reveal degenerative changes involving the vertebrae and the intervertebral
discs, which show narrowing and calcification.
is the bluish-black discoloration of certain tissues, such as the ear
cartilage and ocular tissue, seen with alkaptonuria, a metabolic disorder.
It was defined by Virchow who described histologically the connective
tissue in alkaptonuria, given the cartilage's ochre, or yellow, hue under
the microscope. Alkaptonuria is a rare, autosomal recessive, metabolic
disorder caused by deficiency of homogentisic acid oxidase, the only enzyme
capable of catabolizing homogentisic acid. This deficiency results in
accumulation and deposition of homogentisic acid in cartilage, causing
the characteristic diffuse bluish-black pigmentation. Exogenous ochronosis,
in which bluish-black pigmentation of cartilage is noted iatrogenically
by exogenous agents, such as phenol, trinitrophenol, benzene and hydroquinone.
In alkaptonuria, the accumulation of HGA inhibits collagen cross-linking
by affecting a crucial enzyme in collagen synthesis, leading to a diminution
of structural collagen integrity. This results in ochronotic arthropathy,
which occurs in men aged in their fourth and fifth decades; women develop
similar complications in their sixth decade. The larger joints are most
affected with early calcification, narrowing and collapse of the intervertebral
discs. In addition to joint disease, there are reports suggesting increased
incidence of cardiovascular disease due to cartilaginous changes of vessel
Ashok Raghavan, Manipal Hospital, Bangalore