Pulmonary Embolism Workup

[docmd2010]

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so if u have a patient that u suspect a PE, of course the first thing u do is start heparin, but after that (let's say ekg's shows tachy, cxr is neg), what do you do? spiral ct or v/q scan? that's always confused me...when do you do a spiral ct for pe and when do you do v/q.



also, for foot/vertebral osteomyelitis, world says that the best test is MR, but i've done questions in kaplan (in a kid, is this different) that the best test for foot OM, the best test is a bone scan...

help please!

 

[medInUSA]

According to Conrad Fisher, Kaplan "USMLE Master the Boards Step 3"

page 109

Spiral CT is the standard to confirm the presence of a pulmonary embolus. The spiral CT has an excellent specificity. The sensitivity is not ideal. Thus the Spiral CT is test of choice if the X-ray is abnormal IF spiral CT is positive for PE, case closed, it means you got it. However if the Spiral CT is negative, it doesn't mean that you cannot have it.

For the V/Q scan has a much lower specificity than Spiral CT (in other words many more false positives)
Therefore for the V/Q to be accurate the X-ray must be normal. the less normal the X-ray the less accurate the V/Q scan (since the X-ray must rule out other conditions so that the combo of the X-ray and then the positive V/Q would have a higher Specificity)

thus overall according to Conrad Fisher Spiral CT is the standard.

 

[medInUSA]

for the second part of your question what do you mean by the "best test"

do you mean the best inital test, or do you mean the most accurate test?



the best inital test for a suspected osteomyelitis is an X-ray, showing elevation of the periostium (conrad fisher master the boards step 3 page 6)

the most accurate test is a bone biopsy and culture.


Now, if the X-ray is normal and the clinical suspicion is still high, you go the best second line test which is MRI. The MRI is FAR superior to bone scan . The bone scan is very poor at being able to distinguish between infxn of the bone and infection of the soft tissue above it.

The MRI and bone scan have equal sensitivity but the MRI has a much higher specificity.

"You must do a bone biopsy/culture to treat osteomyelitis appropriately

The Treatment is according to oranism:


For Staph: (the most common cause) If sensitive Oxacilin or Nafcillin IV for 4-6 weeks.
for MRSA Vanco, linezolid or daptomycin IV (CANNOT Use ORAL)

for gram negatives: (salmonella pseudomonas) this is the only form of osteomyeilitis that can be treated orally with quinolones (since quinolones concentrate in bone)

The sed rate is the best method for following the response to therapy.

 

[funshi baba]

I had the same PE question for my ER preceptor and he said Spiral CT. V/Q scan is being phased out especially in small hospital with less personel

 

[Scaredshizzles]

I had the same PE question for my ER preceptor and he said Spiral CT. V/Q scan is being phased out especially in small hospital with less personel

Yea, V/Q's are getting pretty rare, and as result, I imagine fewer people know how to read them. In any case, a contrast allergy or renal insufficiency might still be a reason to get a V/Q S.

 

[stookie]

According to UW, for osteomyelitis, you should do a bone scan for bones other than those in the feet and spine, MRI for spine and foot osteomyelitis, and bone biopsy for a negative blood culture. Anyone mind clarifying this?

 

[Scaredshizzles]

According to UW, for osteomyelitis, you should do a bone scan for bones other than those in the feet and spine, MRI for spine and foot osteomyelitis, and bone biopsy for a negative blood culture. Anyone mind clarifying this?

I've never read it put that way, but it makes sense. Feet and lower extremities are a common area to get cellulitis/soft tissue infections secondary to venous stasis or Diabetes related complications.MRI is better at distinguishing soft tissue around the bone from bone itself....MRI would make sense for the spine also if the only symptom you had was pain, considering the varyious etiologies possible.

 

[medInUSA]

According to UW, for osteomyelitis, you should do a bone scan for bones other than those in the feet and spine, MRI for spine and foot osteomyelitis, and bone biopsy for a negative blood culture. Anyone mind clarifying this?

I disagree, according to Conrad Fischer,(whom I quoted above), a bone biopsy should always be done (regardless of positive or negative blood culture), because it affects the management. You want to treat according to organism and its sensitivity (Which I talked about above).

As for the bone scan instead of MRI, for the feet and spine, I've never read that before, but I could see the logic.

 

[superocker]

what if you started the patient on antibiotics say for staph and he gets better
why would you want to subject the patient to pain (unless you are submitted to some masochistic desires of the patient)....
especially if cultures are positive !
i can understand the need for biopsy as the last step in diagnosis if nothing else works

I disagree, according to Conrad Fischer,(whom I quoted above), a bone biopsy should always be done (regardless of positive or negative blood culture), because it affects the management. You want to treat according to organism and its sensitivity (Which I talked about above).

As for the bone scan instead of MRI, for the feet and spine, I've never read that before, but I could see the logic.

 

[badgerred]

Regarding osteomyelitis in the foot, I thought the inital test to order is a 3 view X-ray? I thought you get MRI to confirm.

