A patient with ochronosis (alkaptonuria) may present with back pain which may be confused with ankylosing spondylitis.
Imaging features shared with ankylosing spondylitis:
(1) reduction in intervertebral disk space
(2) loss of lumbar lordosis
Imaging studies in ochronosis:
(1) sparing of the sacroiliac joint
(2) dense, wafer-like disk calcifications
(3) vacuum disks
(4) broad syndesmophytes
The diagnosis of ochronosis should be considered:
(1) if there is little or no response to appropriate therapy for ankylosing spondylitis
(2) ochronotic arthropathy, with involvement of knees and hips
(3) discoloration of the urine
(4) pigmentation of skin, sclera and/or connective tissue
(5) discoloration of clothing after sweating
