Reappraising the Diagnostic Accuracy of Post-Treatment Whole-Body Scans for Differentiated Thyroid Carcinoma

Multifocal Nonmetastatic Radioactive Iodine Avidity on Whole Body Scan After Thyroidectomy for Thyroid Cancer

Background/Objective

Non-metastatic radioactive iodine (RAI) uptake can complicate the interpretation of whole-body scan (WBS) for differentiated thyroid carcinoma (DTC) post-thyroidectomy. We present a patient with DTC whose follow-up WBS showed nonmetastatic multifocal avidity in skeletal tissue, an uncommonly reported site of RAI uptake.

Case report

A 42-year-old woman underwent a right hemithyroidectomy, followed by completion thyroidectomy and RAI remnant ablation therapy, for a 4.8 cm thyroid tumor consistent with stage pT3aNxMx follicular thyroid cancer. Follow-up WBS showed intense activity in the thyroid bed, right breast, left medial subcortical acetabulum, and several vertebral bodies. Her biochemical and clinical findings were not suggestive of cancer recurrence. Further workup with SPECT/CT and MRI showed no focal vertebral lesions and identified the left femoral lesion as a benign peripheral nerve sheath. Diagnostic mammography and ultrasound showed no evidence of suspicious breast lesions. Neck ultrasound was clear with no suspicious masses or pathologic lymphadenopathy. She remained in remission on continued active surveillance.

Discussion

Nonmetastatic RAI uptake on WBS has many causes, including functional sodium-iodide symporter expression in nonthyroidal tissues, radioiodine accumulation in tissues and bodily fluids, and benign tumors. False-positive uptake can decrease the utility of post-treatment WBS in low-risk patients. Careful clinical examination, biochemical and radiologic follow-up, and close active surveillance can help distinguish false-positive uptake from metastatic or recurrent disease.

Conclusion

We describe an uncommon case of RAI uptake in skeletal tissues after thyroidectomy for DTC, and we outline the steps taken to rule out underlying metastases.

131 I Uptake in a Left Cerebral Infarct on Posttherapy Whole-Body Scan

ABSTRACT

A 75-year-old woman with papillary thyroid carcinoma who underwent 131 I radioiodine treatment was incidentally found to have an established left cerebral infarct demonstrating 131 I uptake on posttherapy whole-body scan. False-positive iodine accumulation can occur in benign processes and other malignancies, necessitating awareness among nuclear medicine physicians to avoid misdiagnosing metastatic disease. SPECT/CT can be utilized to enhance diagnostic accuracy when needed.

Radioiodine whole body scan pitfalls in differentiated thyroid cancer

PURPOSE

whole body scan (WBS) performed following diagnostic or therapeutic administration of I-131 is useful in patients with differentiated thyroid carcinoma. However, it can be falsely positive in various circumstances. We aimed to report a series of pitfalls in a clinical perspective.

METHODS

A search in the database PubMed utilizing the following terms: "false radioiodine uptake" and "false positive iodine 131 scan" has been made in January 2023. Among the 346 studies screened, 230 were included in this review, with a total of 370 cases collected. Physiological uptakes were excluded. For each patient, sex, age, dose of I-131 administered, region and specific organ of uptake and cause of false uptake were evaluated.

RESULTS

370 cases of false radioiodine uptake were reported, 19.1% in the head-neck region, 34.2% in the chest, 14.8% in the abdomen, 20.8% in the pelvis, and 11.1% in the soft tissues and skeletal system. The origin of false radioiodine uptake was referred to non-tumoral diseases in 205/370 cases (55.1%), benign tumors in 108/370 cases (29.5%), malignant tumors in 25/370 cases (6.7%), and other causes in 32/370 cases (8.7%).

CONCLUSIONS

WBS is useful in the follow-up of patients with differentiated thyroid carcinoma, however it can be falsely positive in various circumstances. For this reason, it is critically important to correlate the scintigraphic result with patient's medical history, serum thyroglobulin levels, additional imaging studies and cytologic and/or histologic result.

