SLR - August 2015 - Allen Fung

The Validation Of A Diagnostic Rule For Gout Without Joint Fluid Analysis: A Prospective Study

Reference: Kienhorst LB, Janssens HJ, Fransen J, Janssen M. The Validation of a Diagnostic Rule for Gout Without Joint Fluid Analysis: A Prospective Study. Rheumatology. 2015 Apr;54(4):609-614

Scientific Literature Review

Reviewed By: Allen Fung, DPM
Residency Program: Wyckoff Heights Medical Center

Podiatric Relevance: Gout is a medical condition in which defective metabolism of uric acid causes deposition of monosodium urate crystals leading to inflammatory arthritis, swelling, erythema, and pain especially in joints. It is a common pathology podiatrists encounter as it has a propensity to manifest at the 1st MPJ, ankle, and other lesser joints of the foot. The gold standard for the diagnosis of gout is the detection of monosodium urate crystals in the joint fluid aspirate via polarized microscopy.  In some facilities, including the office setting, joint fluid analysis is not readily available and the diagnosis of gout is made clinically. This article describes a novel diagnostic rule comprised of seven variables which can be used to attain greater accuracy in the diagnosis of gout without joint fluid analysis.

Methods: Three-hundred ninety patients with signs and symptoms of monoarthritis at their first visit who presented to Rijnstate Hospital, Arnhem, Netherlands from January 1, 2011 to May 8, 2013 were included in the study. Patients who were previously diagnosed with gout were excluded. Data for all seven variables of the diagnostic rule were collected. These variables are male sex (score 2 points), previous patient-reported arthritis attack (score 2 points), onset within one day (score 0.5 points), joint redness (score 1 point), involvement of the 1st MPJ (score 2.5 points), hypertension or one or more cardiovascular diseases (angina pectoris, myocardial infection, heart failure, cerebrovascular accident, transient ischemic attack or peripheral vascular disease (score 1.5 points) and serum uric acid > 5.88 mg/dL (score 3.5 points). All patients subsequently had the affected joint aspirated, and the joint fluid analyzed under a polarized microscope for monosodium urate crystals. The physicians who collected data on the variables of the diagnostic rule and who performed the joint fluid analysis were blinded for the total score. In cases where no joint fluid could be collected during arthrocentesis, the patient was considered to not have gout. When joint fluid analysis did not identify monosodium urate crystals, additional clinical and laboratory tests were used to diagnose or exclude other forms of arthritis, including the identification of other joint fluid crystals, IgM RF and anti-CCP antibodies, ANA, anti-streptolysin titer, anti-DNase B, Borellia IgM and IgG antibodies and x-ray evaluation. In the case of an unspecified arthritis, the patient was followed up for any new episode of arthritis and a joint aspirate was obtained then. If monosodium urate crystals were identified, the patient was retrospectively classified as having gout.

Results: Three-hundred ninety patients in this study had a mean age of 61 years old and 70 percent of them were male. The affected joints included the 1st MPJ (29 percent), knee (26 percent), ankle (17 percent), wrist (10 percent), elbow (4 percent), hallux IPJ (4 percent), hand PIPJ (3 percent), and other joints (7 percent). Monosodium urate crystals were found in joint fluid analysis in 56 percent of patients, 22 percent fulfilled criteria for other rheumatic diseases, and 22 percent were diagnosed with unspecified arthritis. The mean total scores of the diagnostic rule were 8.6 in the gout group and 5.2 in the non-gout group. Utilizing the Hosmer-Lemeshow goodness-of-fit statistical test and the receiver operating characteristic curve for the diagnostic rule, it was determined that a total diagnostic rule score of ≥ 8 points has a positive predictive value of 0.87 for gout and ≤ 4 points has a negative predictive value of 0.95.

Conclusion: The diagnostic rule and the seven variables as described in this paper is a useful, more accurate, and easy-to-use method to aid the clinician in ruling in or ruling out the diagnosis of gout without joint fluid analysis compared to clinical determination based on the patient's signs and symptoms alone. Use of the diagnostic rule increased the positive prediction value (PPV) of clinical diagnosis from 0.64 to 0.87 and the negative predictive value (NPV) from 0.87 to 0.95. The predictive values for clinical diagnosis of gout (PPV 0.64 and NPV 0.87) have been determined by the authors in another study in 2010 and are referenced in this article. Although there is no substitute for joint fluid analysis as the gold standard in the diagnosis of gout, use of the diagnostic rule is an excellent alternative to aid the clinician in diagnosis especially when joint fluid analysis results are not readily available. Furthermore, the diagnostic rule provides a non-invasive alternative to diagnose gout with high accuracy without performing a joint aspiration to a highly sensitive and painful joint which is oftentimes difficult to locally anesthetize. In cases where the diagnostic rule does not indicate gout, we can then perform collect joint aspirate to rule out other etiologies.

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