If you have back pain without a known cause, it may be referred from another body part or medical problem. Here are some medical conditions that can cause pain in the back in addition to their other symptoms.
Cancer or malignant tumor: Your back pain is worse at night, it wakes you up, no position decreases the pain, you may have had cancer before, you are likely over age 50, you may have rapid, unexplained weight loss.
Osteoporosis: You are likely an older woman, may have sharp pain in the mid-back or pelvis, may have dull pain which decreases when you lie down, you may have fallen recently.
Abdominal Aortic Aneurysm: You are likely over 50 years old, have abdominal pain in addition to back pain, and you can feel a lump in your abdomen.
Pancreatitis or cancer: You have stomach pain which spreads to the back, you have fever, nausea/vomitting, have lost weight and notice fat in your stool.
Penetrating or perforated duodenal ulcer: You have stomach pain which spreads around to your back.
Fibromyalgia: You are likely a young or middle-aged woman, you have pain throughout your body, you have difficulty sleeping, you feel continually tired.
Scoliosis: Your spine curves toward one side, you may feel like one shoulder is much lower, your back does not look symmetrical.
Nephrolithiasis: You may have abdominal pain which spreads around to your back, you may have groin pain, you have bloody urine.
Pyelonephritis: You have pain to the touch on one side of your low back, you have a fever, and you have difficulty urinating.
Prostatitis: You are likely over age 30, you have difficulty urinating, you have back pain and perineal pain.
Endometriosis: You are a young or middle-aged woman, you have pain in the pelvis and back.
Pelvic inflammatory disease: You are a young woman, you are sexually active, you have a fever and difficulty urinating.
Ectopic pregnancy: You have pain in your back and abdomen, you had a positive pregnancy test.
Brotzman SB, Wilk KE. Clinical Orthopaedic Rehabilitation, 2nd ed. Mosby: 2003. Page 562. Table 9-2: “Conditions That May Mimic Musculoskeletal or Mechanical Back Pain.”