Rheuma Case: 48-year-old Man with Fevers, R Knee Pain and Swelling

00:01 Okay we're gonna jump now into the topic of septic arthritis.

00:06 Here's the case: A 48-year old marketing consultant presents with fevers and right knee pain and swelling for the past 2 days.

00:14 Denies any recent trauma or obvious triggers.

00:16 No recent travels, no recent sexual activity nor any recent gastrointestinal infections.

00:22 He does report that he binge drinks and occasionally uses cocaine intravenously on the weekends when hanging out with his childhood friends.

00:30 He's gone hiking several times in the past few weeks.

00:33 A lot of different historical information there that may guide us when we're starting to generate a differential diagnosis.

00:40 He smokes about 10 cigarettes per day, he's divorced and not currently sexually active.

00:45 Family history, he has an uncle with inflammatory bowel disease.

00:48 We'll see if that's relevant or not.

00:49 And review of systems: no nausea, no vomiting, no diarrhea, no abdominal pain or hematochezia.

00:56 He does report however some malaise, and some fatigue.

00:59 So whenever reading a history and physical presented to you on a board question, it's gonna be really important to figure out why the authors of the questions are including or excluding certain features And in this case, there's a lot of excess information here for us to go through.

01:14 First, let's pick out the four most important variables.

01:16 Time course.

01:17 So it looks like this is a fairly acute presentation, it's only been there for about the past 2 days.

01:23 Pattern of joint involvement.

01:24 We're dealing with a monoarticular problem.

01:26 It's just the right knee and that's gonna help us when we're thinking about our differential diagnosis.

01:31 Thirdly, is there joint inflammation? This is a hot, swollen, tender knee - that's the textbook definition of what an inflamed joint looks like.

01:40 So yes, we have joint inflammation.

01:42 And fourthly, is there evidence of systemic involvement? Not a hundred percent clear but the patient is reporting fevers.

01:49 We have some malaise, some fatigue, so it looks like there probably is some sort of systemic process going on here.

01:55 Highlight in bold are several other useful pieces of information and on the next slide we'll talk about why those particular pieces are relevant.

02:03 So again, absence of GI infections, the presence of intravenous cocaine use, the binge drinking, recent hiking, lack of sexual activity, and family history of inflammatory bowel disease and again, those review of systems pieces as well.

02:18 So let's head into our differential diagnosis.

02:22 Non-gonococcal septic arthritis, Lyme disease, Gout, gonoccocal septic arthritis and reactive arthritis.

02:30 Now the bad news is that all five of these could be characterized by acute monoarticular arthritis with fevers and systemic involvement.

02:39 Some are certainly more inclined to have oligoarticular or polyarticular symptoms but they can all start off with a single joint.

02:48 So we're gonna need some more information and hopefully those details that we put in bold on the last slide will help guide us through.

02:53 So what are the features that will distinguish amongst these diagnoses? Okay, non-gonococcal septic arthritis.

03:01 The knee is the most common joint involved and typically it's MRSA or methicillin-resistant Staph. aureus that's gonna be the pathogen.

03:08 Because that's the most common pathogen, we think about what factors would lead somebody to become bacteremic and end up with bacteria in their joints.

03:16 So, injection drug use - he is using cocaine intravenously, that's gonna be a risk factor.

03:21 Similarly, prior surgery, any procedure that involves breaking the skin, underlying osteoarthritis, rheumatoid arthritis or gout.

03:29 Those things can all contribute to an increased risk of a non-gonococcal septic arthritis.

03:34 So we have to leave that one on our list for sure.

03:37 Lyme disease.

03:38 Turns out the knee is also the most common afflicted joint in Lyme disease.

03:43 So we've got to leave this one there as well.

03:45 His recent walk in the woods could certainly have exposed him to ticks.

03:49 What's missing though is the absence of a headache and he doesn't have any of that classic "bulls eye" rash or erythema chronicum migrans that we would look for with Lyme disease but nonetheless, not every patient presents with that.

04:01 So we'll have to keep that on the list as well.

04:03 Thirdly, gout.

04:05 Well, the most common joint for gout is the 1st MTP - that is the metatarsophalangeal joint of the big toe.

04:13 More common than the knee but absolutely, people can get gout in the knee.

04:17 He is relatively young for gout.

04:20 We're not giving the information that he's obese and they gave us a lot of other information, but he does drink alcohol.

04:26 He does not have CKD and men are more common than women to develop gout.

04:31 So we've got some things going for and some thing's going against gout We'll have to keep that on the list.

04:36 Fourth, gonococcal septic arthritis.

04:39 This is usually characterized by migratory polyarthralgias so multiple joints being painful and not necessarily having big, hot swollen joints.

04:49 More often do involve the small to medium-sized joints - the finger joints, the wrists, the ankles, and classically for gonococcal septic arthritis, or disseminated gonoccocal infection is another term that we would use, patients may have some pustules or vesicles on their palms or on the soles of their feet.

05:08 We'd expect the patient of course since we're talking about gonorrhea to have recent sexual activity, more common amongst young group, men and women for that reason, and for whatever reason, it is more common in women.

05:20 It doesn't seem like we have a lot going for gonococcal septic arthritis.

