Correlation between anti-thyroid peroxidase antibody levels and diffuse thyroid uptake of 18F-fluorodeoxyglucose in Hashimoto's thyroiditis: a retrospective study

The role of PET/CT in thyroid autoimmune diseases

Autoimmune thyroid diseases (AITD) are a heterogeneous group of disorders. They include, in particular, Graves' disease and Hashimoto's thyroiditis with a wide range of different functional status ranging from subclinical biochemical abnormalities to severe hyperthyroidism or severe hypothyroidism respectively. Furthermore, other conditions more frequently infectious or drug related can cause an immune reaction in the thyroid tissue. In AITDs, positron emission tomography/computed tomography (PET/CT) does not play a primary role for disease diagnosis or management, but accidental findings can occur in both symptomatic and asymptomatic patients, and they should be recognized and well interpreted. A comprehensive literature search of the PubMed databases was conducted to identify papers (systematic review, prospective and retrospective study, case report) evaluating the role of PET/CT in thyroid autoimmune diseases. Thyroid diffuse uptake of 18F-fluoro-2-deoxy-2-d-glucose ([18F]FDG) has been shown to be frequently associated with AITDs, but also with immune-induced thyroid disorders related to SARS-CoV-2 or immunotherapy, while malignant lesions more often have a focal aspect. Other radiopharmaceuticals as [68Ga]-DOTA-peptides, [68Ga]-fibroblast activation protein inhibitors (FAPIs) and [68Ga]-prostate specific membrane antigen ([68Ga]-PSMA) showed similar findings. In conclusion, PET/CT scan in AITDs does not play a primary role in the diagnosis, but the occasional finding of a thyroid uptake must always be described in the report and possibly investigated for a better patient's management.

Thyroid 18F-fluorocholine uptake in patients with chronic autoimmune thyroiditis

Objective

18F-Fluorocholine (18FCH) PET/CT has high sensitivity for parathyroid adenoma detection and can reliably exclude malignancy in thyroid nodules with indeterminate cytology. Data regarding 18FCH uptake in chronic autoimmune thyroiditis (CAT) are scarce. We aimed to assess thyroid 18FCH uptake in CAT with biological and histological correlation.

Methods

This is an ancillary study from the Chocolate trial (NCT02784223) that prospectively enrolled 107 patients planned for thyroid surgery. 18FCH PET/CT acquisitions were performed 20 and 60 min after injection. 18FCH uptake in the thyroid gland was assessed by measuring maximum (SUVmax) and mean (SUVmean) standardized uptake values. Thyrotropin, free thyroxine (FT4), thyroid peroxidase antibodies (TPOAb) and thyroglobulin antibodies were collected. The intensity of thyroiditis and the degree of fibrosis were assessed on pathology.

Results

CAT was evidenced in 19/107 (18%) patients. Of these, 13 (68%) displayed an increased and diffuse 18FCH thyroid uptake. This uptake pattern was not observed in patients without CAT. SUVmax and SUVmean were higher in patients with CAT than in those without (P < 0.001). At both acquisition times, SUVmax showed a monotonic relationship with the intensity of thyroiditis (Spearman ρ = 0.44 and 0.51, respectively, P < 0.001) and with the degree of fibrosis (Spearman ρ = 0.55 and 0.62, respectively, P < 0.001). SUVmax showed a linear relationship with TPOAb titers at 20 min (Pearson r = 0.54, P < 0.05; Spearman ρ = 0.59, P = 0.03).

Conclusions

More than two-thirds of the patients with CAT present high and diffuse thyroid 18FCH uptake. This uptake pattern is highly specific to CAT and is correlated with pathology and TPOAb titers.

Pembrolizumab-Induced Thyroiditis Shows PD-L1Expressing Histiocytes and Infiltrating T Cells in Thyroid Tissue - A Case Report

Context

Immune-related adverse events frequently take place after initiation of immune checkpoint inhibitors (ICI) therapy. The thyroid gland is the endocrine organ most commonly affected by ICI therapy, the pathological mechanism is still poorly understood.

Case Description

A 60-year old Upper Austrian male melanoma patient under pembrolizumab therapy received thyroidectomy because of a suspicious FDG avid thyroid nodule. Histopathology showed a pattern comparable with thyroiditis de Quervain. The inflammatory process consisted predominantly of T lymphocytes with a dominance of CD4+ T helper cells. In addition CD68+ histiocytes co-expressing PD-L1 were observed.

