A case of thoracic myelopathy secondary to alkaptonuric spondylosis

Alkaptonuria is a rare autosomal recessive metabolic disease of the aromatic amino acids phenylalanine and tyrosine. The disease is characterized by deficient homogentisic acid oxidase in the liver and kidneys and the subsequent excretion of homogentisic acid (HGA) in the urine [1, 2]. A high level of plasma HGA accumulates in the connective tissue, and its oxidation and polymerization lead to brown to black pigmentation, called ochronosis. Ochronosis is especially noted in collagen-abundant cartilaginous tissue, ligaments, and intervertebral discs [3]. Although the exact relationship between the extent of HGA deposition and degenerative changes in tissue has not been clarified, the large peripheral joints and spine are usually affected with advancing age [4].