Acute low back pain secondary to retroperitoneal hemorrhage in an elderly man.

Acute low back pain is a common complaint heard in the emergency room and in a physiatrist's practice. It is important to rule out occult pathology in patients with an atypical presentation. In the case presented here, the patient was elderly, developed back pain without preceding trauma or lifting, had a history of easy bruisability, had a large ecchymosis, and had worsening back pain with bedrest. An abdominal aortic aneurysm was ruled out and the patient was discovered to have a large retroperitoneal hemorrhage. He was diagnosed with acquired hemophilia secondary to factor VIII inhibitors. This has implications for physicians who treat patients with acute low back pain. They must be alert to potentially life-threatening causes of low back pain.