Abstract
We read with great interest the recent publication by Kim et al. (1). The use of Tc-99m-methoxy-isobutyl-isonitrile (MIBI) for differentiation of malignant thyroid nodules has been shown to be a very useful diagnostic tool. However, it is important for every diagnostic tool to be evaluated correctly, but unfortunately and without doubt, this meta-analysis (1) fails in its design and systematic review, reaching an erroneous conclusion.
The real diagnostic value of a MIBI thyroid scan is its potential usefulness in the evaluation of a thyroid nodule with a fine-needle aspiration biopsy (FNAB) classified as Bethesda I, III, IV, and V, and this must be understood correctly. The use of MIBI to assist in the diagnosis of thyroid nodules has been used for more than two decades, but its real value was suggested in 2004 when our group (2) reported that the absence of MIBI uptake (at any time after MIBI administration) in a hypofunctional (as determined by a Tc-99m functional thyroid scan) thyroid nodule of
Every study designed as a meta-analysis uses a statistical approach to combine the results from multiple studies in an effort to increase power (over individual studies). These multiple studies need to be comparable studies clearly containing all the information needed for such analysis and comparison. We believe that the recent meta-analysis published in Thyroid (1) fails as a meta-analysis due to the fact that of all the studies used to reach its conclusion, only three (2,4,5) have a comparable methodology and full description to evaluate the MIBI uptake in the thyroid nodule correctly and/or comparatively. The other studies used in the meta-analysis in question have varying characteristics that make them not comparable and therefore not usable to reach conclusions.
The studies by Beristain-Hernández et al., Demirel et al., and Erdil et al. do not use comparative images (functional and MIBI thyroid images; for references, see Kim et al.) (1). Boi et al. and Kresnik et al. describe that a negative MIBI was considered when uptake was present in one of the two time points. Wale et al. only used one time point. Alonso et al. established three (not two) different degrees of MIBI uptake. Campennì et al. evaluate a mathematical index between the MIBI uptake in the thyroid nodule and the adjacent thyroid gland. Leidig-Bruckner et al., Nakahara et al., and Onkendi et al. use tetrofosmin and thallium-201, not MIBI. Finally, in the studies by Onkendi et al., Sundram et al., and Yordanova et al., the methodology is not very clear.
From all of the above, it is clear that the meta-analysis by Kim et al. (1) includes publications with confusing and/or different techniques to obtain the information, acquire the images, and classify the findings. There is only one finding that continues to hold its ground: when a hypofunctional thyroid nodule does not show uptake of MIBI, the thyroid nodule is benign, which allows malignancy to be “ruled out” (NPV 100%). Thyroid nodules with a non-diagnostic FNAB report and a positive MIBI scan will need to undergo additional diagnostic testing or surgical intervention. A possible explanation as to why there is still confusion regarding this diagnostic test (1) is that several authors have tried to come up with grading systems, with different scores, mathematical models, and normal to abnormal tissue semi-quantitative indexes trying to improve specificity and the test's capacity to “rule in” malignancy, which certainly has not happened. Considering the epidemiology of an increasing incidence/detection of thyroid nodules, most of them of benign etiology, a diagnostic test that can actually “rule out” malignancy is of great help.