TAMPA, Florida—More than half of gout patients with high uric acid levels but normal plain radiographs already have early stages of joint damage, and this is more readily detected using magnetic resonance imaging (MRI) than using ultrasound (US) imaging, John D. Carter, MD, and colleagues report early online in Rheumatology.¹ Dr. Carter is in the division of rheumatology at the University of South Florida, Tampa, FL.

”Our most important finding was that more than half of patients with normal x-rays had skeletal damage of the index joint on MRI. This was the primary endpoint. However, I think the most interesting (and surprising) finding was that ~50% of all these subjects had synovial pannus,” Dr. Carter told Musculoskeletal Report. “It is important to remember that these MRI's and US's were obtained during intercritical gout (i.e. asymptomatic). This suggests a large percentage of patients have evidence of chronic ongoing inflammation even in the absence of clinical attacks.”

Gout MRIs showed 56% had joint erosions

The study included 27 patients with average disease duration of 6.8 years. Average serum uric level over the past 5 years was 8.09 mg/dL, and the average on the day of the first clinic visit was 7.96 mg/dL. Each had two clinic visits. At the first, a plain radiograph of the “index joint” was taken. This was the joint with the most acute attacks of gout. If the index joint was free of erosive damage, the patients returned for visit 2, at which MRI with contrast and US of the index joint were done, as well as MRI and US of an “asymptomatic joint” that had never had an acute gout attack. Erosive change on MRI and/or US of the index joint was the primary endpoint.

MRI showed that:

• 15/27 patients (56%) had erosions of the index joint
• 13/27 patients had synovial pannus
• 4/27 had bone marrow edema
• 3 had soft tissue edema

US detected erosions in the index in only 1 patient (4%). According to Dr. Carter, this might reflect the fact that the frequency of the US (8MHz) was rather low. He added, “Although the US readers were radiologists with experience in musculoskeletal US, US interpretation is a learned art. These results might also not apply to patients with more advanced gout.”

Gout damage begins early

“These data suggest that patients with gout suffer articular damage early in their disease course, even before that which is detected by normal radiographs. Also, the presence of synovial pannus in about half of these subjects suggests that gout is a chronic inflammatory arthritis that is occasionally "tipped over" to become clinically apparent,” Dr. Carter said.

Translating research into practice: imaging gout

Dr. Carter said that this study should not be taken to support routine MRI of all gout-affected joints. He added, “Also, we do not have data to know if these early changes that are only seen on advanced imaging should be aggressively treated with serum urate-lowering drugs and, if so, would such treatment improve long-term outcomes. These issues require further study.”

Fernando Perez-Ruiz, MD, of the Rheumatology Division at Hospital de Cruces in Vizcaya, Spain, told MSKreport.com that this study has several limitations. “Outcomes were not defined: there is no definition of tophus, pannus (that is for RA, not gout, "synovitis" is more “real"). If outcomes are not defined, results may not be reliable,” Dr. Perez-Ruiz said. He also noted that the researchers reported no analysis of outcomes in relation to flares or time from onset in each joint. “Are outcomes more frequent in more diseased joints?” he asked.

Similarly, Dr. Perez-Ruiz would have liked more detailed information on the MRI and US equipment and protocols used. He said that if the study was done comparing a good-quality MRI to a fair-quality US, the results may not be reliable. Dr. Perez-Ruiz said that MRI imagining is operator independent, while US as used in this study is operator-dependent, which raises questions about the qualifications of the US operators.

Dr. Perez-Ruiz agreed with Dr. Carter that clinicians should not regard this study as the basis for adopting MRI as standard-of-care in gout patients with normal plain radiographs, although he does use both US and MRI to evaluate chonic synovitis, tophi, and structural changes in patients with severe gout. He would like to see future studies combine imaging with clinical trials or observational, controlled studies to provide evidence of clinical care.

Reference

1. Carter JD, Kedar RP, Anderson SR, et al. An analysis of MRI and ultrasound imaging in patients with gout who have normal plain radiographs. Rheumatology [epub ahead of print September 10, 2009].