141. Alcaptonuria with ochronosis

Alcaptonuria is a rare inherited metabolic disease in which absence of the enzyme homogentisic acid oxidase results in excessive amounts of homogentisic acid in the urine. If such urine is alkaline on voiding, is made alkaline, or is simply left standing, its color becomes brown to black throughout.

Ochronosis is the condition in which a brown-black pigment is deposited in connective tissues of the body, especially cartilage, and to a lesser extent, skin and sclera. In most cases, the pigment is a derivative of homogentisic acid, but in a few instances the pigment results from long-term contact with phenol compounds, from industrial contact with quinones, or from use of quinacrine.

The patient shown had the classic bluish discoloration of the cartilage in her ears (image 1), subtle bluish discoloration of the skin overlying the knuckles and tendons of her hands (image 2), and a bluish hue of the tip of her nose and of her teeth (image 3). She also had a typical ochronotic brown-black spot on her right sclera (image 4).

Radiographs of her spine (image 5) showed the telltale sign of ochronotic spondylosis—diffuse calcification of the intervertebral discs. And radiographs of her knees (image 6) showed characteristic degenerative changes in the cartilage, leading to narrowed joint space with advanced eburnation of the opposing bone surfaces.