Inflammatory rheumatic diseases in patients with ochronotic arthropathy

Ochronotic arthropathy (OcA) refers to excessive homogentisic acid (HGA) deposition in the musculoskeletal system. Our current understanding of OcA is limited, as there are less than a thousand alkaptonuria (AKU) cases reported in the literature. Herein, we investigated the rheumatological manifestations of OcA in a group of adult AKU patients.

Adult AKU patients with symptoms suggestive of OcA were included. Patients underwent a detailed rheumatological assessment. Laboratory testing, including autoantibodies and radiological investigations such as conventional X-rays, and magnetic resonance imaging (MRI) were performed.

Eight out of 12 (66%) patients had symptoms consistent with OcA. The median age at OcA symptoms was 36 (27-48) years, and the presenting symptom was back pain in 87.5% of the patients. All patients had chronic back pain, and three (37.5%) had an inflammatory type of pain character. Radiographic sacroiliitis based on X-rays was present in 2 (25%) cases. MRI of the sacroiliac joints documented bone marrow edema in five (62.5%), and spinal MRI identified corner inflammatory lesions in three patients (37.5%). One patient (12.5%) had rheumatoid arthritis. Extra-articular involvement, including enthesitis (n = 1; 12.5%), interstitial lung disease (n = 1; 12.5%), and scleritis (n = 1; 12.5%), was also noted.

The frequent occurrence of OcA-related inflammatory manifestations in our patients contradicts the conventional concept of OcA as a non-inflammatory disorder. The activation of inflammatory pathways, possibly by the HGA products, may responsible for this condition.Significance and innovationsAbout three-fourths of adult ochronotic arthropathy (OcA) patients in our group had associated inflammatory disease.OcA associated inflammatory diseases were showing a severe phenotypeNearly half of the OcA patients required early prosthesis operations compared to their healthy counterparts.