2015 Gout Classification Criteria: an American College of Rheumatology/European League Against Rheumatism collaborative initiative

Abstract

Objective: Existing criteria for the classification of gout have suboptimal sensitivity and/or specificity, and were developed at a time when advanced imaging was not available. The current effort was undertaken to develop new classification criteria for gout.

Methods: An international group of investigators, supported by the American College of Rheumatology and the European League Against Rheumatism, conducted a systematic review of the literature on advanced imaging of gout, a diagnostic study in which the presence of monosodium urate monohydrate (MSU) crystals in synovial fluid or tophus was the gold standard, a ranking exercise of paper patient cases, and a multicriterion decision analysis exercise. These data formed the basis for developing the classification criteria, which were tested in an independent data set.

Results: The entry criterion for the new classification criteria requires the occurrence of at least 1 episode of peripheral joint or bursal swelling, pain, or tenderness. The presence of MSU crystals in a symptomatic joint/bursa (i.e., synovial fluid) or in a tophus is a sufficient criterion for classification of the subject as having gout, and does not require further scoring. The domains of the new classification criteria include clinical (pattern of joint/bursa involvement, characteristics and time course of symptomatic episodes), laboratory (serum urate, MSU-negative synovial fluid aspirate), and imaging (double-contour sign on ultrasound or urate on dual-energy computed tomography, radiographic gout-related erosion). The sensitivity and specificity of the criteria are high (92% and 89%, respectively).

Conclusion: The new classification criteria, developed using a data-driven and decision analytic approach, have excellent performance characteristics and incorporate current state-of-the-art evidence regarding gout.

Figure 1

Flow chart of the study process. The major steps taken to develop the new American College of Rheumatology/European League Against Rheumatism criteria for classification of gout are outlined. SUGAR = Study for Updated Gout Classification Criteria.

Figure 2

Examples of tophus. The tophus is defined as a draining or chalk‐like subcutaneous nodule under transparent skin, often with overlying vascularity. Typical locations are the ear (A), the elbow (olecranon bursa) (B), and the finger pulps (C and D). Note the overlying vascularity in D.

Figure 3

Examples of imaging features included in the classification criteria. A, Double‐contour sign seen on ultrasonography. Left panel shows a longitudinal ultrasound image of the femoral articular cartilage; right panel shows a transverse ultrasound image of the femoral articular cartilage. Both images show hyperechoic enhancement over the surface of the hyaline cartilage (images kindly provided by Dr. Esperanza Naredo, Hospital Universitario Gregorio Marañon, Madrid, Spain). B, Urate deposition seen on dual‐energy computed tomography. Left panel shows urate deposition at the first and fifth metatarsophalangeal joints; right panel shows urate deposition within the Achilles tendon. C, Erosion, defined as a cortical break with sclerotic margin and overhanging edge, seen on conventional radiography of the first metatarsophalangeal joint.