TO THE EDITOR
Technetium-99m Bone Scintigraphy in the Detection of Cervical Spine Metastases in Oncological Patients; Methodological Issues on Diagnostic Value
I was interested to read the paper by Park SM and colleagues published in the Nov 2017 of Spine.1 Diagnostic value of bone scan in detecting bone metastases limited to the cervical spine in oncological patients remains uncertain. The purpose of the authors was to assess the diagnostic accuracy of bone scintigraphy (BS) in the above-mentioned patients. The BS findings of the patients, evaluated by nuclear medicine physicians, were assessed with respect to their usefulness for detecting cervical spine metastases. Magnetic resonance imaging findings, evaluated by radiologists, were used as the reference standards. Based on their results, the sensitivity of BS in the detection of cervical spine metastases was 59.1%, with a 40.9% rate of false-negative diagnoses; the specificity was 94.6%, with a 5.4% rate of false-positive diagnoses.1
However, it is crucial to know that diagnostic value can be considered diagnostic accuracy (validity) and diagnostic precision (reliability). To assess validity, for qualitative variables, sensitivity, specificity, positive predictive value, negative predictive value, likelihood ratio positive and likelihood ratio negative as well as diagnostic accuracy and odds ratio (ratio of true to false results) are among the most appropriate tests.2 Reliability (precision) as different methodological issue of diagnostic value should be assessed using appropriate tests. For qualitative variables, weighted kappa should be applied.2–6 Moreover, considering the specificity of BS equal to 94.6% as well as diagnostic odds ratio equal to 25, it is not fair to conclude that BS cannot accurately diagnose metastases in the cervical spine in oncological patients. Such a sweeping conclusion should be supported by the above-mentioned statistical and methodological issue. It means, sensitivity alone is not a good estimate to judge about diagnostic value of a test. Therefore, I would conclude that BS is not a proper screening tool to detect bone metastases limited to the cervical spine in oncological patients. To make it simple, considering high specificity and diagnostic OR equal to 25 (ratio of true to false results), diagnostic accuracy of BS can be acceptable.