Papillary Thyroid Microcarcinoma: Insights from a Cohort of 257 Thyroidectomized Patients

Papillary thyroid microcarcinoma management evolved, and less aggressive strategies are now considered. Questions, however, remain on these tumors' behavior, particularly on developing countries' real ground healthcare scenarios. Our aim is to gather insights on the natural history of papillary thyroid microcarcinoma on patients treated with thyroidectomy in Brazil. Consecutive patients diagnosed with papillary thyroid microcarcinoma had their clinical characteristics, interventions, and outcomes described. Patients were classified as incidental or nonincidental based on the diagnosis after or before surgery, respectively. A sum of 257 patients were included, 84.0% of which were women, and the mean age was of 48.3±13.5 years. The mean tumor size was of 0.68±0.26 cm, 30.4% were multifocal, 24.5% had cervical metastasis, and 0.4% distant metastasis. The nonincidental and incidental tumors differed in tumor size (0.72±0.24 and 0.60±0.28 cm, respectively, p=0.003) and in presence of cervical metastasis (31.3% and 11.9%, respectively, p<0.001). Male sex, nonincidental diagnosis, and younger age were independent predictors of cervical metastasis. After 5.5 years (P25-75 2.5-9.7) of follow-up, only 3.8% of patients had persistent structural disease (3.4% cervical). Predictors of persistent disease at multivariate analysis included cervical metastasis and multicentricity. In conclusion, incidental and nonincidental papillary thyroid microcarcinoma patients of the population studied displayed excellent outcomes. Cervical metastasis and multicentricity were frequent findings and prognostic factors for persistent disease.

Treatment strategies for low-risk papillary thyroid carcinoma: a position statement from the Thyroid Department of the Brazilian Society of Endocrinology and Metabolism (SBEM)

Increasingly sensitive diagnostic methods, better understanding of molecular pathophysiology, and well-conducted prospective studies have changed the current approach to patients with thyroid cancer, requiring the implementation of individualized management. Most patients with papillary thyroid carcinoma (PTC) are currently considered to have a low risk of mortality and disease persistence/recurrence. Consequently, current treatment recommendations for these patients include less invasive or intensive therapies. We used the most recent evidence to prepare a position statement providing guidance for decisions regarding the management of patients with low-risk PTC (LRPTC). This document summarizes the criteria defining LRPTC (including considerations regarding changes in the TNM staging system), indications and contraindications for active surveillance, and recommendations for follow-up and surgery. Active surveillance may be an appropriate initial choice in selected patients, and the criteria to recommend this approach are detailed. A section is dedicated to the current evidence regarding lobectomy versus total thyroidectomy and the potential pitfalls of each approach, considering the challenges during long-term follow-up. Indications for radioiodine (RAI) therapy are also addressed, along with the benefits and risks associated with this treatment, patient preparation, and dosage. Finally, this statement presents the best follow-up strategies for LRPTC after lobectomy and total thyroidectomy with or without RAI.

An immediate postoperative response to therapy assessment can help avoid unnecessary RAI therapy

Background

Radioiodine (RAI) therapy plays a vital role in the postoperative treatment of differentiated thyroid cancer (DTC) patients underwent total thyroidectomy (TT). However, even in the presence of capsular invasion and lymph node metastasis prognosis can be excellent and a postoperative RAI treatment might not be necessary for all patients. Therefore, this study explored the criteria for avoiding unnecessary RAI therapy in these patients.

Method

We applied response to therapy assessment immediately after surgery and prospectively recruited 179 excellent or indeterminate response DTC patients with capsular invasion and/or LNM who underwent TT without RAI therapy. During the follow-up, thyroglobulin (Tg), thyroglobulin antibody (TgAb) levels, and cervical ultrasonography were collected and analyzed. Disease-free survival (DFS) was calculated using the Kaplan-Meier method. In addition, response to therapy assessments was performed on patients during each follow-up.

Results

The mean follow-up period was 29.85 ± 17.44 months, and the 3- and 5-year DFS for all the patients was 99.3% in each. At the last follow-up, 165 (92.2%) patients had excellent responses, while 12 (6.7%) had an indeterminate response, and one (0.6%) each had biochemical and incomplete responses. No significant difference was observed in response to therapy between the subgroups of LNM and tumor invasion (P>0.05). For patients with capsular invasion and a number of metastatic lymph nodes ≤5 and >5, the proportions of recorded excellent responses were 95.9%, 91.0%, and 85.7%, respectively. Better responses were observed in females (excellent response: 95.5%, P=0.023), patients with stimulated Tg (s-Tg) ≤1ng/ml (excellent response: 100%, P<0.001), s-Tg ≤ 2ng/ml (excellent response: 98.4%, P<0.001), and excellent response for the immediate postoperative assessment (excellent response: 98.5%, P=0.004).

Conclusions

The current study suggested that the response to therapy assessment immediately applied postoperatively could help avoid unnecessary RAI therapy among DTC patients with capsular invasion and/or LNM. Moreover, excellent response patients and patients with indeterminate response and s-Tg ≤ 2ng/ml could be managed without RAI therapy.