Can We Diagnose Gout Without Needling Our Patients?
Abstract & Commentary
By Allan J. Wilke, MD, MA, Chair, Department of Integrative Medicine, Ross University School of Medicine, Commonwealth of Dominica. Dr. Wilke reports no financial relationship to this field of study.
Synopsis: Use of simply obtained historical, physical, and laboratory data can distinguish gout from other forms of arthritis in many patients and avoid joint aspiration.
Source: Janssens HJ, et al. A diagnostic rule for acute gouty arthritis in primary care without joint fluid analysis. Arch Intern Med 2010;170:1120-1126.
The gold standard for diagnosing gout is identifying crystals of monosodium urate (MSU) in fluid aspirated from the affected joint. Despite this, we frequently diagnose gout without it. These researchers, who included primary care physicians and rheumatologists from the Netherlands, asked the question, "How valid is a diagnosis of acute gouty arthritis made by family physicians?" They then went a step further and developed a scoring rule to diagnose acute gout without an aspirate. This was a prospective diagnostic study. The subjects were 381 patients presenting consecutively to 93 family physicians (FPs) with the complaint of a single, acutely swollen, painful joint. The test was the FP's diagnosis of gout. There were no exclusion criteria. All patients were referred to the rheumatology department within 24 hours of presentation to the FPs' offices. At the specialist's office, the subjects were interviewed and examined, had blood drawn, and had the affected joint aspirated and examined for MSU crystals. If no other crystals (for instance, calcium pyrophosphate) were seen and if there was no evidence for a septic joint, the patients were followed for at least a year and completely reevaluated if there was a recurrence. The investigators were blinded to the FPs' diagnoses until they had completed their workups. The subjects averaged in age 57.7 years and were predominantly male (74.8%). MSU crystals were identified in 216 patients (56.7%). The sensitivity (SEN), specificity (SPE), positive predictive value (PPV), and negative predictive value (NPV) of the test are summarized in Tables 1 and 2.
After performing univariate analysis and multivariate logistic regression, variables were identified that independently predicted a diagnosis of gout: male gender, previous patient-reported arthritis attack, involvement of the first metatarsophalangeal joint (MTP1), hypertension (HTN) or ≥ 1 cardiovascular disease (angina pectoris, myocardial infarction, heart failure, cerebrovascular accident, transient ischemic attack, or peripheral vascular disease), beer consumption, serum uric acid level > 5.88 mg/dL, erythrocyte sedimentation rate (ESR) > 20 for men or > 30 for women, and presence of tophus. These variables made up the "best model given the data" and were used to judge the performance of models based on easily obtained data. The last variable, tophus, was 100% specific for gout. The other variables were all statistically significant at the P < 0.001 level. The model that the investigators finally chose had two other variables, joint redness (P = 0.002) and onset within 1 day (P = 0.42), data easily obtained during a primary care visit. Beer consumption and ESR were dropped. Table 3 gives the point value for each variable.
When this scoring tool was applied to the population, a total score of ≤ 4 ruled out gout in almost all subjects, and a score ≥ 8 identified > 80% of patients with gout. Gout was present in 30% of those individuals who scored > 4 and < 8. The authors recommend that these patients should have joint aspiration.
Commentary
First the caveats: All of these patients presented with monoarticular arthritis. While this is the most common presentation for gout, it can be polyarticular, especially in the elderly. You will have to decide if the population in the eastern portion of the Netherlands is similar to yours. The authors did not show the raw data of the performance of their tool on the diagnosis of gout, so we are left to assume that they performed the math correctly. They reference their on-line calculator (www.umcn.nl/goutcalc), but it gives a risk score from 0.0 to 1.0 without guidance at what level you should act.
I think it is premature to adopt this diagnostic tool. It really should be vetted in a few more settings and populations first. Assuming it proves valid, it could benefit both patients and physicians. While it appears we are very good at identifying gout when we see it (97% sensitivity), we have too many false positives. We start these patients on treatment for a condition they don't have and which isn't completely benign. If the tool can readily and reliably differentiate between those patients who are very likely and very unlikely to have gout, we can begin appropriate therapy, and for those patients who fall in the middle, we can arrange for joint aspiration for a definitive diagnosis.
I like the idea of multiple data points to diagnose gout. Depending on limited data can be misleading. For instance, you might be tempted to dismiss gout in a man with a red MTP1 (i.e., podagra) and a serum uric acid level of 6.0, because the normal range for men is 2.5-8.0 mg/dL. However, the tool gives this patient a score of 9.0, indicative of gout. Considering the serum urate level in isolation will lead you astray. Gout can occur with normal uric acid levels,1,2 and the vast majority of people with hyperuricemia do not develop gout.3
These researchers examined many candidate variables in the process of selecting the ones for their diagnostic score. Some of the items that weren't chosen (because they did not achieve statistical significance) include items that we generally consider to be risk factors: age, family history, diabetes mellitus, renal stones, recent joint trauma, obesity, and any alcohol consumption (although beer consumption was significant). They do not comment on this.
References
1. McCarty DJ. Gout without hyperuricemia. JAMA 1994;271:302-303.
2. Zhang W, et al. EULAR evidence based recommendations for gout. Part I: Diagnosis. Report of a task force of the Standing Committee for International Clinical Studies Including Therapeutics (ESCISIT). Ann Rheum Dis 2006;65:1301-1311.
3. Campion EW, et al. Asymptomatic hyperuricemia. Risks and consequences in the Normative Aging Study. Am J Med 1987;82:421-426.
Use of simply obtained historical, physical, and laboratory data can distinguish gout from other forms of arthritis in many patients and avoid joint aspiration.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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