Thursday, May 26, 2016

Septic hip or synovitis? Use ultrasound!

The presentation 
The parents said their 5 year-old boy was limping on his right leg for the past day. The don't think he had hurt himself, and my exam confirmed that his foot, ankle, leg, and knee were atraumatic, but his hip was painful to range. He could still eke out an antalgic gait on the right leg, though. 

He had a slight temperature elevation of 100.2 F (37.9 C), and labs showed a WBC of 11.8, and an ESR of 28.

Was this a septic hip? What was the next test?

"The best decision rule is Kocher’s criteria."
Some folks still recommend using Kocher's criteria to rule-out septic arthritis in the limping child. If the child is able to weight bear, has no fever, and WBC < 12, and ESR < 40, then the risk of septic arthritis was only 0.2% in Kocher's original study.

Problem is, these sorts of results are all tied up with the population being studied and the prevalence of septic hip. Subsequent studies have found that kids with Kocher score of 0 can still have a risk of septic arthritis that ranges from < 0.2% to 17%.
Sultan & Hughes
In my patient's case, the kid's "Kocher score" was zero. And if we had trusted in this score we might have missed a septic hip!  

Don't guess with Kocher - just look at the joint with ultrasound!
First, we looked at the left (contralateral) hip, seeing what normal should look like. Then we looked at the painful right hip. It wasn't subtle!

An anechoic space space in the hip joint > 5 mm is generally considered positive for effusion.

The live clips were even clearer:

IR was contacted, and we performed sedation for the aspiration. The aspirate from his hip was wildly positive; grossly purulent, with > 100,000 WBC/mL. The child was admitted, and did well.

Note: Case was modified slightly for teaching purposes.
Only in 2 respects: His WBC was actually trivially higher, at 12.2, and he couldn't bear any weight at all on the right leg. These are small differences, and further highlight the potential pitfalls in using indirect criteria like Kocher's.

Open-Access References:
Limping Child? Think LIMPSS.
Septic arthritis or transient synovitis of the hip in children: The value of clinical prediction algorithms

Tuesday, May 17, 2016

Bugs in the B-hive: Read the lung ultrasound in context!

Lung ultrasound is a great tool, as well as cheap and fast. Heck, the ease of grabbing a quick look at the anterior apices makes the "STAT portable chest X-ray!" seem downright disappointing.

Although not as disappointing as blowing $1 of your allowance on these.
A great use of lung ultrasound is to help suggest the etiology of acute dyspnea, mainly to distinguish acute pulmonary edema from other causes. The "BLUE protocol" of Lichtenstein has shown that certain lung ultrasound findings can be very accurate for acute edema.

Specifically, Lichtenstein found that "diffuse anterior B-lines with lung sliding" was 97% sensitive, and 95% specific, for cardiogenic pulmonary edema. So, if you have bilateral "B-hives," maybe we don't even need chest X-rays or BNPs!

Let's apply this to a case.
An elderly female was brought to the ED with apparently acute onset shortness of breath. The history was sketchy, owing to the patient's dementia, but EMS reported a room-air sat in the 80's, improved with oxygen. In the ED she was tachycardic, hypoxic, and (initially) afebrile. No JVD or pedal edema. 

Ultrasound scans of the bilateral thoracic apices and bases was performed immediately.

However, her heart appeared to be squeezing quite well...

... and her IVC did not appear particularly plethoric either:

This seemed highly atypical for systolic or diastolic heart failure, and so we started antibiotics, and deferred nitro or diuretics. She later developed a fever in the ED, vindicating our decision.

Interestingly, the ED CXR showed only a left-sided infiltrate:

After the resident intubated the persistently-hypoxic patient, I predicted that, based on the lung ultrasound, that this was actually a bilateral pneumonia, and that she would deteriorate dramatically in the next few days. 

And indeed, 2 days later, her status was worsening, and a CXR showed progressive infiltrates bilaterally:

What happened to "95% specific?"
I can't dive into the weeds of Lichtenstein's methods or results, but there were numbers in his article that suggested caution in adopting his BLUE protocol. Of the 68 patients with diffuse anterior B-lines, 6 were ultimately diagnosed with pneumonia. 

I'm not sure how this squares with the "95% specific" figure, with 9% of patients being incorrectly predicted as cardiogenic pulmonary edema. Nonetheless, don't get carried away with lung ultrasound, without taking account of the clinical context!

Open-Access Reference:
Relevance of lung ultrasound in the diagnosis of acute respiratory failure: the BLUE protocol.

Friday, May 13, 2016

PE with a negative CT: Basic & Bonus lessons.

 A healthy male came to the ED complaining of chest pain and exertional dyspnea, worsening over the past few days. He mentioned that it felt like “the time I had a PE.(That PE had been provoked by a lower-extremity fracture, and he had completed 6 months of anticoagulation without problems.) 

While the vitals and exam were unremarkable, the ECG suggested RV strain:

A bedside echo also supported RV strain,with the apical 4-chamber showing notable RV dilation and septal bowing.

A CT for PE was ordered. Even before he had left for the CT suite, however, enoxaparin was ordered. The patient, who had been reading quite a bit about diagnosing and treating PEs in the past few days (quite educated!), reasonably asked why treatment was being ordered prior to the test.

The Basic Lesson:

If the patient has a high probability of having a PE, there is still a 40% chance of PE if the CTA is negative.

In this case, the ED echo, along with the clinical and ECG data, assuredly defined this patient as very high risk for PE.  

Despite the high probability, the CTA was negative. However, a V/Q done the next day was interpreted as high probability for PE, with multiple areas of mismatch.  

So, the CTA is not the gold standard we often take it to be, and we need to be careful to avoid ruling-out VTE prematurely. Of course, patients who are truly high probability for PE are infrequently seen (only 6% of subjects in PIOPED II).

The Bonus Lesson:
Why the discrepancy? The answer was likely on the ED echo as well.

Color and continuous wave Doppler, were used to interrogate the tricuspid valve. Only a moderate degree of regurgitation was seen, but with impressive velocities. The RV inflow view is shown here:

The maximum velocity of the TR jet exceeded 4 m/s, suggesting a RV systolic pressure over 70 mm Hg. This is a bit high for an acute PE, and suggests instead that a chronic process is involved. And indeed, chronic PE is known to be poorly visualized by CTA, but well demonstrated on V/Q scans.