Presentation is loading. Please wait.

Presentation is loading. Please wait.

Diagnostic Tests for Lower Extremity Osteomyelitis Laura Zakowski, MD* *no financial disclosures.

Similar presentations


Presentation on theme: "Diagnostic Tests for Lower Extremity Osteomyelitis Laura Zakowski, MD* *no financial disclosures."— Presentation transcript:

1 Diagnostic Tests for Lower Extremity Osteomyelitis Laura Zakowski, MD* *no financial disclosures

2 Objectives n List typical findings for LE osteomyelitis n Describe use of likelihood ratios in diagnostic test results n Review a study of osteomyelitis diagnostic test results n Quickly and easily determine post test probabilities from likelihood ratios

3 Case #1:Patient with a foot ulcer n A 52 year old woman comes to clinic with a foot ulcer u Diabetes type 1 for 40 years u Complications u 1 week of erythema, pain and swelling

4 Case #1:Patient with a foot ulcer n Physical exam: u 130/84, 90, 36.1 u Diminished pedal pulses u 2.2 x 1.5 cm ulcer in the toe web u Probes to bone n Laboratory: u WBC 9500, ESR 75, gram stain GPC, GNR n Xray: soft tissue swelling and erosion

5 Case #1:Patient with a foot ulcer n A. How likely is osteomyelitis? n B. How sure do we want to be of the diagnosis before treating? n C. If we want to discard the diagnosis of osteomyelitis, how low on the scale should we be?

6 Case #2:Patient with a foot ulcer n A 64 year old man with a non-healing ulcer u Present for 3 weeks, treated with a course of antibiotics (10 days amox/clav) u Not painful u Type 2 diabetes with complications u No history of foot ulcers

7 Case #2:Patient with a foot ulcer n Physical exam u BP 130/80, P 70, T 37.0 u Decreased pulses and sensation u 1 cm diameter, no probe to bone n Laboratory u WBC 14, 500 ESR 25 n Xray: no abnormalities

8

9 Case #2:Patient with a foot ulcer n How likely is osteomyelitis?

10 Diabetic foot ulcers n 85% diabetes-related amputations preceded by foot ulcers n Risk factors: u Neuropathy u Hyperglycemia u PAD n Trauma often inciting factor n Retrospective cohort: 15% patients with ulcer develop osteomyelitis

11 Diabetic foot ulcers n History n Physical exam maneuvers u Ulcer size u Probe-to-bone test F Sterile, blunt stainless steel probe F No soft tissue between probe and bone

12 Diabetic Foot Ulcers n Wagner Grade u 0: no open lesions u 1: superficial ulcer u 2: deep ulcer to tendon, bone, joint u 3: deep ulcer with abscess, osteomyelitis or tendonitis u 4: localized gangrene u 5: gangrene of foot

13 How can we determine presence of osteomyelitis? PROBABILITY OF DIAGNOSIS 0%?? Test rules out osteo Not sure of diagnosis Test confirms osteo 100%

14

15 Diagnostic test evidence for osteomyelitis n Search for diagnostic test studies u 21 out of 279 met criteria u Reference standard n No studies of history n Seven studies of physical exam u N = 509 patients JAMA 2008;299:806-13

16 Likelihood ratio n Converts pretest probability into posttest probability n Derived from sensitivity and specificity n Indicates the accuracy of the test  accuracy =  likelihood  accuracy =  likelihood Test result with disease Test result without disease

17 Positive likelihood ratio n If you have a positive test result: sensitivity (patients who do have the disease with a positive test result)__ 1-specificity (patients who do not have the disease with a positive test result)

18 Positive Likelihood Ratio Test result Diagnosis/Disorder (+) (-) (-) (+) Sensitivity = a/a+c = 99/99+1 = 0.99 Specificity = d/b+d= 98/98+2 = 0.98 Sensitivity 1-specificity LR (+) = 0.99/ = 49.5 LR=

19

20 Negative likelihood ratio n If you have a negative test result: 1 - sensitivity (patients who do have the disease with a negative test result)___ specificity (patients who don’t have the disease with a negative test result)

21 Negative Likelihood Ratio Test result Diagnosis/Disorder (+) (-) (-) (+) Sensitivity = a/a+c = 99/99+1 = 0.99 Specificity = d/b+d= 98/98+2 = sensitivity specificity LR (-) = /0.98 = 0.01 LR(-)=

22

23 Sensitivity, specificity and likelihood ratios SensSpecLR(+)LR(-) 95%95% %70% %95% %70%

24

25

26

27

28 Likelihood ratio short cuts LR % change (increase) LR Or:1/21/51/10 % change (decrease)

29 Will the results change your management? POST TEST PROBABILITY Don’t test or treat Test, then treat based on results Don’t test, TREAT!

30 Physical exam maneuvers Finding LR + LR - Probe to bone Ulcer area >2 cm Ulcer inflammation

31 Laboratory findings Test LR + LR - ESR > Swab culture 11 Plain films MRI

32 Size OR probe to bone Inflammation

33 swab xray ESR

34 MRI- MRI+

35 IDSA guidelines (2004) n If not sure of osteo: u Plain radiograph u Treat for two weeks u Repeat plain radiograph u If suspicious findings, evaluate for osteomyelitis u Bone biopsy is the gold standard


Download ppt "Diagnostic Tests for Lower Extremity Osteomyelitis Laura Zakowski, MD* *no financial disclosures."

Similar presentations


Ads by Google