Rookies Quiz 4

Findings reveal degenerative changes involving the vertebrae and the intervertebral discs, which show narrowing and calcification.

Ochronosis

Ochronosis 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 walls.

Dr. Ashok Raghavan, Manipal Hospital, Bangalore