Undiagnosed Ochronosis Presented as Severe Osteoarthritis With Concomitant Osteoporotic Fracture

Ochronosis is a rare autosomal recessive disorder of tyrosine metabolism, leading to deposition of elevated levels of homogentisic acid in different parts of the body, especially in fibrous and cartilaginous tissues. The current study presents a case with delayed diagnosis and osteoporotic fracture in addition to severe osteoarthritis and calcification.
A 56-year-old female with low back pain and painful knees and hips referred to the center. Right hip arthroplasty was performed to manage her severe osteoarthritis. Although characteristic features of ochronosis such as urine darkening, subcutaneous pigmentation and degenerative ochronotic arthropathy resembling osteoarthritis were observed in this patient, surprisingly it remained unrecognized until the 5th decade. Bone mineral density showed that osteoporosis and zoledronic acid had started.
Usually, osteoarthritis is inversely correlated with the osteoporosis. Considering ochronosis as an osteoarthritis predisposing factor, the osteoporosis manifestation is not expected in such patients. However, in the current case, simultaneous osteoarthritis and osteoporosis fracture was observed, indicating unreliability of bone mineral density (BMD) in such patients. Authors believe that ochronosis could reduce bone quality, while its quantity might increase.