The presence of monosodium urate monohydrate crystals in a symptomatic joint, bursa, or tophus is sufficient to diagnose gout, according to new gout classification criteria from the American College of Rheumatology and the European League Against Rheumatism.
When symptomatic urate crystals are missing, other signs and symptoms are considered and scored; a score of 8 or more constitutes gout. “The threshold chosen for this classification criteria set yielded the best combination of sensitivity and specificity,” at 92% and 89%, respectively, and outperformed previous classification schemes, said the authors, led by Dr. Tuhina Neogi of Boston University.
Dr. Tuhina Neogi
To qualify for gout, patients must first have at least one episode of swelling, pain, or tenderness in a peripheral joint or bursa. They get a score of 1 if that happens in the ankle or midfoot, and a score of 2 if it involves a metatarsophalangeal joint. If the affected joint is red and too painful to touch and use, patients get an additional score of 3. Chalklike drainage from a subcutaneous nodule in a gout-prone area, and serum urate at or above 10 mg/dL, both get a score of 4. Imaging of one or more gout erosions in the hands or feet also gets a score of 4 (Arthritis Rheumatol. 2015 Oct;67[10]:2557-68. doi: 10.1002/art.39254).
Overall, the criteria incorporate clinical, laboratory, and imaging evidence. A web-based calculator makes the scoring easy.
“Although MSU [monosodium urate monohydrate] crystal results are extremely helpful when positive, they are not a feasible universal standard, particularly because many potential study subjects are likely to be recruited from nonrheumatology settings. We aimed to develop a new set of criteria that could be flexible enough to enable accurate classification of gout regardless of MSU status,” the authors said.
“This classification criteria set will enable a standardized approach to identifying a relatively homogeneous group of individuals who have the clinical entity of gout for enrollment into studies. The criteria permit characterization of an individual as having gout regardless of whether he or she is currently experiencing an acute symptomatic episode and regardless of any comorbidities,” they said.
The hope of the work is to facilitate a better understanding of gout and speed development of new trials and treatments. The criteria will “help to ensure that patients with the same disease are being evaluated, which will enhance our ability to study the disease, including performing outcomes studies and clinical trials,” Dr. Neogi said in a written statement.
Previous gout classification criteria were developed when advanced imaging was not available. “Additionally, the increasing prevalence of gout, advances in therapeutics, and the development of international research collaborations to understand the impact, mechanisms, and optimal treatment of this condition emphasize the need for accurate and uniform classification criteria for gout,” according to the statement.
The new criteria are based on a systematic review of the literature on advanced gout imaging; a diagnostic study in which the presence of MSU crystals in synovial fluid or tophi was the gold standard; a ranking exercise of paper patient cases; and a multicriterion decision analysis exercise. The criteria were then validated in 330 patients.
The work was supported in part by the National Institutes of Health, the Agency for Healthcare Research and Quality, and Arthritis New Zealand. Numerous authors reported receiving consulting fees, speaking fees, and/or honoraria from companies that market drugs or specialty foods for gout.