Reply: Scintigraphic TNM Staging of Tumors: A Proposition

REPLY: We read with interest the letter by Regi Oommen about potential changes in postoperative pathologic TNM (pTNM) staging brought about by integrating ¹³¹I whole-body scintigraphy (WBS) with ¹³¹I SPECT/CT in patients with differentiated thyroid cancer (DTC). In particular, the author has illustrated a DTC case in which preablative ¹³¹I WBS and ¹³¹I SPECT/CT changed the pTNM stage from T1N1bMx to T1N1bM1 when scintigraphy showed distant lung metastases that had been missed on chest radiography. SPECT/CT confirmed the lung uptake.

Among the patients enrolled in our study (1), 9 underwent preablative ¹³¹I WBS and ¹³¹I SPECT/CT. SPECT/CT was concordant with WBS in 7 of 9 patients, confirming residual tissues seen on planar scanning. In the remaining 2 patients, SPECT/CT was more accurate than WBS: in one patient, SPECT/CT identified a higher number of residues; in the other, SPECT/CT detected mediastinal lymph nodes and lung metastases occult on planar scanning, as well as a higher number of bone metastases (some of which were small and in the ribs). Moreover, SPECT/CT was more accurate than WBS in several of our patients studied with diagnostic radioiodine during long-term follow-up after radioiodine ablation, identifying occult locoregional or distant lesions not evident on planar scanning and contributing to selection of the most appropriate radioiodine therapeutic dose or to a change in therapeutic approach in some cases.

Schmidt et al (2) demonstrated that SPECT/CT determines lymph node involvement at the radioablation study more accurately than does planar imaging, altering management in roughly one quarter of DTC patients by upstaging or downstaging their disease.

On the basis of the above results, we conclude, in agreement with Dr. Oommen, that in patients scheduled for preablation diagnostic ¹³¹I scanning, integration of WBS with SPECT/CT is of extreme importance because of the resulting increase in specificity and sensitivity. In particular, this new procedure has the potential to modify pTNM stage by identifying locoregional iodine-avid lymph node metastases that need to be treated surgically before radioiodine ablation, as well as by detecting distant metastases and thus guiding one to the most appropriate radioiodine therapeutic dose or to a treatment alternative to radioiodine.

A reassessment of the role of ¹³¹I-WBS in the management of DTC patients is probably necessary in light of the high performance obtainable when ¹³¹I-WBS is integrated with SPECT/CT.