Black knee—ochronotic alterations in alkaptonuria

Abstract

This article presents the case of a 53-year-old male patient born in Sri Lanka, who presented to the outpatient unit with the suspicion of empyema of the knee joint. Within the framework of knee arthroscopy, the diagnosis of ochronosis was made and later confirmed by histopathological biopsy. The alkaptonuria is caused by a homogentisate 1,2-dioxygenase deficiency and leads to an accumulation of homogentisic acid, a degradation product of tyrosine. This leads to the characteristic appearance of ochronosis with bluish-black deposits in the tissue (e.g. in connective tissue, sclera and ear cartilage) and a black coloration of the urine.