Scintigraphy or fine-needle aspiration biopsy to exclude thyroid malignancy: what should be done first in iodine deficiency?

Evaluation of thyroid nodules--combined use of (99m)Tc-methylisobutylnitrile scintigraphy and aspiration cytology to assess risk of malignancy and stratify patients for surgical or nonsurgical therapy--a retrospective cohort study

OBJECTIVE

Thyroid nodules are a common clinical problem, and differentiation between benign and malignant nodules is essential. The aim of this study was to evaluate an approach for cold thyroid nodules including (99m)Tc-methylisobutylnitrile (MIBI) scintigraphy to assess risk of malignancy and stratify patients for therapy.

DESIGN

Retrospective cohort study; 391 patients with at least one cold thyroid nodule were consecutively admitted (between 1 January 2004 and 31 December 2006) and recommended for surgical or nonsurgical therapy.

MEASUREMENTS

Thyroid ultrasonography, (99m)Tc-pertechnetate scintigraphy, laboratory tests, fine needle aspiration cytology (FNAC) and MIBI scintigraphy.

RESULTS

57·3% (224/391) had one cold nodule, 17·9% (70/391) had several cold nodules, and 24·8% (97/391) had both cold and hot nodules. MIBI scintigraphy was classified into 'positive' (16·1%, 63/391), 'weakly positive' (19·2%, 75/391) or 'negative' (64·7%, 253/391). FNAC was classified into benign (87·9%, 247/281), nondiagnostic (6·8%, 19/281) or suspicious/malignant (5·3%, 15/281). 127 patients received surgery, revealing malignancy in 13·3% (17/127), predominantly papillary (64·7%, 11/17) and follicular carcinoma (23·5%, 4/17). MIBI scintigraphy was 'positive' (64·7%, 11/17) or 'weakly positive' (23·5%, 4/17) in most patients with malignant findings. FNAC was unavailable in 23·5% (4/17) with malignancy, positive in 38·5% (5/13) and negative in 61·5% (8/13). Among patients undergoing surgery, sensitivity, specificity, negative and positive predictive values for MIBI scintigraphy were 88·2%, 35·5%, 95·1% and 17·4%, for FNAC 38·5%, 90·6%, 90·6% and 38·5%, respectively, and for the combination (MIBI scan + FNAC) 92·3%, 30·6%, 96·3% and 16·9%. Benign MIBI-positive nodules were predominantly follicular adenomas (68%, 33/48).

CONCLUSION

Evaluation of cold thyroid nodules by MIBI scintigraphy aids therapeutic decisions: MIBI-negative findings support nonsurgical management in about two-thirds of patients, while MIBI-positive findings have an increased risk of malignancy, supporting surgical therapy. However, the positive predictive value was low, which requires further research.

[Scintigraphically "hot" thyroid nodules mainly go hand in hand with a normal TSH]

AIM

In recent years, various professional societies published guidelines for diagnostic evaluation of thyroid nodules, in which the indication for scintigraphy is restricted to patients with subnormal TSH values. It is seen controversial whether such recommendations should be transferred to Germany, partly because of lower iodine intake in this country and the consequent higher percentage of autonomous thyroid nodules, which are not accompanied by a measurable dysfunction. Since reliable data to this topic are scarce, we analyzed multicentrically the spectrum of scintigraphically "hot" and "warm" nodules under the current epidemiological conditions.

PATIENTS, METHODS

In 10 German nuclear medicine out-patient institutions we evaluated the diagnostic data from a total of 514 patients, in whom unequivocally hyperfunctional nodules (focal increased uptake in comparison to perinodular tissue with a sonographically nodular correlative ≥1 cm) could be detected by (99m)Tc-pertechnetate scintigraphy. To minimize selection bias, the surveys were not carried out in hospitals.The recorded parameters included the thyroid hormone levels, the global (99m)Tc-uptake (TcTU), the size of each nodule and the total autonomous nodular volume (V(aut)).

RESULTS

Only 20% of the patients with "hot" nodules had subnormal TSH levels (<0.1 to 0.33 mU / l), the remaining patients had TSH levels from 0.34 to 3.5 mU /l (in one third of the patients TSH levels even exceeded 1.0 mU/l). Moreover, we found no relevant correlation between TSH and TcTU or V(aut).

CONCLUSIONS

In Germany, in at far the largest proportion of patients with autonomous thyroid nodules objectified by means of scintigraphy, TSH levels are within the normal range. Since such nodules with maximum safety can be classified as benign, a corresponding scintigraphic finding has a high priority for the patient. These current data support that it is not reasonable to restrict scintigraphy to patients with subnormal TSH values in this country.