Osteomyelitis

[Chrismander]

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Can plain films rule out osteo, or only rule in? I thought I remember hearing a peds radiologist telling us that plain films are dumb studies to get if you're really thinking osteo, because a negative result doesn't mean anything. I only ask because my intern and resident on surgery were whining that the radiologist didn't give a firmer reading on a plain film of a toe of a diabetic patient with a suspected abscess. He wrote in the report that there weren't any signs of osteo, but he couldn't rule it out without an MRI and suggested clinical correlation yadda yadda yadda.

 

[Whisker Barrel Cortex]

Plain film is not a good modality to rule out osteomyelitis. It is actually the first study of choice for a couple of reasons. It can show obvious erosions is one. The second is that it shows the anatomy of the foot to better advantage. Especially in diabetic feet, chronic changes of the foot can make the anatomy on MRI difficult, so, at our hospital, we actually require a recent x-ray prior to MRI.

That being said. MRI is much much more sensitive and specific for osteomyelitis, even in the light of normal x-rays. In fact, even if the x-rays show osteo, MRI should be obtained to delineate the extent of involvement, especially if amputation is considered.

I geuss I assumed that this should be common knowledge among clinical collegues, but I geuss you intern and resident are not aware of this..

 

[ljl1982]

unable to attach file (exceeds SDN size limit)

MR Imaging of Osteomyelitis and Neuropathic Osteoarthropathy
in the Feet of Diabetics. Claude D. Marcus, MD et.al

 

[bosky]

I was told (by my medicine attending) that plain XR only shows osteomyelitis after 50% of the bone is destroyed. Not very sensitive.

 

[Carb Addict]

MRI does have its limitations, too, in that low marrow signal may simply indicate edema or hyperemia without infection. Need to have cortical disruption, bony abscess, or a sinus tract to definitely diagnose osteo with MRI.

Erdman W, Tamburro F, Jayson H, et al. Osteomyelitis: characteristics and pitfalls of diagnosis with MR imaging. Radiology 1991;180:533-539. Cited in Brant and Helms, 3rd ed, 1224.

 

[colbgw02]

you may want to try a bone scan. it's not as good as MRI (i don't think), but it can show you the entire skeleton and, depending on how many magnets you have, you can often get them done quicker than an MRI.

 

[Docxter]

I only ask because my intern and resident on surgery were whining that the radiologist didn't give a firmer reading on a plain film of a toe of a diabetic patient with a suspected abscess. He wrote in the report that there weren't any signs of osteo, but he couldn't rule it out without an MRI and suggested clinical correlation yadda yadda yadda.

Then your intern and resident are pretty uninformed (to be nice and not call them ...). Nothing short of a biopsy will tell you for certain if there is osteomyelitis (and even then sometimes chronic osteomyelitis with bone healing can sometimes be confused with osteosarcoma on light microscopy - not often, but I've seen it happen). Imaging studies have a certain sensitivity and specificity for osteomyelitis (and for most other indications for that matter), plain film, CT, MRI, bone scan, or Indium WBC scan. None are perfect, the sensitivity/specificity of each test has to be considered in the context of pretest probability, severity of disease, importance of test in changing management, and cost of test.

Here's the radiology report translation, which by the way makes a lot of sense to me:

1. Plain film is very low in sensitivity for diagnosis of osteomyelitis: Translated into common jargon, e.g. for your intern and resident, CANNOT RULE OUT OSTEOMYELITIS.

2. So point 2 in the radiology report, get a test with a higher sensitivity to rule out the disease, TRANSLATION: get an MRI.

3. And point 3 in the radiology report, increase your pretest probability (or test combination cumulative probabilities) when dealing with suboptimally sensitive/specific tests for a certain indication, TRANSLATION: correlate clinically, and with WBC, fever, ESR, prior outside films, yadda, yadda, yadda.

I don't see why your seniors are disappointed. They get a lousy test, and someone tells them the lousy test doesn't give the answer. What were they thinking (or were they thinking)?!!?!?

 

[f_w]

Diabetic rotting toes are a black hole for imaging. Different tests are useful at different points in the process, none is perfect.

-- Your rocket scientist seniors where looking for an abscess, if that is the case either an MRI or (for patients with a smaller wallet), a soft-tissue ultrasound would be the way to go.

-- MRI has plenty of false positives with bone edema from adjacent soft-tissue infection. The problem is that the toe will often come off in that setting because nobody has the patience to wait on it for a while (and see whether definitive osteomyelitis develops on plainfilm).

-- Another test which is quite sensitive but has its share of failures (FP/FN) in diabetic rotting toes is the 3-phase bone scan.

-- The plainfilm is actually quite useful if the infection is in place for a week or two. If the diabetic toe is still rotting after 2 weeks and the plainfilm is still negative, the negative predictive value for bone involvement is pretty good (and so is the PPV if you see clear evidence of osteo).

 

[Whisker Barrel Cortex]

-- MRI has plenty of false positives with bone edema from adjacent soft-tissue infection. The problem is that the toe will often come off in that setting because nobody has the patience to wait on it for a while (and see whether definitive osteomyelitis develops on plainfilm).

-- The plainfilm is actually quite useful if the infection is in place for a week or two. If the diabetic toe is still rotting after 2 weeks and the plainfilm is still negative, the negative predictive value for bone involvement is pretty good (and so is the PPV if you see clear evidence of osteo).[/QUOTE]

f_w,

That is quite different from what I've been taught. I'm going to look around myself, but do you have a certain article or study that you're getting this information from. Specifically, the plain film part.

 

[f_w]

The problem is that except for the orthopods, nobody is out to proove the value of plainfilms. Every study you look at will tell you 'xyz scan is better than plain-film or zyx scan is better than plainfilm'. I am talking about the actual clinical scenario, not the setting of studies designed to 'proove' the superiority of a technique over the other.

During residency, we had an orthopod who did nothing but osteomyelitis (often salvage). At the time one of the other residents reviewed the literature. If you dig through all of it, you will find that all techniques suck in one way or another and that only by putting all the pieces together, you will be able to do the right thing for the patient.

And in my practice (experience) that is:

- Plain-films. If they don't show it, you still have the film as a baseline allowing you to look for look for subtle changes later in the process (diabetics rarely have normal feet to start with).

- bone scan to r/o osteomyelitis (if its negative, you probably don't have osteo).

- MRI to assess for extent of involvement, presence of abscess, septic joings and other pre-surgical planning decisions.


Outside of teaching hospitals where you have tons of ortho and vascular surgery residents itching to operate (and trying to keep that patient from falling into their successors OR list), osteomyelitis is rarely a rapidly progressing life threatening disease that requires instant answers. Also, you will bump into less inflated egos on the surgical side which makes work so much easier.

 

[Direct Laryngoscopy]

MS2 here

How specific would be nuclear med be for ruling in/out osteo. We had a radiology lecture explaining the concept behind it and it seems like a great tool for showing an inflammatory process in progress.