Ochronosis is the musculoskeletal manifestation of alkaptonuria – a rather rare (one in 200,000 births) inherited disorder of protein metabolism characterized by an inability of the body to metabolize the amino acids tyrosine and phenylalanine. It affects especially the large joints (hip, knees and vertebral column) by a progressive degenerative arthrosis.
It was Scribonius who described the first known case of ochronosis in 1584. He mentioned a schoolboy who passed urine black as ink. In 1902, Albrecht and Zdareck discovered the link with alkaptonuria.
The incidence of alkaptonuria is 1 per million with the highest prevalence in Slovakia by inbreeding. [Laoussadi S., Menkes C.-J. Arthroses D'Etiologie rare. Rev. Rhum. Ed. Fr., nr 9 bis, Vol. 61, Nov. 1994]
The outward signs are the ocular (eye) and the skin pigmentations, the genitourinary calculi (stones) and cardiovascular ochronosis (especially the aortic valve). The symptoms mostly begin within the third or fourth decade.
The corner stones of diagnosis are the examination of the urine (black color) and the histopathological examination with hematoxylin-eosin staining confirming the ochronotic pigments in the tissues.
There is no cure for ochronotic arthropathy. The enzyme deficiency is as yet untreatable, but there is hope of gene therapy in the future. There only exists a symptomatic treatment: analgetics, NSAID, physical therapy, orthopedic supports and intra-articular corticoid infiltration, especially in the knee.
Although a very rare disease, the main outward symptom of ochronosis is black urine.
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