05:24 The last piece we'll look for is tenosynovitis which is inflammation of the synovial sheaths around tendons.

05:31 And again, we'll keep it on the list but it seems less likely based on the information that we have thus far.

05:37 Next on our list, reactive arthritis.

05:39 So this is one of the axial spondyloarthritides and it is characterized by lower extremity oligoarthritis.

05:46 So again, the knees, the ankles , not unlike what we have in our patient.

05:51 Such patients with the reactive arthritis have an antecedent genitourinary or gastrointestinal infection.

05:57 Our history specifically said he did not have any recent gastrointestinal infections.

06:02 The age is right though.

06:03 Typically, ages range from 20-40 and the other things we'll be looking for are enthesitis.

06:09 That's basically inflammation of the insertion of a tendon into a bone, most commonly at the Achilles tendon or perhaps at the elbow.

06:17 Eye symptoms - anterior uveitis would be a concern.

06:20 Lower back pain, urethritis, and dermatitis.

06:24 One of the classic things you might hear when you're thinking about reactive arthritis is, "can't see, can't pee, can't climb a tree" It rhymes - it's easy to remember.

06:33 And lastly, the typical HLA pattern for folks with reactive arthritis as well as the other axial spondyloarthritides would be an HLA-B27 haplotype In our case, not a lot going for that but we should really keep it in our list for now.

06:50 So let's look at the physical exam.

06:52 He is in fact febrile, temperature is 37.9 degrees Celsius.

06:57 heart rate's 88, blood pressure's okay.

06:59 He is thin, fit-looking, again, that's gonna steer us away from the gout question, no acute distress.

07:05 He has no scleral or conjunctival injections, so it's good to see there's no eye involvement at this time.

07:11 And unsurprisingly, the right knee is grossly swollen and hot.

07:15 There's no other joints involved.

07:17 No tenderness to palpation of the Achilles tendon or the plantar fascia And you know why they specifically mentioned that.

07:23 It's again talking about reactive arthritis which is prone to having enthesitis at insertion points of tendons into bone.

07:31 In the skin, perhaps presumably because of his injection drug use with cocaine, he has some track marks in his left antecubital fossa.

07:39 There's no vesicles or papules or erythema chronicum migrans.

07:42 no keratoderma blenorrhagicum or circinate balanitis.

07:46 Now those last two very complicated Latin terms are referring to some of the classic findings that we might see with reactive arthritis as well.

07:54 The lack of ECM steers us away from gout.

07:56 And the absence of vesicles or papules is gonna steer us away from disseminated gonoccocal infection cause you'd see those lesions on the hands.

08:05 Finally, we'd get an arthrocentesis, and this is where the money is.

08:08 This will help us to really understand what is happening.

08:10 We have yellow, opaque synovial fluid.

08:13 The white cell count is 72,000 white blood cells which is polymorphonuclear predominant, 82% There's no crystals, the gram stain is negative and the culture is pending.

08:26 So, let's interpret that synovial fluid cell count.

08:29 This is a gradient from less than 2,000 to greater than 80,000 white blood cells in the synovial fluid and the higher up you go, the more inflamed unsurprisingly the joint is.

08:40 So typical things like osteoarthritis with a little bit of an acute synovitis and OA, you really shouldn't have more than 2,000 white blood cells, you might only have a few hundred.

08:51 As you move up to a rheumatologic disease and an inflamed joint from say lupus or rheumatoid arthritis, you can have 2 to 20,000 white blood cells Gout's gonna be considerably more, it's really an abundant inflammatory response initially with macrophages and monocytes but then there's this recruitment of polymorphonuclear cells so 20,000-80,000 cells would be pretty typical.

09:13 And once you get above 80, you're really thinking about septic arthritis.

09:18 Mind you, you don't need to have 80,000 cells to think septic arthritis.

09:21 Our patient has 72,000 so we should absolutely be keeping this on our differential.

09:26 It's right in that ballpark between gout and infectious arthritis.

09:29 One thing we can say is that with a count of 72,000 we can safely take reactive arthritis and Lyme off of our list.

09:38 Okay so now, revisiting our differential diagnosis, we can safely take Lyme disease and reactive arthritis off the list based on the relatively elevated cell count.

09:48 And now let's look at the remaining three.

09:50 I mean, gout is possible but his relatively young age, and most importantly the absence of any crystals is gonna steer us away from that diagnosis.

09:59 So I'm comfortable taking that one off.

10:01 Now we're left with non-gonoccocal and gonococcal septic arthritis.

10:05 So, now how are we gonna distinguish amongst these last two remaining diagnoses, non-gonococcal and gonococcal septic arthritis? Well, looking at the gonococcal one first, he doesn't really have migratory polyarthralgias.

10:19 He's got mostly involvement of his knees, he doesn't have the pustules or vesicles and most importantly he completely denies any recent sexual activity.

10:27 Things really aren't going for that diagnosis.

10:29 In contrast, for non-gonococcal, he's using injection drugs.

10:33 He's got the track marks to prove it.

10:35 He's likely to have gotten Staph. aureus into his bloodstream.

10:39 It's fairly elevated at this point and again the knee is the most common joint involved.