Rule Developed to Diagnose Gout Using Clinical Variables

From Medscape Medical News

Emma Hitt, PhD

July 22, 2010 — A diagnostic rule involving 7 clinical variables is useful in helping to determine which patients are at high risk for gout and should undergo further testing with joint fluid aspiration to test for the presence of monosodium urate (MSU) crystals.

Hein J. E. M. Janssens, MD, with the Department of Primary and Community Care, Radboud University Nijmegen Medical Center, in Nijmegen, the Netherlands, and colleagues reported their findings in the July 12, 2010, issue of the Archives of Internal Medicine.

The 7 variables, which the researchers describe as "easily ascertainable in primary care," include male sex, previous patient-reported arthritis attack, onset within 1 day, joint redness, involvement of the first metatarsophalangeal joint (MTP1), hypertension or 1 or more cardiovascular diseases, and serum uric acid level of more than 5.88 mg/dL.

"The presented diagnostic rule helps family physicians to select patients with high vs low probability of gout and to restrict the use of joint fluid aspiration to test for the presence of MSU crystals for patients with remaining uncertainty about the diagnosis," Dr. Janssens and colleagues write.

To validate the diagnostic rule, the investigators recruited 381 patients with monoarthritis. These patients had a mean age of 57.7 years, and 285 (74.8%) were men. MSU crystals were identified in 216 (56.7%) of the patients.

A total of 328 patients (86.1%) had an index test diagnosis of gout. Of these 328 patients, mean age was 58.0 (13.5) years, and 261 (79.6%) were men. MSU crystals was identified in 209 (63.7%) of these patients. On the reference test, the positive and negative predictive values of family physician diagnosis of gout were 0.64 and 0.87, respectively.

When the diagnostic rule was used (score ranging from 0 - 13), a score of 4 or less ruled out gout in almost 100% of patients. According to the researchers, in these patients, a differential diagnosis of rheumatoid arthritis, pseudogout, psoriatic arthritis, and reactive arthritis vs gout should be considered.

Among patients with a score of 8 or higher, gout was confirmed in more than 80%, indicating that gout-specific management options such as "systemic corticosteroid use (instead of nonsteroidal anti-inflammatory drugs), uric acid–lowering therapy if indicated, and evaluation of gout-associated cardiovascular and renal diseases" should be used. A false-positive diagnosis of gout was found in 17% of patients at this score range; by contrast, the family physician false-positive diagnosis rate was 36.3%.

A midrange score (> 4 to < 8) leaves uncertainty about the diagnosis. In these patients, of which approximately 30% had gout, "analysis of synovial fluid from the affected joint for the presence of MSU crystals should be considered if necessary for future management," the researchers suggest.

An online calculator for computing the diagnostic rule is available at the Nijmegen Medical Center Web site.

The study authors have disclosed no relevant financial relationships.

Arch Intern Med. 2010;170:1120-1126. Abstract