Osteomyelitis... next step in management? Xray or Bone Scan?

[ej37]

So... uptodate says next best step in management when osteo is suspected is Xray. Then do either bone scan or MRI. Obviously acute osteomyelitis won't show up on Xray until at least a week afterwords, but my understanding is xray is to r/o chronic osteo or other pathology with a cost-effective 1st test.

Kaplan lecture notes also confirm this, they say "best" test to confirm osteo (highest specificity) is bone scan or MRI (doubt we would be offered both choices).

But now I'm super confused, on my medicine shelf exam there was a question asking for "next best step" in suspected osteo and xray wasn't even an option. I'm 100% sure it said "next step in management" and not best test overall... I went with bone scan, not really liking my choice. Now today I see a Kaplan question (Step 2 CK Qbook 5e Peds test #1 question 43 on page 339) that is literally almost word-for-word the same question I had on my shelf exam. Although they DO give xray as a potential answer choice... but say its wrong??!?!

Anyone have any ideas or seen this on their actual step 2/3?

At this rate, I think I'm still putting Xray as my "best initial test" but can't understand the Kaplan Qbook question.

---

Members don't see this ad.

 

[Valadi]

Why would you pick a less sensitive test as a diagnostic tool when MRI (most places do this over bone scan now) is more sensitive and specific.

 

[Valadi]

Oh sorry forgot to answer 2nd part. I have seen this question pop up on my shelf exams, step 2, practice questions, and grand rounds presentations over and over.

MRI is generally the right answer. X-ray would only be correct in very specific circumstances.

 

[sylvanthus]

MRI is the best test overall and most accurate. But, I believe xray is the best "initial" test. Yes it is less specific and sensitive, but we don't always jump to the most accurate right off the bat. MRI is more expensive, takes longer, etc etc. So, i believe xray is done first unless the question specifically asks for the "best" or "most accurate."

 

[dangit]

isn't Bx and Cx the best test/most accurate?

so here's what i'm thinking:

best initial test: X-ray

if questions says "next best step in management" and if pt had infection for less than 2 weeks, then go with MRI

most accurate test: Bx, Cx

what do you guys think?

 

[sylvanthus]

Ahh yes forgot about biopsy, ya gotta toss that into the mix also.

 

[Valadi]

I 100% agree that for certain patients plain radiographs are a cost effective first option.

However, I think the USMLE/NBME is testing if you understand when to order a test with high-specificity and negative predictive value.

In the case of osteomyelitis, if we had unlimited funds (you are not in a fee-for-service or HMO for the USMLE) MRI is the best initial step because it has the highest likelihood of detecting the disease (90% sensitivity). In addition it has a very high specificity (80-90%), and a high negative predictive value for ruling out the disease.

In contrast, xray imaging has a sensitivity as low as 14%, poor specificity (around 50%), and a poor negative predictive value ratio. So if it's negative it tells you nothing. Plain films are good, however, for ruling out other things that might be going on in the area, if your differential is broad.

For the majority (not all) questions you get about osteo, MRI will be the best initial step in management. If it's vertebral osteo you always get MRI if there is neurological compression.

In terms of osteo follow-up, however, plain films are used, not MRI.

And yes, bx/cx is the gold standard

 

[MossPoh]

Usually, best initial test is radiograph.
If that is negative, it is MRI unless contraindicated (Pacemaker or the like), in which case you do the bone scan. (Basically, bone scan is rarely the right answer unless they want to be jerks and put nothing)

Bone biopsy is a critical step, but it is critical for determination of treatment. You don't really get a picture of the severity of the problem.

Sometimes, they will have "probing the wound" or somethign similar on there, which would be first if on the choices and it is next step in management. You may have your assumption it is osteomyeltis, but it is usually good to see the depth of the wound.

It is really hard to answer these questions because we tend to forget or never see an important detail in the stem that gives away what it should be.

 

[OveractiveBrain]

How do I diagnose Osteo?

Check out this guy... he explains it pretty well.
onlinemeded.org Minute 12:30
Here's the gist:

1st Test = Xray, (if osteo skip to biopsy)

​

then = bone scan (do not perform if cellulitis, test of choice if xray negative and no cellulitis)

​

then = MRI (perform if Xray negative and cellulitis is present)

​

Best = Biopsy (and only once, just to find the bugs, you use clinical picture to track course)

Treatment = Surgical Debridement, Culture, and tailored antibiotics.

 

[AndyRSC]

That site looks ****ing awesome, Overactive, thanks! Since I tend to think algorithmically, it's exactly what I needed.

 

[hot sauce]

I 100% agree that for certain patients plain radiographs are a cost effective first option.

In the case of osteomyelitis, if we had unlimited funds (you are not in a fee-for-service or HMO for the USMLE)

Part of USMLE is to choice appropriate management including considerations such as cost effectiveness. Choose what is recommended in real life. Now if I was suspicious of osteo in a patient I would probably get an MR, but it would depend on the details of the presentation (and I don't know if that is correct). I would just caution against the mentality of money is not an issue when taking the exam (which may not have been what you were meaning to suggest but was what it sounded like to me).