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Letters to the Editor |
Departments of Endocrinology (K.M.v.T., R.P.F.D., T.P.L.) and Nucleair Medicine (P.L.J.) University Hospital Groningen 9700 RB Groningen, The Netherlands
Recently, Wang et al. (1 ) reported on the usefulness of 18F-fluoro-2-deoxy-D-glucose (FDG)-positron emission tomography (PET) for localizing residual differentiated thyroid carcinoma in a group of 37 patients with a negative low-dose 131I whole body scan (DxWBS). They report that FDG-PET was positive in 14 of 20 patients who were considered to have residual disease, yielding a sensitivity of 71%, in agreement with other reports (2 3 4 ). In 19 of the 37 patients, performing FDG-PET resulted in a change in clinical management, which included a high-dose 131I in 13 patients. They correctly point out that some authors perform a high-dose 131I posttreatment WBS (RxWBS) in case of suspicion of residual thyroid cancer despite a negative DxWBS (5 6 ). The impact of FDG-PET scanning on the clinical management may, thus, depend on the diagnostic and therapeutic 131I WBS protocol used. For this reason, the diagnostic yield of FDG-PET in negative RxWBSs cannot be easily deduced from the data provided by Wang et al. (1 ).
We have performed FDG-PET in a consecutive series of 11 patients
with differentiated thyroid carcinoma who all had undergone total
thyroidectomy and 131I-ablation therapy and in
whom serum thyroglobulin (Tg), measured with a commercial available RIA
(CIS Bio International, Gif-sur-Yvette, France) during
suppression therapy with T4, remained detectable
(>1.5 ng/mL), despite a negative RxWBS with 150 mCurie
131I. Patient characteristics of this group are
listed in Table 1
. When FDG-PET (using an
ECAT 951/31 camera; Siemens/CTI, Knoxville, TN) was performed,
the median age was 60 yr (range, 26–75) and the median cumulative dose
of 131I was 500 mCurie (range, 50–800). Median
Tg levels during FDG-PET was 9.7 ng/mL (range, 3.4–149). In all
patients FDG-PET was positive.
|
, abnormal FDG-PET uptake was found mostly in
cervical nodes (eight times) and intrathoracically (six times).
Findings of other imaging procedures, including computed tomography
scan, magnetic resonance imaging, and x-ray imaging, were concordant in
two patients (cases 1 and 2), partly concordant in another two patients
(cases 3 and 4), and discordant in the other seven patients, with
negative imaging procedures in six of them (cases 6–11). Three
patients underwent surgery to obtain histologic verification of the
suspected metastatic lesion. One patient (case 1) showed a metastatic
lesion in the pelvis, which was treated successfully with radiotherapy.
Three years later, this patient has presented with multiple lung
metastases. In two patients (cases 6 and 7) cervical lymphadenectomy
was performed, but no metastatic tumor was found. We decided not to
perform extensive surgery only for verification of the FDG-PET results
in the presence of suspected lung metastases or intrathoracic
involvement (cases 2, 3, 4, 8, and 9). Surgery was also not performed
in two patients who only showed FDG-PET uptake in cervical nodes,
because of serious cardiopulmonary disease in case 10 and because of a
sustained undetectable Tg level shortly after performing FDG-PET in
case 11. In these 10 cases none of the lesions found with FDG-PET
became clinically apparent after a median follow-up of 32 months
(range, 17–33), although the serum Tg level have increased in 8 cases
during suppression therapy with T4. Our preliminary experience with FDG-PET in Tg-positive and RxWBS-negative differentiated thyroid carcinoma patients thus suggests that FDG-PET frequently yields false positive results compared with other imaging techniques (7 of 11 cases, 64%) and that a meaningful change in clinical management directed by FDG-PET may be as low as 9% (1 of 11 patients).
Footnotes
Address correspondence: Michael S. Vaphiades, D.O., Harvey & Bernice Jones Eye Institute, Department of Ophthalmology, University of Arkansas for Medical Sciences, 4301 West Markham, Mail Slot 523, Little Rock, Arkansas 72205-7199.
Address correspondence to: K. M. van Tol, Department of Endocrinology, University Hospital Groningen, P.O. Box 30.001, 9700 RB Groningen, The Netherlands.
References
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