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Fair Performance of CT in Diagnosing Unilateral Vocal Fold Paralysis

Fair Performance of CT in Diagnosing Unilateral Vocal Fold Paralysis LETTERS Fair Performance of CT in Diagnosing Unilateral Vocal Fold Paralysis ashir et al reported the diagnostic performance of CT signs Bof unilateral vocal fold paralysis as evaluated by blinded radi- ologists. They highlighted the 2 best signs combined, medializa- tion of the posterior vocal fold margin and laryngeal ventricle dilation, as having a positive predictive value of 87%, specificity of 74%, and interrater reliability of k ¼ 0.50–0.54. The authors con- cluded that these CT signs should raise concern for ipsilateral vocal fold paralysis. However, important limitations apply. The first limitation pertains to the study design. In this retro- spective, case-control study, only patients who underwent laryn- goscopy by an otolaryngologist were included, while patients were excluded if they had a history of cancer, trauma, radiation, or surgery involving the larynx or pharynx. Spectrum bias arises when the study sample differs in case mix from that encountered in the clinical setting where these signs are intended to be used. Patients who undergo laryngoscopy may have more advanced disease, such as obvious dysphonia, resulting in overestimation of sensitivity. Excluding controls likely to have anatomic distortions FIGURE. Conditional probability for the diagnosis of unilateral vocal for other reasons results in overestimation of specificity. This fold paralysis based on CT. Predictive values (blue/solid lines, positive study may not generalize to many common scenarios for neck predictive value; red/dashed lines, negativepredictivevalue) with CT, such as surveillance for head and neck cancer or trauma. 95% confidence intervals (thin lines) were calculated from the sample The second limitation pertains to the results interpretation. sizes and estimated sensitivity and specificity of the 2-sign model in Predictive values depend on the underlying disease prevalence Bashir et al, using a standard logit method (MedCalc, Version 20.109; MedCalc Software). (Figure), especially when the inherent test characteristics are overall fair as in this case (sensitivity 62%, specificity 74%). Case- control studies typically do not reflect the prevalence of disease in Disclosure forms provided by the authors are available with the full text and PDF of this article at www.ajnr.org. the relevant clinical population, rendering predictive values mis- 2,3 leading. The positive predictive values in this study are inflated from those expected in real clinical practice because the preva- REFERENCES lence of unilateral vocal fold paralysis was 73%. If the prevalence 1. Bashir MH, Joyce C, Bolduan A, et al. Revisiting CT signs of unilateral is 10%, which is still likely an overestimate on typical neck CTs in vocal fold paralysis: a single, blinded study. AJNR Am J Neuroradiol 2022;43:592–96 CrossRef Medline my opinion, the positive predictive value of these CT signs would 2. Pavlou A, Kurtz RM, Song JW. Diagnostic accuracy studies in radiol- only be 21%. ogy: how to recognize and address potential sources of bias. Radiol I agree with the authors’ conclusion that “care must be taken Res Pract 2021;2021:e5801662 CrossRef Medline to translate suspicious findings appropriately.” Clinicians should 3. Deng F. Reporting predictive values for diagnostic tests. AJR Am J consider the patient’s risk factors and pretest probability of vocal Roentgenol 2018;211:W278 CrossRef Medline fold paralysis, as well as the fair diagnostic performance and reli- F. Deng ability of these CT signs, demonstrated in this study within the The Russell H. Morgan Department of Radiology and limitations of its design. Radiological Science Johns Hopkins University School of Medicine http://dx.doi.org/10.3174/ajnr.A7593 Baltimore, Maryland E64 Letters Dec 2022 www.ajnr.org http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png American Journal of Neuroradiology American Journal of Neuroradiology

Fair Performance of CT in Diagnosing Unilateral Vocal Fold Paralysis

Deng, F.
American Journal of Neuroradiology , Volume 43 (12): 1 – Dec 1, 2022
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American Journal of Neuroradiology
Copyright
© 2022 by American Journal of Neuroradiology
ISSN
0195-6108
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1936-959X
DOI
10.3174/ajnr.a7593
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Abstract

