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Updated September 22, 2015.

Nearly 4% of adults in the United States are affected by gout, a disease characterized by deposition of monsodium urate monohydrate (MSU) crystals in synovial fluid (joint fluid) and other tissues. With the realization that existing criteria for the classification of gout was developed prior to the availability of advanced imaging, an international group of 20 investigators took on the task of updating the classification criteria.

An improved classification system is important for research advancement.

Classification Criteria for Gout

The updated criteria, which was released in September 2015, was approved by the American College of Rheumatology (ACR) and the European League Against Rheumatism (EULAR). According to the updated criteria:

A patient must have met the following initial criterion before any other criteria can be considered :

• At least one episode of swelling, pain, or tenderness in a peripheral joint or bursa

To be classified as having gout, without needing to consider any other criteria, a patient must have or ever have had:

• MSU crystals in a symptomatic joint or bursa or tophus

Without the presence of MSU crystals, the following criteria are to be considered.

Clinical criteria:

Pattern of joint or bursa involvement during symptomatic episodes: There are two categories of involvement:

• ankle or midfoot involvement as part of a monoarticular or oligoarticular episode, without involvement of the first metatarsophalangeal joint (score as 1) 

• involvement of the first metatarsophalangeal joint as part of a monoarticular or oligoarticular episode (score as 2)

Characteristics associated with symptomatic episodes: Erythema (redness and inflammation) over the affected joint; touching the affected joint or pressure to the affected joint is unbearable; difficulty walking or using the affected joint. If a patient has or ever had one of the three characteristics, it is scored as 1 -- two characteristics as 2, and three characteristics as 3.

Timing of episodes: The presence of two episodes (ever) is noted, regardless of anti-inflammatory treatment. Typically, during an episode, the most severe pain occurs within 24 hours, symptoms resolve within 14 days, and there is complete resolution of symptoms between symptomatic episodes. One typical episode is scored as 1, and recurrent typical episodes are scored as 2.

Clinical evidence of tophus: The presence of a subcutaneous nodule, often vascularized, typically present in the joints, ears, olecranon bursae, finger pads, or tendons is scored as 4.

Laboratory findings: 

Serum urate or uric acid, measured by the uricase method, is best measured at a time when the patient is not being treated with urate-lowering medications and when more than 4 weeks have passed after the onset of an episode. Regardless of timing:

• less than 4 mg/dl is scored -4
• 6 to 8 mg/dl is scored 2
• 8 to less than 10 mg/dl is scored 3
• 10 mg/dl is scored as 4

Also, synovial fluid analysis of a symptomatic joint or bursa should be assessed for MSU. If it is negative, the result is scored as -2.

Imaging:

If there is imaging evidence (via ultrasound or DECT/dual-energy computed tomography) of urate deposition in a symptomatic joint or bursa, it is scored as 4. If there is imaging evidence of gout-related joint damage (by utilizing conventional x-rays of the hands or feet) and at least one erosion is revealed, that is scored as 4.

Bottom Line - The Scoring

In this classification scoring system for gout, the highest possible score is 23. A score of 8 is enough to classify a patient as having gout.

<sub>Sources:

2015 Gout Classification Criteria. An American College of Rheumatology/European League Against Rheumatism Collaborative Initiative. Neogi T. et al. Arthritis & Rheumatology. Vol. 67, No. 10, October 2015.
http://www.rheumatology.org/Portals/0/Files/2015%20Gout%20Classification%20criteria.pdf</sub>