Rheuma Case: 68-year-old Woman with Knee Pain

00:00 Hello. Now we're going to talk about an approach to joint pain. So, our objectives for this next section is to highlight the key features that distinguish types of joint disease. We're going to describe broad categories of all the rheumatologic diseases that are covered in this section.

00:20 But let's start with a case. So a 68-year-old woman presents to your office with knee pain. Her past medical history is notable for dyslipidemia, obesity, and smoking. Initial vitals: Temperature of 37.2°C, heart rate of 67, and a blood pressure of 124/69. Not a lot of data yet. So when presented with a case like this, she may want to order some basic lab studies, maybe some specific antibodies, some x-rays, CT scans, MRIs, arthrocentesis, a muscle biopsy, gram stain, maybe microscopy with polarized light. My oh my! That's a lot of diagnostic testing which could be quite costly, time consuming, perhaps invasive, and ultimately can yield a lot of false positives.

01:09 So we need a better approach to trying to hone in on our differential diagnoses in a more cost effective and hopefully fruitful way. So for the next several slides, we're going to review an approach to honing in on our diagnosis. So let's sweep away all those diagnostic tests and go back into our case and get some more information. So what we're going to look at are these 4 factors. We're going to talk about time course, the pattern of joint involvement, evidence of inflammation, and talk about systemic involvement. So let's go back into our case. Now we see that our 68-year-old woman is presenting to the office with 2 days of knee pain. So, we know that the time course is relatively acute or subacute. On further questioning, we learned that she reports left knee pain accompanied by milder right wrist pain. So we've got 2 joints involved.

02:05 When we talk about the number of joints; monoarticular is 1 joint, oligoarticular means 2-4 joints are involved, and beyond 4 joints we would use the term polyarticular. So she has asymmetric oligoarticular joint involvement. Thirdly, on exam, we see that she has a hot swollen left knee and a warm right swollen wrist. So we know that she has some evidence of joint inflammation.

02:31 And fourthly, on the skin exam, we also note some unusual findings. There is a 10 cm x 8 cm pink, erythematous, slightly raised, bull's eye shaped plaque on her left flank. So, in light of the fact that there is more than 1 system involved in her presentation, we believe that she has systemic involvement involving the skin. So just from those 4 variables, we get a lot more information and we know what to ask for when confronted with this initially limited history. So based on this information, what's the most likely diagnosis? Well, gout shouldn't really involve other organs. It can, but very rarely and depicted here is a picture of uric acid crystals shown under polarized light with its classic negatively birefringent crystals. Rheumatoid arthritis shouldn't be acute. In this case, this patient had only 2 days of symptoms and we also tend to have more symmetric findings. Shown here is a picture of very advanced rheumatoid arthritis with some of the destructive articular changes. Thirdly, osteoarthritis, also shouldn't really be subacute. You tend to have more chronic indolent waxing and waning symptoms. And you also would not expect to have significant inflammation as we are seeing in our case. Shown here is just a picture of classic arthritis of the femoro-acetabular joint of the hip joint with some exposed bone, decreased joint spaces, and some synovial cyst. And lastly, Lyme disease. Well, we know that she has skin involvement and Lyme disease can certainly affect the skin amongst a number of other joints and so in our case all those variables put together tell us that Lyme disease must be our diagnosis.

04:22 Shown in this image is a picture of erythema chronica migrans which is the classic bull's eye rash associated with Lyme disease.