Challenges in Gout Diagnosis Save

Um, hello. Uh, my name is Angelo Gaffo. I am a professor of medicine in the division of immunology and clinical rheumatology at the University of Alabama at Birmingham, and I am also the section chief of rheumatology at the Birmingham VA. I will be talking to you all today about a topic which I have always enjoyed a lot, which is gout — in this case specifically gout diagnosis.

Just as an introduction, gout is a quite prevalent condition, now estimated at 5% of United States adults, and its diagnosis is very tied up to understanding the clinical presentation of the condition. Gout primarily manifests itself as gout flares, and it's important to understand that gout flares are usually located in joints and periarticular areas, and I want to emphasize the latter. The gout flares happening around entheses and around bursae are also quite common, probably as common as those located intrinsically in the joints.

They have a preferential presentation in the lower extremities — very well-known podagra. The pain level associated with gout flares tends to be very high. Unless the patients come to your practice already medicated, there is usually a rapid escalation in the intensity of the pain from the moment the patient is pain-free until the moment the pain peaks. And gout flares are usually associated with joint swelling, warmth, erythema, especially in the small joints. Knowing this presentation helps you — puts you probably 60 to 70% of the way to diagnosing the condition.

A history of repeated flares like the ones I described is quite helpful. Gout usually — the natural history of the disease — implies an initial phase of flares like the ones I mentioned to you, that tend then to disappear after more or less 5 to 10 days, and then enters an intercritical period in which the patient is relatively back to their baseline level of pain, or lack thereof. Then, without the appropriate treatments, these flares become longer, become more frequent. These intercritical periods tend to shorten or go away completely, and then the patient can enter a chronic phase of chronic joint pain or swelling, or the presence of tophi — subcutaneous masses of monosodium urate. Some patients, rarely, can skip that initial phase of flares and go straight to a tophaceous phase. In our experience that is uncommon, but it certainly can happen.

So understanding this history, gathering this history during the clinical encounter, can again put you very, very well into diagnosing gout clinically, which is something that absolutely can happen.

So, uh, uric acid or serum urate — how do we use it in the diagnosis of gout? Serum urate can be informative for a diagnosis of gout. If you capture a patient during the intercritical phase, a large majority of patients who are not on urate-lowering therapies will be hyperuricemic. Hyperuricemia is technically defined as 6.8 milligrams per deciliter. Usually patients with gout will present with hyperuricemia levels of serum urate at seven, eight, or nine, or beyond. An elevated serum urate can support a diagnosis of gout but is not confirmatory, and a normal or low serum urate makes a gout diagnosis less likely.

So it's important to understand also that when a patient is presenting during a flare, serum urate can be lower, because the inflammatory milieu of the flare can stimulate the kidney tubules to excrete more serum urate, and sometimes serum urate can be one or one and a half points below what would be the real level that you will see during an intercritical phase. So do I check serum urate to help support the diagnosis of gout? I do, but I try to contextualize that number depending on whether the patient is in a flare or is not in a flare. It can be informative.

Of course, in rheumatology we love to review synovial fluid, and synovial fluid analysis is very important. It can help us differentiate gout from infection, from calcium pyrophosphate deposition disease. Obtaining gram stain, culture, and cell counts can all be quite informative. Looking under polarized light, you can see the needle-like structures that are monosodium urate crystals, which are negatively birefringent.

Do you always need crystal confirmation to diagnose gout? You don't. You can diagnose gout on clinical grounds without crystal confirmation. Sometimes patients will come to your visit in the intercritical phase without fluid. And although sometimes you can recover a small amount of fluid to examine in patients who are not having a flare, usually patients do not receive the proposal of having an arthrocentesis very well when they are actually not symptomatic.

I always obtain conventional radiographs — plain X-rays — because when I find overhanging edge erosions on plain radiographs, that is a very, very confirmatory finding for the
presence of gout in the right clinical context, a good history, and sometimes an elevated serum urate. You can see these overhanging edge erosions usually in the first MTP in the foot, or in some common in both areas by flares. And also you can sometimes find opacities which can be consistent with tophi that have had micro calcifications within them.

What we have been using more commonly now are ultrasound and dual energy CT scan. On the ultrasound you can sometimes see the double contour sign, which is a layer of monosodium urate overlaying the cartilage. Trained ultrasonographers can show that very well, and sometimes you can see erosions, aggregates, evidence of tophaceous deposits in the area around the joint. This is very supportive of a gout diagnosis, again in the right clinical context.

And finally, dual energy CT scan has been extremely helpful for us. It is relatively easy to obtain, is fast, no IV contrast, can provide that estimate of the tophaceous bulk, and is quite convenient and well accepted by patients in those intercritical phases when they are not having a flare. We can send them to the CT scanner and obtain a very informative scan for gout relatively fast. Problem is that sometimes it's not approved by insurance very easily, but in certain areas like our VA hospital, relatively easy to obtain.

So the messages that I want to encapsulate for you about gout diagnosis: the clinical presentation, basic laboratories including serum urate, and basic radiology can establish a diagnosis of gout in an important proportion of cases, and although crystal confirmation is desirable and quite helpful if you have it, it is not always necessary. And finally, advanced imaging techniques including ultrasound and dual energy CT scan can support the diagnosis, can be quite helpful, particularly useful during intercritical periods.

So I'm very happy for the invitation and the opportunity to talk about gout diagnosis, and we'll be with you the next time.