Black joint and synovia: Histopathological evaluation of degenerative joint disease due to Ochronosis

Ochronotic arthropathy is a rapidly progressive and disabling arthropathy predominantly encountered after the fifth decade of life, caused by homogentisate1,2 dioxygenase enzyme deficiency. As it is rare disease, the literature on histological findings is fragmented. We retrospectively re-evaluated histopathological findings in resection and/or curettage materials (5 hip joint, 4 knee joint, one hip joint synovium, one intervertebral disk and one paravertebral disk tissue) of seven ochronosis cases diagnosed between 1995 and 2013 in a single center. Necrotic brown chondroid detritus was present in all cases either in synovia or in subchondral area, some of which evoked giant cell reaction. Notably, brown pigmentation was prominent in upper middle parts of the articular cartilage but not that prominent in superficial parts and in osteochondral junction, almost stopping at the tide mark. Pigmentation was observed both in extracellular matrix and in cytoplasm either in granular or homogeneous fashion. Depositions were less prominent in osteophytic processes, regenerated cartilaginous areas and loose bodies. Almost all cases showed synovial detritic and inflammatory reaction, fibrillation, eburnation, and subchondral sclerosis. Disk degeneration and findings of ligament rupture were also observed. Histopathological diagnosis of ochronosis is not complicated given the unique “black coloring” of the affected tissues and it can easily be differentiated from other causes of detritic synovitis both clinically and histopathologically. However, there is no definitive cure for today and the reasons for late onset of arthropathy in disease course, and the mechanisms of tissue reaction to fragmented detritus remain elusive.