A22-year-old man is evaluated in the office for a 12-month history of gradually worsening low back stiffness that is present for 2 hours after awakening in the morning. he has significant fatigue but no fever, chills, night sweats, or weight loss. he does not have pains in the peripheral joints but does have bilateral buttock pains throughout the day on sitting. one year ago, he also had a 2-week episode of uveitis of the right eye, which responded to corticosteroid eye drops. on physical examination, vital signs are normal. he appears healthy but walks with a mild forward bending of his spine. deep pressure and palpation of the lumbar spine in the midline and both sacroiliac joints elicits tenderness. chest expansion in the fourth intercostal space is 2 cm (normal 5 cm), and he can only reach the mid calf region when attempting to touch his fingers to the floor.