The disease is most often seen in adolescent males and has an insidious onset. Early symptoms are dull pain in the lower back, buttocks and medulla, with stiffness or sciatica. The pain is intermittent and mild at the beginning, and the disease is prolonged and can become persistent or even more severe after several years. Sometimes it can occur in the higher back, shoulder or peripheral joints, but soon the lower back symptoms can appear. Patients often feel that their symptoms are worse in the morning and after a long day at work, and that they worsen in cold and wet weather. Other patients first present with unexplained iritis, generalized fatigue, anorexia, weight loss, and low-grade fever. The symptoms are mild at first, making early diagnosis difficult and the cure rate low, and can be teratogenic at later stages.