Musculoskeletal
Renal colic due to a kidney stone; Acute ureteral obstruction (from stone, blood clot)
Pyelonephritis, renal abscess; Perinephric abscess.
Renal ischemia
Gallbladder disease e.g. cholecystitis
Appendicitis
Diverticulitis
Other GI disease: pancreatitis, mesenteric ischemia, etc.
Chest disorders e.g. Pneumonia
Salpingitis
Herpes zoster
Influenza
Vessicoureteral reflux
Ureteral stricture
Polycystic kidney disease (PCKD)
Ruptured aneurysm
Trauma to the kidneys
Renal infarction
Renal Tumor: Renal cell carcinoma; Transitional cell carcinoma; Wilm’s tumor
Papillary necrosis
Loin pain hematuria syndrome
Costochondritis
Slipping rib syndrome
Iliocostal friction syndrome
Thinking through the differential diagnosis
Think anatomy. The kidneys (and ureters and bladder), ribs, and muscles are found in the flank area. Also think about thinks that refer pain to the flank area.
Further Reading
Bueschen AJ. Flank Pain. In: Walker HK, Hall WD, Hurst JW, editors. Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd edition. Boston: Butterworths; 1990. Chapter 182. Available from: https://www.ncbi.nlm.nih.gov/books/NBK292/