Diagnostic workup of gout

Robert McLean, MD, is a rheumatologist and associate clinical professor of medicine at Yale School of Medicine, USA.

Is the identification of crystals still a gold standard in diagnosing gout or can it be replaced by other modalities (ultrasonography, computed tomography)?

Some of the imaging studies are very helpful at showing gout crystals in joints. Plain x-rays don’t show gout crystals. They might show erosions, which happen much later in the course of gout. I think the advances in imaging have shown us [that with] ultrasound, computed tomography (CT) scan, and other really interesting modalities, we can see gout crystals and the load of uric acid that someone might have around that joint much better than ever before.

However, that’s just showing that there are uric acid crystals around the joint. The gold standard still for gout diagnosis—although we can’t always get it and we frequently cannot—is to actually see gout crystals in joint fluid. But even more than that, if anyone is hyperuricemic, they’re going to have gout deposited in their synovium, the joint lining. Little gout crystals may break off and may be floating around in their synovial fluid without causing any problem. Something causes the inflammatory cells to be activated and to then attack the gout crystals. The absolute gold standard is, when you remove fluid from a joint that seems to have inflammation that might be related to gout, to actually see under a polarizing light microscope a white blood cell that has a nice needle-shaped monosodium uric crystal piercing it in the middle, because it shows that the white cell has ingested the gout crystal.

Obviously, seeing inflammatory cells and seeing gout crystals floating around is highly suggestive and probably diagnostic, but there are situations where people are hyperuricemic and may have something else causing inflammation in their joint. Maybe they have an infection. There are multiple case studies over the years of people who seem to have coinfections of gout or pseudogout and an infection. Evaluating the joint fluid and—if it’s inflammatory—doing a culture is still really important, especially if people have diabetes or have some other condition that might predispose them to having an infection.