Alkaptonuria and lumbar disc herniation. Report of three cases.

Alkaptonuria is a rare metabolic disease caused by deficiency of homogentisic acid oxidase and characterized by bluish-black discoloration of cartilages and skin (ochronosis). The authors report the cases of three patients with lumbar disc herniation who underwent discectomy and in whom the nucleus pulposus was discovered to be black. Alkaptonuria was diagnosed after discectomy. Discal herniation requiring surgery is unusual in alkaptonuria, with only a few reports. The symptoms in the three patients disappeared after surgery and no symptoms were demonstrated on follow-up examination.