BACKGROUNDAlkaptonuria or ochronosis is a rare autosomal recessive disease (prevalence from 1:19,000 to 1:1,000,000) that results from a mutation that causes a defect in the homogentisic enzyme 1,2-dioxygenase, causing blockage in the tyrosine metabolism cascade and accumulation of homogentisic acid. This substance is deposited in collagen-rich tissues, giving it a brown hue and making it fragile. It causes joint degeneration, rupture of tendons and muscles, darkening of the urine and skin, eye involvement and deterioration of heart valves.
CASE REPORTA female patient, 42 years old, has suffered a sudden pain in her left knee during a volleyball game and was submitted to radiography and magnetic resonance imaging exams. The orthopedic team opted for surgical conduct of tenorrhaphy of the left quadriceps tendon. During the procedure, a black color was noted at the distal insertion site of the quadriceps tendon, a stiffened tendon and the trochlea and patella cartilage were dark in color (greyish). The biopsy result confirmed the diagnostic hypothesis of ochronosis, and she was referred for rheumatological follow-up. In March 2022, she attended with the rheumatologist with requested tests: CRP 4.4 mg/mL, ESR 40 mm/h, 24-h urine homogentisic acid dosage: positive, nonreactive ANA, left shoulder ultrasound: supraspinal tendinopathy. Thus, the patient was oriented to maintain a restricted diet in precursor amino acids (phenylalanine and tyrosine) with referral to a nutritionist, physiotherapy for left supraspinal tendinopathy, reduction/moderation of physical activity with impact to the shoulders, and requested biopsy of the cutaneous lesion in the fingers, besides dosage of vitamins (C, D, B 12 ) and follow-up of inflammatory tests.
CONCLUSIONAlkaptonuria is a rare disease that manifests itself predominantly with osteoarticular degenerative manifestations, and multidisciplinary joint orthopedic, nutritional, and rheumatologic follow-up is very important.
