Nephrolithiasis (Kidney Stones): This condition often presents with severe, crampy pain that starts in the flank or lower back and radiates to the lower abdomen or groin. The pain can be accompanied by nausea, vomiting, and urinary frequency or urgency.

Pyelonephritis: An infection of the kidney, which can cause flank pain that radiates to the lower abdomen and is often accompanied by fever, chills, and urinary symptoms.
Diverticulitis: Inflammation of the diverticula in the colon, which can cause lower abdominal pain that may radiate to the back, accompanied by changes in bowel habits and possible fever.
Appendicitis: Although classically presenting with right lower quadrant pain, some cases can have a more generalized or mid-abdominal pain that radiates to the back, especially if the appendix is retrocecal.
Gastroenteritis: Inflammation of the stomach and intestines, usually due to infection, which can cause generalized abdominal pain that may radiate to the back, along with nausea, vomiting, and diarrhea.

Abdominal Aortic Aneurysm (AAA): A potentially life-threatening condition where the aorta enlarges, which can cause severe back or abdominal pain. It's crucial to consider this diagnosis, especially in older patients with risk factors such as smoking or hypertension.
Pancreatitis: Inflammation of the pancreas, which can cause severe, persistent pain in the upper abdomen that radiates to the back, often accompanied by nausea and vomiting.
Ectopic Pregnancy: A pregnancy that develops outside the uterus, which can cause lower abdominal pain that may radiate to the back, along with vaginal bleeding and missed periods. This is a critical diagnosis to consider in women of childbearing age.
Ovarian Torsion: A condition where the ovary twists around its ligaments, cutting off blood supply, which can cause severe, sudden lower abdominal pain that may radiate to the back.

Intestinal Obstruction: A blockage that prevents normal flow of the products of digestion, which can cause severe abdominal pain that may radiate to the back, along with nausea, vomiting, and constipation.
Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease or ulcerative colitis, which can cause chronic abdominal pain that may radiate to the back, along with changes in bowel habits and possible weight loss.
Primary or Metastatic Tumors: Abdominal or back pain can be a symptom of various cancers, such as pancreatic, ovarian, or colon cancer, which are less common but important to consider, especially with persistent or worsening symptoms.