Cauda equina syndrome secondary to long-standing ankylosing spondylitis.

Fourteen patients with cauda equina syndrome secondary to long-standing ankylosing spondylitis are described. The roughly symmetrical neurological deficits were very slowly progressive and began long after the onset of the spondylitis, usually well after the rheumatological symptoms had stopped. Eventually every patient had cutaneous sensory loss in the fifth lumbar and sacral dermatomes. All patients developed urinary sphincter disturbances of a lower motor neuron type. There was prominent loss of rectal sphincter tone, and all but 2 patients had bowel complaints, including incontinence and severe constipation. Seven patients had mild to moderate weakness in the lumbosacral myotomes. Seven patients had pain in the rectum or lower limbs. Electromyographic abnormalities were consistent with multiple lumbosacral radiculopathies. Myelography and computed tomographic scanning of the lumbosacral spine showed characteristic enlargement of the caudal sac and dorsal arachnoid diverticula that had eroded the laminae and spinous processes. Recognition of this syndrome, coupled with computed tomographic scanning of the lower spinal canal, allows one to omit myelography, a procedure that is difficult because of the associated spine abnormalities. Surgical intervention should be avoided.