Conclusion

Clusters of perifollicular histiocytes expressing PD-L1 were observed in this case of pembrolizumab induced thyroiditis - probably induced by the former ICI therapy. This finding might indicate the initial target for the breakdown of self tolerance. In context with other data the immunological process seems to be driven by CD3+ lymphocytes infiltrating the thyroid.

Increased thyroid uptake on 18F-FDG PET/CT is associated with the development of permanent hypothyroidism in stage IV melanoma patients treated with anti-PD-1 antibodies

PURPOSE

To determine performances of 2-deoxy-2-(18F)fluoro-D-glucose (18F-FDG) positron emission tomography (PET) to detect the development of permanent thyroid dysfunction (PTD), and to evaluate the prognostic value of early increased thyroid uptake in stage IV melanoma patients treated with anti-programmed death 1 (anti-PD-1) antibodies.

METHODS

Twenty-nine patients were retrospectively enrolled. PTD was defined as symptomatic thyroid disorder requiring long-term specific treatment. On the first PET performed during follow-up, maximal standardized uptake value of the thyroid (SUVmax-Th) and SUVmax-Th/SUVmax-blood-pool ratio (Th/B) were measured. Areas under ROC curves (AUC) of these parameters for the diagnostic of PTD were compared. Cutoff values were defined to maximize the Youden's index. Survival analyses were performed according to the Kaplan-Meier method and compared using the log-rank method between patients with and without enhanced thyroid uptake according to cutoff values defined with the Hothorn and Lausen method.

RESULTS

Four patients presented PTD. Median SUVmax-Th and Th/B were, respectively, 2.11 and 1.00. The median follow-up period was 21.7 months. AUC were 1.0 (CI_95% 0.88-1.0) for both parameters. Optimal cutoff values were, respectively, SUVmax-Th > 4.1 and Th/B > 2.0, both conferring sensitivities of 100% (CI_95% 40-100%) and specificities of 100% (CI_95% 86-100%). The median progression-free survival and overall survival were 11.3 months and 33.5 months, respectively. Using optimized cutoffs, there was no statistically significant difference of survival.

CONCLUSION

SUVmax-Th > 4.1 and Th/B > 2.0 provided perfect diagnostic performances to detect patients that developed PTD. No significant survival difference was found between patients with and without increased thyroid uptake.

Detection of thyroiditis on PET/CT imaging: a systematic review

PURPOSE

The incidence and clinical significance of thyroiditis detected by molecular imaging methods is a clinical challenge that is not widely investigated in the literature. The aim of this systematic review was to analyze published data about the detection of thyroiditis on PET or PET/CT using different tracers.

METHODS

A comprehensive computer literature search of the Scopus, PubMed/MEDLINE, Embase, and Cochrane library databases was conducted up to November 2019 to find relevant papers on the detection of thyroiditis by PET/CT, the metabolic appearance, and the clinical significance.

RESULTS

Twenty-six articles were selected and retrieved in full-text version. From the analyses of these studies, the following main findings have been found. Diffuse thyroid uptake of PET tracers is a relatively frequent event, ranging from 0.4 to 46.2%, and it is commonly related to benign disease. Thyroiditis is the most frequent reason for diffuse increased thyroid ¹⁸F-FDG uptake. Cases of malignant disease with a pattern of diffuse ¹⁸F-FDG thyroid uptake are less frequent. Preliminary studies show a possible role of thyroiditis detected by ¹⁸F-FDG PET/CT in evaluating treatment response and as a prognostic marker in oncological patients treated with immunotherapy. However, further studies are needed.

CONCLUSIONS

Diffuse ¹⁸F-FDG thyroid uptake is a relatively rare event commonly due to benign diseases, among which thyroiditis is the most common. The rate of neoplastic disease with diffuse ¹⁸F-FDG thyroid uptake is very low. Diffuse ¹⁸F-FDG thyroid uptake requires further investigation and clinical evaluation for the correct diagnosis. Currently, cases of diffuse thyroid uptake with non-¹⁸F-FDG radiotracer are only anecdotal.