Black colored intervertebral disc; ochronosis: A case report

Abstract

Ochronosis is a syndrome caused by the accumulation of homogentisic acid (HGA) in connective tissues. The phenomenon was first described by Rudolf Virchow in 1865. Defective production of homogentisate 1,2-dioxygenase results in the accumulation of HGA, a tyrosine degradation product, in the bloodstream. Large quantities of HGA are excreted daily in the urine, where it oxidizes to benzoquinones, which in turn form the melaninlike polymers that cause the discoloration of urine. Accumulation of HGA and its metabolites in tissues causes ochronosis. [1] The word ochronosis refers to the dark bluish discoloration of connective tissues including the sclera, cornea, auricular cartilage, heart valves, articular cartilage, tendons and ligaments. The embedded pigments also form cross-linkages with pigment depositions in adjacent fibers, stabilizing and reducing the elastic recoil of the fibers. This results in hardening of elastic structures increasing their rigidity and brittleness. Once ruptured, the exposed pigments cause a foreign body reaction and inf lammation. This pigment deposition also invokes deposition of hydroxyapatite, the mineral responsible for bone calcification, further hardening the connective tissue. The condition is most often associated with alkaptonuria but can occur from exogenous administration of phenol complexes like hydroquinone.