Endocrine Abstracts

Introduction: Recurrences of differenciated thyroid carcinoma are occasionally hard to locate; rhTSH-stimulated FDG PET-CT may offer a higher sensitivity, particularly when thyroglobulin in high, but its utility has not been clearly established.

Methods: Review of the patient’s clinical record

Results: A 61 years old woman noticed a right anterior neck lump when she was 47; FNAC was suggestive of a solid papillary thyroid carcinoma and she underwent right thyroid lobectomy. The pathology diagnosis was atypical papillary trabecular carcinoma (5.5 cm maximal diameter) with oncocytic changes, with minimal extracapsular invasion but clean surgical margins. She underwent left lobectomy two months later, with normal pathology, followed by ablation with 125 mCi of 131-I one month later, and substitution therapy with levothyroxin ever since. One year afterwards, the rhTSH test was negative, and follow-up thyroglobulin, antithyroglobulin antibodies and neck ultrasonography were negative for the next 9 years. By the tenth year, thyroglobulin was detectable (1.1 ng/mL) and increased in the 11th and 12th years (2.14 and 2.75 ng/mL) but thyroid gammagraphy scans were negative, and ultrasound only revealed unspecific laterocervical adenopathies, with negative FNAC. A CT scan showed only two well-defined pulmonary nodules of 7.5 mm maximum diameter in the lingula and the apical segment of the left lobe. A new rhTSH test with peak TSH of 87.5 mcU/mL showed little response (baseline and stimulated thyroglobulin 5 and 7.5 ng/ml, respectively) with negative stimulated gammagraphy scan. An FDG PET-CT was ordered (13th year) showing only the two known pulmonary nodules, stable in size (both 7.0 mm), without metabolic criteria of malignancy (SUVmax: 1.7). In order to elucidate if the nodules could be metastatic, a new FDG PET-CT was performed (14th year) after rhTSH stimulation, thyroglobulin showed again a modest response (8.25 to 10.4 ng/mL) and the nodules showed a small increase (10 mm) and an increase in metabolic activity under stimulation (SUVmax 1.3 to 2.3). Ablation with 150 mCi of 131-I was performed, but the gammagraphy scan did not show enhancement of the pulmonary nodules. One month afterwards, the patients’s thyroglobulin was not substantially decreased (8.25 to 7.80 ng/mL).

Conclusions: The use of rhTSH-stimulated FDG PET/CT reportedly changes the patients’ management only in a minority of the cases. In our patient, the apparent enhancement of two pulmonary nodules with this technique seems to be a false positive, with negative result of the post-treatment gammagraphy and no change in the patient’s management.