 

[Rendar5]

Some points on PE workups:

chest x-ray's in suspected PE patients are not used to look for evidence of a PE, they're used to look for other causes of SOB or CP.

V/Q and Spiral CT are roughly equivalent tests. Just realize that V/Q scan gives back low/medium/high probability scores, and that it's going to look weird in a couple other scenarios (I totally forget what, but possibly lobar pna, but this is not something that would show up on step II)

D-Dimer's are used to r/o PE only if there is a low probability of having a PE. Otherwise they're useless.

The short of it:
You can use Well's criteria for assessing probability of PE, and realize sinus tach gets you to low probability automatically. You go straight to V/Q or Spiral if the patient has a medium or high probability of having PE. Go to D-Dimer if low probability. If D-Dimer is negative, you're done. If it's positive you move onto the confirmatory tests. CXR has no role in the workup of PE, specifically; but it does have a role CP and SOB workups, which is why you will have to order it in these patients.


The other point I wanted to make on osteomyelitis, I disagree with Fisher that the best initial diagnostic test is an X-Ray. They have extremely low sensitivity because the findings are late in the course. In those tests that are positive, you could clinically diagnose it without the X-Ray most likely. In the real world, if your hospital's standards of care allow it, you probably should skip this and go toward a test with better sensitivity that's still cost-effective. BUT, for the purposes of the board, Fisher's answer would be the correct one.

 

[badgerred]

you probably should skip this and go toward a test with better sensitivity that's still cost-effective. BUT, for the purposes of the board, Fisher's answer would be the correct one.

What's a cost effective test that is more sensitive? Both CT and MRI are more expensive tests and are not really considered to be cost effective tests and ultrasound is not an option. Nearly every program I've been to orders the 3 view X-ray of the foot in patients suspected of osteomyelitis as the initial test of choice.

 

[superocker]

Some points on PE workups:

chest x-ray's in suspected PE patients are not used to look for evidence of a PE, they're used to look for other causes of SOB or CP.

V/Q and Spiral CT are roughly equivalent tests. Just realize that V/Q scan gives back low/medium/high probability scores, and that it's going to look weird in a couple other scenarios (I totally forget what, but possibly lobar pna, but this is not something that would show up on step II)

D-Dimer's are used to r/o PE only if there is a low probability of having a PE. Otherwise they're useless.

The short of it:
You can use Well's criteria for assessing probability of PE, and realize sinus tach gets you to low probability automatically. You go straight to V/Q or Spiral if the patient has a medium or high probability of having PE. Go to D-Dimer if low probability. If D-Dimer is negative, you're done. If it's positive you move onto the confirmatory tests. CXR has no role in the workup of PE, specifically; but it does have a role CP and SOB workups, which is why you will have to order it in these patients.


The other point I wanted to make on osteomyelitis, I disagree with Fisher that the best initial diagnostic test is an X-Ray. They have extremely low sensitivity because the findings are late in the course. In those tests that are positive, you could clinically diagnose it without the X-Ray most likely. In the real world, if your hospital's standards of care allow it, you probably should skip this and go toward a test with better sensitivity that's still cost-effective. BUT, for the purposes of the board, Fisher's answer would be the correct one.

I do agree on the PE work up
rule put with D Dimers
confirm with spiral CT ( vs VQ CTs are easier to read and faster .....havent ever seen a VQ being done ...so assuming they are slower...........)

Now Osteomyelitis

CXR should be the first test................anything do with the bone you normally do order an X ray

Negative order an MRI

Bone Scan -will not pick up soft tissue so well ..........so I would go with the MRI ANYWHERE on the body as kaplan says they have equal sensitivities

Bone Biopsy will always be the last measure reserved to confirm all negative tests !dont subject the dude to pain ....................

 

[Rendar5]

I do agree on the PE work up
rule put with D Dimers
confirm with spiral CT ( vs VQ CTs are easier to read and faster .....havent ever seen a VQ being done ...so assuming they are slower...........)

Now Osteomyelitis

CXR should be the first test................anything do with the bone you normally do order an X ray

Negative order an MRI

Bone Scan -will not pick up soft tissue so well ..........so I would go with the MRI ANYWHERE on the body as kaplan says they have equal sensitivities

Bone Biopsy will always be the last measure reserved to confirm all negative tests !dont subject the dude to pain ....................

Well, my point with real world osteo is that X-Ray's are going to miss something like 80+% of osteomyelitis because it takes several weeks for pathologic signs to appear on that test. It still seems like standard of care for some reason (like ppl being cautious about shellfish allergies and giving contrast despite no connection between the too) so ignore my rant for the purposes of the board.

 

[medInUSA]

what if you started the patient on antibiotics say for staph and he gets better
why would you want to subject the patient to pain (unless you are submitted to some masochistic desires of the patient)....
especially if cultures are positive !
i can understand the need for biopsy as the last step in diagnosis if nothing else works

Because the antibiotics you give is dependent on the organism that you find in the bone biopsy and culture and its sensitivity

For MSSA you give IV oxacilin or nafcillin

For MRSA you give IV vanco or linezolid or daptomycin

For GM negatives you Give ORAL quinolones.

