically, especially in older adults. It's crucial to consider this diagnosis due to its potential for serious complications if missed.
• Ovarian torsion or ovarian cyst: These conditions can cause severe abdominal pain and are emergencies that require prompt attention.
• Intestinal obstruction: This is a life-threatening condition that requires immediate medical attention. Although the patient's bowel history and symptoms do not strongly suggest this, it's essential to consider it in the differential diagnosis.

Rare Diagnoses

• Inflammatory bowel disease (Crohn's disease or ulcerative colitis): These conditions can cause chronic abdominal pain, changes in bowel habits, and other symptoms. However, they are less likely given the patient's age and presentation.
• Carcinoid syndrome: This rare condition can cause abdominal pain, changes in bowel habits, and other symptoms, but it is much less likely and would require further evaluation to diagnose.
• Abdominal wall hernia: Although possible, this diagnosis is less likely given the patient's symptoms and presentation.