Distribution of Functional Status of Thyroid Nodules and Malignancy Rates of Hyperfunctioning and Hypofunctioning Thyroid Nodules in Germany

AIM

Thyroid scintigraphy enables the depiction of the functional status of thyroid nodules (TNs) with both, ^99mTc-pertechnetate and ¹²³Iodine. The functional status is relevant for diagnostic procedures for the differentiation of benign and malignant TNs. The aim of this study was to examine the current frequencies of hyper-, hypo- and isofunctioning TNs in Germany and to estimate the risk of malignancy with regard to functional status.

METHODS

In 11 study centers, a minimum of 100 nodules per center were consecutively enrolled between July 2019 and April 2020. Inclusion criteria were: newly diagnosed nodule, nodule' size of 10 mm or more, thyroid scintigraphy. Exclusion criteria were: completely cystic TNs, patients with prior radioiodine therapy or thyroid surgery. The risk of malignancy was estimated for hyper- and hypofunctioning TNs.

RESULTS

Overall, 849 patients (72 % women) with 1262 TNs were included. Patients' age ranged from 18 to 90 years. Most TNs were hypofunctioning (n=535, 42%) followed by isofunctioning TNs (n=488, 39%) and hyperfunctioning TNs (n=239, 19%). When only TNs with a maximum size of 2 cm or more were considered the rate of hyperfunctioning and hypofunctioning TNs increased (to 27% and 49%) while isofunctioning TNs decreased. Only one of all hyperfunctioning TNs was malignant. In hypofunctioning nodules, the malignancy rate was estimated at 10%.

CONCLUSION

In Germany, the proportion of hyperfunctioning TNs is approximately 20% and increases in larger TNs to up to 27%. Due to the low risk of malignancy in hyperfunctioning TNs, no further procedures to rule out malignancy are necessary. The risk of malignancy of hypofunctioning TNs is significantly higher. Thus, a thyroid scintigraphy is a useful diagnostic tool in Germany.

The role of nuclear medicine in differentiated thyroid cancer

In differentiated thyroid cancer (DTC) nuclear medicine is able to cover the spectrum from diagnosis and treatment to follow up keeping patient's management in one institution. Nowadays, DTC is often diagnosed per chance, presenting as small indolent nodule diagnosed on routinely performed ultrasound. Ultrasound and ultrasonography-guided fine-needle aspiration biopsy together with scintigraphy are probably the most adequate tools for diagnosis. After thyroidectomy, treatment with iodine-131 is routinely performed in a nuclear medicine therapy institution as a standard procedure in most of the cases with regard to histology. In case of iodine positive metastases, repeated therapies can be performed in order to reduce tumour burden. In the follow up of DTC thyroglobulin (tumour marker), ultrasound and diagnostic whole body scan are established procedures. With the development of SPECT/CT and PET/CT ((18)F-FDG, (68)Ga-somatostatin receptor) combining functional and anatomic imaging the nuclear medicine spectrum has further increased.

Multinodular goitre: 'much more to it than simply iodine deficiency'

For over a century, multinodular goitre (MNG) has been looked upon as the simple consequence of iodine deficiency. This view is now no longer tenable. Indeed, many characteristics of MNG do not fit with the iodine deficiency concept. For example, nodular goitre is a frequent disease even in those countries where the population is never exposed to iodine shortage. Moreover, neither multinodularity, nor the proverbial heterogeneity of growth and function or the autonomous, thyroid stimulating hormone (TSH)-independent growth of many goitres are compatible with the iodine deficiency concept, let alone subclinical or overt thyrotoxicosis which often complicates the course of a MNG. Recent investigations have led to the conclusion that MNGs are true benign neoplasias that are due to the high intrinsic growth potential of a variable, genetically predetermined fraction of all thyrocytes. Gross and heritable metabolic and functional differences between the individual thyrocytes, from which new follicles are generated during goitrogenesis, are the cause of the often spectacular functional and structural heterogeneity of MNG. Superimposed iodine deficiency changes the epidemiology, but not the basic mechanisms of goitrogenesis. These new pathogenetic concepts have a profound impact on the clinical management of MNG.