Alkaptonuric patient presenting with "black" disc: a case report.

Although intervertebral disc degeneration usually occurs in the natural course of alkaptonuria, detection of the disease by black disc material in a patient without any other sign of alkaptonuria is an extremely rare condition. The authors report a 45-year-old previously healthy female patient who was operated on for prolapsed lumbar disc herniation, and in whom the nucleus pulposus was discovered to be black intraoperatively. The alkaptonuria was diagnosed after histopathological examination of the black disc material. Elevated urinary concentration of homogentisic acid confirmed the diagnosis.