Ankylosing spondylitis. A common cause of low back pain.

Ankylosing spondylitis should be a diagnostic consideration in young patients with back pain, particularly young men. Simple clinical methods can distinguish between back pain due to ankylosing spondylitis and back pain caused by other factors. Early diagnosis allows the clinician to prescribe anti-inflammatory therapy, to identify extra-articular involvement, and to provide counseling on the importance of maintaining proper posture. Perhaps more important, early diagnosis can avoid the costly and unnecessary diagnostic or therapeutic procedures that may be performed if back pain is misdiagnosed as mechanical.