Scintigraphic Patterns in Patients with Subclinical Hyperthyroidism

Abstract

The occurrence of suppressed thyroid stimulating hormone (TSH) levels in the presence of normal free thyroxine (fT4) and free triiodothyronine (fT3) is not rare. Although this entity may be defined as "subclinical hyperthyroidism", many patients presented with the above laboratory findings, suffer from non-specific signs and symptoms that could be related to hyperthyroidism. The aim of this study was to evaluate this entity using the standard method of radionuclide thyroid imaging by 99mTc-pertechnetate (99mTcO<inf>4</inf>-). Fifty-two patients (18 males; mean age: 45±9 years and 34 females; mean age: 43± 11 years) with suppressed serum TSH levels and normal fT3 and fT4 levels, who were referred to our nuclear medicine department for thyroid scintigraphy were prospectively included in the study. Any thyroidal or non-thyroidal medication, thyroid surgery or non-thyroidal diseases constituted the main exclusion criteria. Thyroid scintigraphy was performed 15 min after the i.v. injection of 111 MBq 99mTcO<inf>4</inf>- using a pinhole collimator. Scintigraphic findings were visually evaluated. All patients had normal serum levels of fT4 (mean value 1.53±0.14 ng/dl, normal range: 0.89-1.8 ng/dl) and fT3 (mean value 3.9±0.17 ng/dl, normal range: 2.3-4.2 ng/dl). Mean value ot serum TSH levels was 0.09±0.12 μIU/ml (normal range: 0.35-5.5 μIU/ml). The above hormones were tested by the chemiluminescent method. Patients showed seven different scintigraphic patterns in their thyroid scintigrams as follows: hyperactive+hypoactive multinodular goiters, 27%; hyperactive multinodular goiters, 23%; hypoactive multinodular goiters, 15%; solitary hypoactive nodular glands, 14%; normal glands, 9%; solitary hyperactive nodular glands, 8%; and diffuse hyperactive glands, 4%. All but two patients (50/52 = 96%) showed mild to moderate hyperplasia of the thyroid gland. It is concluded that most patients with subclinical hyperthyroidism, (96%) show mild to moderate hyperplasia of the thyroid, and many (65%) show multinodularity with at least one hyperactive nodule.