Diverticulitis: This condition is a common cause of left lower quadrant abdominal pain, especially in older adults. It occurs when diverticula in the colon become inflamed, leading to pain, tenderness, and potentially more severe complications if not treated.

Constipation: Constipation can cause significant abdominal pain and discomfort, often localized to the left side due to the location of the descending colon.
Irritable Bowel Syndrome (IBS): IBS can present with abdominal pain, bloating, and changes in bowel habits. The pain is often crampy and can be localized to the left side.
Kidney Stone: While kidney stones can cause pain anywhere in the abdomen or back, stones in the lower pole of the kidney can sometimes cause left-sided abdominal pain.
Ovarian Cyst (in females): Ovarian cysts can cause intermittent or constant pain, usually on one side of the lower abdomen.

Ectopic Pregnancy (in females): Although less common, an ectopic pregnancy can present with severe, sudden-onset abdominal pain, often on one side, and is a medical emergency.
Appendicitis (if pain migrates or is accompanied by other symptoms): While appendicitis typically presents with right lower quadrant pain, it can occasionally present atypically, especially if the appendix is retrocecal or in an unusual position.
Intestinal Obstruction: This is a condition where there is a blockage in the intestines that can cause severe abdominal pain, vomiting, and constipation. It requires immediate medical attention.
Ruptured Abdominal Aortic Aneurysm: This is a life-threatening condition where the aorta ruptures, causing severe abdominal and back pain. It is more common in older adults with risk factors for vascular disease.

Splenic Infarction or Rupture: Conditions affecting the spleen can cause left upper quadrant pain and are more common in individuals with certain medical conditions or after trauma.
Pancreatitis: While pancreatitis often causes mid-abdominal pain, it can sometimes radiate to the left side, especially if the tail of the pancreas is involved.
Gastrointestinal Lymphoma or Other Cancers: These can cause chronic abdominal pain and are important to consider in the differential diagnosis, especially in individuals with risk factors or unexplained weight loss.
Inflammatory Bowel Disease (Crohn's Disease or Ulcerative Colitis): These conditions can cause chronic abdominal pain, changes in bowel habits, and other systemic symptoms.