¹²³I-MIBG Scintigraphy and ¹⁸F-FDG PET in Neuroblastoma

TO THE EDITOR: We read with great interest a recent article by Sharp et al. (1) in which the authors compared the diagnostic utility of ¹²³I-metaiodobenzylguanidine (MIBG) scintigraphy and ¹⁸F-FDG PET in neuroblastoma. In this retrospective study, a total of 113 paired ¹²³I-MIBG and ¹⁸F-FDG PET scans of 60 patients were compared.

The authors concluded that ¹⁸F-FDG PET was superior to ¹²³I-MIBG scanning in detecting stage 1 and 2 neuroblastoma. Only 10 patients, however, had stage 1 or 2 disease, and of these, 5 patients were undergoing imaging for diagnosis and 5 for follow-up, indicating nonuniform patient groups with different clinical questions. Because the methods of statistical analysis were not described in the article, it was difficult to comprehend the results of the confidence intervals. The calculation of confidence intervals usually requires the assumption that the distribution of the sample population is normal; however, given the small sample size of the studied groups with stage 1 and 2, a normal distribution could not be expected. Thus, the conclusion that ¹⁸F-FDG PET is superior for depicting stage 1 and 2 neuroblastoma is doubtful. We would appreciate information about the authors' methods of statistical analysis and their comments on the results for stage 1 and 2 neuroblastoma in regard to the statistical power of the tests.

The authors further concluded that ¹²³I-MIBG scanning was superior to ¹⁸F-FDG PET in the evaluation of stage 4 neuroblastoma, “especially during initial chemotherapy, primarily because of the better detection of bone or marrow metastases.” In contrast to these findings, Kushner et al. (2) reported a study of 51 patients with high-risk neuroblastoma in which ¹⁸F-FDG PET was equal or superior to ¹²³I-MIBG scanning for “identifying neuroblastoma in soft tissue and extra-cranial skeletal structures, for revealing small lesions, and for delineating the extent and localizing sites of disease.” Sharp et al. (1) mentioned and discussed the findings of Kushner et al. briefly and from another angle; for example, that Kushner et al. “primarily addressed appropriate follow-up for patients with progressive disease after primary tumor resection in the absence of cranial vault lesions.” The authors, however, did not discuss the discrepancy of the results between the 2 studies. We would appreciate a discussion by the authors in this regard.

The authors described ¹²³I-MIBG as being inferior to ¹⁸F-FDG PET in stage 1 and 2 neuroblastoma and superior to ¹⁸F-FDG PET in stage 4 neuroblastoma, based on the numbers of scans and patients for which either of the 2 modalities detected more lesions. The authors, however, did not discuss whether the better performance of either modality resulted in a change in clinical stage or clinical management. We would appreciate information from the authors on this subject.