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Centre for Evidence-
Based Medicine

Completed Diagnosis Worksheet for Evidence-Based Physiotherapy Practice

Citation

Schiffman EL, Anderson GC, Fricton JR, Burton K, Schellhas KP. Diagnostic criteria for intrarticular temporomandibular disorders. Community Dent Oral Epidemiol 1989;17:252-257.

Are the results of this diagnostic study valid?

  1. Was there an independent, blind comparison with a reference ("gold") standard of diagnosis?
    A blind comparison was made. However, it is not clear if the reference test (arthrotomography) was performed independent of the clinical tests.

    The validity of the reference standard is not specified. No convincing evidence was provided in the article to support that this test is the best reference or gold standard. There is some evidence that MRI is the best reference standard.
  2. Was the diagnostic test evaluated in an appropriate spectrum of patients (like those in whom it would be used in practice)?
    A representative mix of cases appears to be present.
  3. Was the reference standard applied regardless of the diagnostic test result?
    Yes

Are the valid results of this diagnostic study important?

Your calculations

  • Study Setting: tertiary care
  • Target disorder: internal derangement
  • Reference standard: arthrotomography
  • Diagnostic test: diagnostic criteria for intraarticular TM disorder (Table 3 of the paper) included positive history of mandibular limitation, no reciprocal click, no coarse crepitus, maximum opening less than or equal to 35 mm, passive opening stretch less than 40 mm, contralateral movement less than 7 mm, no S-curve deviation and tomography findings of decreased translation of the ipsilateral condyle.
Internal Derangement of TMJ
Present Absent
Diagnostic Criteria
(Sample A)
Positive

42

a

2

b

a + b

Negative

7

c

8

d

c + d

Totals

a + c

50

b + d

10

a + b + c + d

Schiffman et al 1989
(Sample A)
Sensitivity* = a/(a+c) 0.86
Specificity* = d/(b+d) 0.80
Likelihood ratio for a positive test = LR+ = sens/(1-spec) 4.30
Likelihood Ratio for a negative test = LR- = (1-sens)/spec 0.18
Positive Predictive Value = a/(a+b) 0.96
Pre-test Probability (prevalence) = (a+c)/(a+b+c+d) 0.83 0.50 0.20
Pre-test odds = prevalence/(1-prevalence) 4.88 1.00 0.25
Post-test odds (+ test) = Pre-test odds x LR+ 20.99 4.3 1.08
Post-test odds (- test) = Pre-test odds x LR- 0.86 0.18 0.05
Post-test Probability (+ test)
= Post-test odds/(post-test odds +1)
0.95 0.81 0.52
Post-test Probability (- test)
= Post-test odds/(post-test odds +1)
0.46 0.15 0.05
* Sensitivity and specificity are reported in the text and the marginal total for a+c and b+d were reported in table 2. No further data were available to allow for extraction of the 2x2 table (cells a, b, c, d). The highlighted segments of the above table reflect the Schiffman et al 1989 sample A results. To assist the reader in applying these clinical findings, the additional calculations present calculations for a low (e.g. 0.20) and intermediate (e.g. 0.50) pre-test probability / prevalence.

Can you apply this valid, important evidence about a diagnostic test in caring for your patient?

  1. Is the diagnostic test available, affordable, accurate, and precise in your setting?
    Yes. History, clinical evaluation and tomography are commonly available, affordable, done accurately (the imaging protocol would need to be determined per site) and precisely in our community.
  2. Can you generate a clinically sensible estimate of your patient's pre-test probability (from practice data, from personal experience, from the report itself, or from clinical speculation)?
    This is dependent on the reader's data management system available in the practice setting. The prevalence in the study sample was 0.83.
  3. Will the resulting post-test probabilities affect your management and help your patient? (Could it move you across a test-treatment threshold?; Would your patient be a willing partner in carrying it out?)
    Yes. If the pretest probability is a toss-up (e.g. 0.50) the post-test probability for positive test results firms up to 81%. However, if the pretest probability is low (e.g. 0.20), neither a positive nor a negative test result brings the post-test probability into a range where intervention would likely change (0.05, 0.52 respectively). Similarly, for the high pretest probability (e.g. 0.83, as in Schiffman et al 1989) a negative test result does not exclude internal derangement (post-test probability = 0.46) and a positive result further confirms your previous strong clinical impression. The tests are of minimal risk to the patient and therefore one should be willing to carry them out.
  4. Would the consequences of the test help your patient?
    Marginally to definitely. Yes depending on the prevalence of ID in your practice setting. The treatment for internal derangement differs to some extent in physiotherapy management from other TMD. It would be more informative if the LR+ for each subgroup (for example: internal derangement with reduction and without reduction) were reported.

Additional Notes

  1. In Schiffman et al 1989, the assumption is made that there were no missing data. Table 4 notes that 10% of the normals of sample A and 27% with the disorder were not classifiable. This is contrary to table 2 where the sample number are noted to be as follows:
    target disorder present n = 50
    target disorder absent n = 10
  2. see also Schiffman E, Haley D. Sensitivity and specificity of diagnostic criteria for temporomandibular internal derangements. J Dent Res 1994;73(1 NSI):440.

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