Clinical presentation: a 52-year-old woman was referred for an evaluation of hyperthyroidism.

Palpation: both thyroids were enlarged and moderately firm. No nodule was palpable.

Results of blood tests: moderate degree of hyperthyroidism (TSH-level undetectable, FT4 37.1 pM/L, FT3 7.99 pM/L), anti-TPO < 10 IU/ml, TSAb-assay negative.

Ultrasonography: the thyroid was moderately hypoechogenic without any circumscribed lesions. The vascularization was decreased.

Cytological picture: no colloid can be found in the background. Thyrocytes are in small clusters, microfollicles and dissociated. Almost all follicular cells exhibit oxyphilic metaplasia. A great number of inclusions can be observed. There are only a few lymphocytes in the background. The cytological picture would be more than suspicious for oxyphilic variant of papillary cancer. However, the patient had no nodule in the thyroid.

Combined clinical-ultrasonographic-cytological diagnosis: benign Hashimoto's thyroiditis, hashitoxicosis.

Follow-up investigation: we performed antibody determination, and both the TSH-receptor antibody and the anti-TPO level were normal. 3 months later the patient presented subclinical hypothyroidism while 12 month later overt hypothyroidism has developed. The patient moved to another town and visited another thyroidologist. She reviewed her previous medical reports and offered surgery because of the original cytological description ("numerous inclusions") and the negative anti-TPO titer.

Histopathology: benign Hashimoto's thyroiditis.

Comments.

1. The indication of FNAC was the differential-diagnosis of hyperthyroid state. The decreased vascularization on Doppler method favoured the possibility of Hashitoxicosis, while the cytology answered the question.

2. The FNAC pattern itself was suspicious for a Hürthle-cell tumor and even a papillary cancer could not be excluded. Nevertheless, the patient had no nodule. Theoretically, we could imagine that we accidentally aspirated a focus of a papillary microcancer less than 1 mm. However, this possibility was only theoretical. Moreover, we had to consider in this theoretical situation the chance that the patient would suffer any harm if she was not  operated: it is practically zero..

3. This case was an example which demonstrated the need for a new diagnostic system. In certain cases, only a common diagnosis based on clinical, sonographic and cytologic data can be correct.

4. And last, we must be aware that the sensitivity of anti-TPO determination is only around 90%.