Synovial fluid analysis widely underused to confirm gout.
"We all know it's a common habit not to look for crystals," he said. "What I think we should consider is how we as experts can justify using standards that are clearly below the best. I don't think we can."
It's beyond debate that the only sure way to diagnose gout is to identify monosodium urate or calcium pyrophosphate dehydrate crystals in aspirated synovial joint fluid. Atypical cases of gout will be missed by failure to do so. A number of other conditions can mimic gout, including rheumatoid arthritis, infection, bone tumor, septic arthritis, and tenosynovitis. But if crystals cannot be identified in synovial fluid obtained from a swollen joint, it's extremely unlikely that a patient has gout.
"I think that in gout, crystals are always present, although they may be very, very few," according to Dr. Pascual, professor of rheumatology at the University of Alicante (Spain).
Yet surveys show that most rheumatologists don't routinely perform synovial fluid analysis, opting instead to hang their diagnosis on clinical features and demonstration of hyperuricemia.
There are a number of reasons for this casual, rather sloppy practice, Dr. Pascual continued. It has a long tradition. It is permitted by shortsighted American College of Rheumatology diagnostic criteria, which allow the diagnosis of gout without demonstration of crystals. Moreover, many rheumatologists mistakenly shrug off gout as being a minor disease where a missed or delayed diagnosis is of little import.
If referring physicians understood that demonstration of crystals in synovial fluid is the definitive means of diagnosing gout and that most rheumatologists don't utilize this procedure, they would lose respect for the specialty. "They might think that we are lax about evidence-based medicine or aren't well trained," Dr. Pascual observed at the meeting, which was sponsored by the European League Against Rheumatism.
There is a common misperception among rheumatologists that analysis of synovial fluid for crystals isn't a reliable technique. In fact, Dr. Pascual said, it is quite consistent and reproducible. He and his colleagues demonstrated as much in a recent study in which they briefly trained four residents in crystal detection and identification, then presented them with 64 synovial fluid samples, half of which contained crystals.
In the trainees' hands, synovial fluid analysis for identification of the needle-shaped, negatively birefringent crystals of monosodium urate had 95% sensitivity and 97% specificity. The test's sensitivity for identification of calcium pyrophosphate dehydrate crystals was 93%, with 92% specificity (Ann. Rheum. Dis. 2005; 64:612-5).
"The residents became quite confident in crystal identification after looking at about 20 samples with expert assistance," Dr. Pascual recalled.
Indeed, a physician can master the basics of crystal identification in synovial fluid samples in a 1-2-hour workshop. Dr. Pascual directed several such workshops during the Vienna conference.
The only laboratory equipment required for crystal analysis is a compensated polarized light microscope, a relatively inexpensive piece of office gear. Just as hematologists routinely look at bone marrow themselves rather than delegating the task to a technician. Dr. Pascual believes rheumatologists should take a hands on approach to synovial fluid crystal analysis. "I have a scope fitted with polarizing filters in my laboratory. It has been enormously helpful," he said.
Crystals will be present even after an acute gout attack is over. Indeed, their stability and high degree of organization is such that crystals remain in the joint for months to years after hyperuricemia has been brought under control. The higher the load of crystals, the longer they take to completely dissolve. But eventually they do disappear.
BY BRUCE JANCIN
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|Publication:||Internal Medicine News|
|Date:||Sep 15, 2005|
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