The aim of this study was to analyse the prevalence of occult destructive arthropathy in subjects with gout and normal plain radiographs by utilizing MRI and ultrasound (US).
The study consisted of two visits. At Visit 1, a plain radiograph of the 'index joint' was obtained. The 'index joint' was defined as a joint that has had the most acute attacks of gout historically. The index joint plain radiograph had to be free of erosive damage in order for the subject to qualify for Visit 2. At Visit 2, the subject had an MRI with contrast and an US of the index joint. Each subject also had an MRI and US of an 'asymptomatic joint'. The 'asymptomatic joint' was defined as a joint that had never experienced an acute attack of gout (determined by standard protocol). The primary endpoint was erosive changes on the MRI and/or US of the index joint. Secondary endpoints included erosive changes on the asymptomatic joint as well as bone marrow oedema (BME) (on MRI), synovial pannus (SP), soft tissue tophi (STT) or oedema (STE) on either the index or asymptomatic joint.
Twenty-seven subjects (26 males; 1 female) completed both visits. Their average age and disease duration were 55.1 years (range 21-75 years) and 6.8 years (range 0.25-25 years), respectively. The subjects' average serum uric acid level over the past 5 years was 8.09 mg/dl (range 4.1-12.8 mg/dl); their average on the day of Visit 1 was 7.96 mg/dl (range 4.6-13.9 mg/dl). The first MTP was the most common index joint (17) followed by the ankle (5), mid-tarsal (2), knee (2) and wrist (1). The knee was the most common asymptomatic joint (21) followed by the wrist (3), MTP (2) and ankle (1). All subjects had both MRIs; one subject refused the US. Out of 27 subjects, 15 (56%) had erosions on MRI of their index joint (P < 0.0001); only 1 subject (4%) had erosions identified in the index joint by US (P = NS). Regarding the secondary endpoints on the index joint, the MRI detected SP (13), BME (4), STE (3) and STT (0); the US detected SP (1), STT (1) and STE (0). Regarding the MRI of the asymptomatic joint, positive findings included SP (3), BME (3), STE (2) and erosions (1). There were no positive findings by US in the asymptomatic joint.
A large percentage of patients with gout and normal plain radiographs have occult destructive arthropathy that is only detected by advanced imaging such as MRI and/or US. However, MRI appears to be much more sensitive than US at detecting these findings.