LETTERS Fair Performance of CT in Diagnosing Unilateral Vocal Fold Paralysis ashir et al reported the diagnostic performance of CT signs Bof unilateral vocal fold paralysis as evaluated by blinded radi- ologists. They highlighted the 2 best signs combined, medializa- tion of the posterior vocal fold margin and laryngeal ventricle dilation, as having a positive predictive value of 87%, specificity of 74%, and interrater reliability of k ¼ 0.50–0.54. The authors con- cluded that these CT signs should raise concern for ipsilateral vocal fold paralysis. However, important limitations apply. The first limitation pertains to the study design. In this retro- spective, case-control study, only patients who underwent laryn- goscopy by an otolaryngologist were included, while patients were excluded if they had a history of cancer, trauma, radiation, or surgery involving the larynx or pharynx. Spectrum bias arises when the study sample differs in case mix from that encountered in the clinical setting where these signs are intended to be used. Patients who undergo laryngoscopy may have more advanced disease, such as obvious dysphonia, resulting in overestimation of sensitivity. Excluding controls likely to have anatomic distortions FIGURE. Conditional probability for the diagnosis of unilateral vocal for other reasons results in overestimation of specificity. This fold paralysis based on CT. Predictive values (blue/solid lines, positive study may not generalize to many common scenarios for neck predictive value; red/dashed lines, negativepredictivevalue) with CT, such as surveillance for head and neck cancer or trauma. 95% confidence intervals (thin lines) were calculated from the sample The second limitation pertains to the results interpretation. sizes and estimated sensitivity and specificity of the 2-sign model in Predictive values depend on the underlying disease prevalence Bashir et al, using a standard logit method (MedCalc, Version 20.109; MedCalc Software). (Figure), especially when the inherent test characteristics are overall fair as in this case (sensitivity 62%, specificity 74%). Case- control studies typically do not reflect the prevalence of disease in Disclosure forms provided by the authors are available with the full text and PDF of this article at www.ajnr.org. the relevant clinical population, rendering predictive values mis- 2,3 leading. The positive predictive values in this study are inflated from those expected in real clinical practice because the preva- REFERENCES lence of unilateral vocal fold paralysis was 73%. If the prevalence 1. Bashir MH, Joyce C, Bolduan A, et al. Revisiting CT signs of unilateral is 10%, which is still likely an overestimate on typical neck CTs in vocal fold paralysis: a single, blinded study. AJNR Am J Neuroradiol 2022;43:592–96 CrossRef Medline my opinion, the positive predictive value of these CT signs would 2. Pavlou A, Kurtz RM, Song JW. Diagnostic accuracy studies in radiol- only be 21%. ogy: how to recognize and address potential sources of bias. Radiol I agree with the authors’ conclusion that “care must be taken Res Pract 2021;2021:e5801662 CrossRef Medline to translate suspicious findings appropriately.” Clinicians should 3. Deng F. Reporting predictive values for diagnostic tests. AJR Am J consider the patient’s risk factors and pretest probability of vocal Roentgenol 2018;211:W278 CrossRef Medline fold paralysis, as well as the fair diagnostic performance and reli- F. Deng ability of these CT signs, demonstrated in this study within the The Russell H. Morgan Department of Radiology and limitations of its design. Radiological Science Johns Hopkins University School of Medicine http://dx.doi.org/10.3174/ajnr.A7593 Baltimore, Maryland E64 Letters Dec 2022 www.ajnr.org

Journal

American Journal of Neuroradiology – American Journal of Neuroradiology

Published: Dec 1, 2022

References

  • Revisiting CT signs of unilateral vocal fold paralysis: a single, blinded study
    MH. Bashir; C. Joyce; A. Bolduan
  • Diagnostic accuracy studies in radiology: how to recognize and address potential sources of bias
    A. Pavlou; RM. Kurtz; JW. Song
  • Reporting predictive values for diagnostic tests