Degenerative arthropathy due to Alkaptonuria




Rare hereditary disorder of tyrosine and phenylalanine breakdown


Homogentisic acid enzyme deficiency

- accumulate Homogentisic Acid

- product of tyrosine breakdown


Homogentisic acid deposited in cartilage & other soft tissues

- polymerises 

- pathology probably due to a disruption of collagen cross links by metabolites of homogentisic acid




Urine turns dark on standing 

- also when alkalised

- hence the name


Sweat stains clothes


Cartilage & connective tissue stained grey

- brownish-black pigment in connective tissue

- calcified cartilage

- deposits in virtually all cartilages

- discs, sclera, skin



- early OA secondary to  brittleness 

- presents 4th decade 

- back pain then knees / shoulders / hips

- most common presenting complaint



- especially affects spine

- difficult to differentiate from ankylosing spondylitis

- dense calcification of discs with narrowing of intervertebral space