If you were the patient wouldn't you want the peace of mind to know that you are being treated for the right organism. Additionally why would you want to get treated IV for staph while there is a possibility that you might have a gram negative organism you could be treated with oral antibiotics?

Because guess what??? IF after 4-6 weeks the ESR is still elevated, the next step is go in there with surgical debridement!!!!

 

[medInUSA]

I do agree on the PE work up
rule put with D Dimers
confirm with spiral CT ( vs VQ CTs are easier to read and faster .....havent ever seen a VQ being done ...so assuming they are slower...........)

Now Osteomyelitis

CXR should be the first test................anything do with the bone you normally do order an X ray

Negative order an MRI

Bone Scan -will not pick up soft tissue so well ..........so I would go with the MRI ANYWHERE on the body as kaplan says they have equal sensitivities

Bone Biopsy will always be the last measure reserved to confirm all negative tests !dont subject the dude to pain ....................

Again Your ideas about a bone biopsy and culture are completely wrong!!
The biopsy is NOT done to confirm the diagnosis of osteomyelitis. MRI is highly specific and sensitive for this purpose!!

The reason why we MUST do a bone biopsy is to determine the further management of the patient. You MUST do a bone biopsy to treat the osteomyelitis appropriately!! And this is the correct answer on the Test And in real life!!!

I have quoted my sources (Dr. Fisher step 3 book). If you insist on your statements please quote your reference or source!!!

 

[medInUSA]

Well, my point with real world osteo is that X-Ray's are going to miss something like 80+% of osteomyelitis because it takes several weeks for pathologic signs to appear on that test. It still seems like standard of care for some reason (like ppl being cautious about shellfish allergies and giving contrast despite no connection between the too) so ignore my rant for the purposes of the board.

Just as you dont skip the EKG and jump to the stress test
Just as you dont skip the Chest X-ray and jump to the Chest CT

you cannot skip the X-ray and jump to the MRI.

Furthermore, it is true that it takes several weeks for the periosteal elevation to appear on X-ray. But guess what?? The patient likely presents several weeks after the infection began, they don't rush to the doc right away.

 

[Rendar5]

Just as you dont skip the EKG and jump to the stress test
Just as you dont skip the Chest X-ray and jump to the Chest CT

you cannot skip the X-ray and jump to the MRI.

Furthermore, it is true that it takes several weeks for the periosteal elevation to appear on X-ray. But guess what?? The patient likely presents several weeks after the infection began, they don't rush to the doc right away.

Actually, a lot of times they skip the cervical spine X-Ray and jump straight to the CT scan of the cervical spine for clearing patients from C-Collars. I have to run but i can get into the reasons. Another example, you skip D-Dimers and go straight to imaging for medium probability and higher PE workups.

 

[medInUSA]

Please don't bother posting your reasons!! I really don't want to get into that discussion.

All I am saying for all the readers is that if you answer MRI before X ray you will get the answer wrong on the actual Test!!!

 

[Rendar5]

Please don't bother posting your reasons!! I really don't want to get into that discussion.

All I am saying for all the readers is that if you answer MRI before X ray you will get the answer wrong on the actual Test!!!

I thought I already posted that X-ray would be the right answer on a test, but not necessarily in the real world. Please don't tell me I'm wrong in real life if you're not even going to listen to my clinical reasoning. It's important to know both the test answer and where it may differ from real life.

The reason I probably would not use a test that has <20% sensitivity is that I'm going to need to go to the next test regardless of results, either as confirmation of a positive result, or because I don't believe my negative result (the exact same thing with the D-Dimer issue). The only exceptions would be clinically obvious osteomyelitis.

 

[medInUSA]

All right dude, chill out!, I'm just pointing out the standard of care at the current time.

From Harrison's

"A variety of radiologic tests are available for evaluation of osteomyelitis (Table 120-1). Evaluation usually begins with plain radiographs because of their ready availability, although they typically show no abnormalities during early infection. Three-phase bone scans (99Tc-monodiphosphonate) offer high sensitivity but are often of low specificity, especially in the presence of underlying bone abnormalities. There is a lack of consensus over the optimal use of other radionuclide studies, and there is considerable variation between institutions in their use. Use of MRI (Fig. 120-1) is expanding because of its high sensitivity and specificity as well as its ability to demonstrate associated soft tissue abnormalities, but this modality is not available at all institutions."

 

[pushinglass]

So for 2010 USMLE Step 3 answers for PE diagnosis, are they now up to date and Spiral CT (CTA) is done instead of V/Q scan unless contrast allergy or renal failure or is V/Q scan still the answer despite the PIOPED II trial?

 

[OveractiveBrain]

So for 2010 USMLE Step 3 answers for PE diagnosis, are they now up to date and Spiral CT (CTA) is done instead of V/Q scan unless contrast allergy or renal failure or is V/Q scan still the answer despite the PIOPED II trial?

The test is up to date.

Pick the CT scan unless contraindicated.