The initial site of the disease is in the low back in 35-57% of cases, and chronic lower back pain with insidious onset is the most characteristic early symptom. It usually appears at the age of 18-22 years and is a dull pain that is difficult to localize, often felt deep in the buttocks or sacroiliac region. It may start unilaterally or intermittently and gradually become persistent and bilateral over several months, with stiffness and pain in the lower back area. Early symptoms in some patients can be low back pain rather than typical hip pain, which can be severe and may also worsen with vigorous activity and cause low back sprains. The next most common early symptom is back stiffness, most often in the morning, which may be relieved by light activity or a hot shower. Maintaining a position for too long may increase back pain and stiffness. Patients often experience difficulty getting up in the morning, so that they have to roll over to the side of the bed and try not to bend over to relieve the pain. Sometimes patients may awaken from a deep sleep or may wake up during the night and need to walk around or move around for a few minutes before falling back asleep. Individuals may have no back symptoms or very mild symptoms. Other patients may present with low back stiffness, transient myalgia, or pressure points in muscle or tendon areas that are exacerbated in wet and cold environments and are easily misdiagnosed as fibromyalgia.