Granulomatous thyroiditis coexistent with multinodular goiter with clinical, biochemical, scintigraphic and ultrasound features mimicking autonomous adenoma.

A 35-years-old women was referred to our Endocrinology Unit for multinodular goiter diagnosed 2 years before, presenting with a prevalent nodule in the left thyroid lobe and mild symptoms of dysphagia. The patient did not report spontaneous or palpation-induced pain in the neck and no clinical signs of overt thyrotoxicosis were present. Normal free thyroxine (9.9 pg/ml), free tri-iodothyronine (2.13 pg/ml) and reduced serum TSH concentration (0.12 mU/L) with undetectable anti-thyroid autoantibodies were found. Thyroid ultrasonography (US) and color flow Doppler sonography (CFDS), 99mTC scintiscan were performed. Thyroid US and CFDS revealed in the left lobe a prevalent hypoechoic hypervascularized nodule of 26x12 mm of diameters with increased intranodular blood flow (type III pattern); other smaller nodules with similar US features were present in both thyroid lobes. The extranodular tissue of the gland was normoechoic with normal vascularity at CFDS examination. 99m Tc thyroid scan showed an increased uptake corresponding to the left prevalent nodule and nearly absent uptake in the remaining thyroid tissue. The presence of an autonomous pre-toxic nodule in the context of a multinodular goiter was diagnosed, and the patient was then submitted to total thyroidectomy. Histological examination revealed several hyperplastic bilateral nodules without pathological features of adenomas, including the main nodule of the left lobe. Surprisingly, the extranodular thyroid tissue of the right lobe showed multiple foci of diffuse lymphocytes, plasma cells and multinuclear giants cells infiltration. A mild patchy inflammation of similar morphology was also present in the left lobe. Interestingly, all the thyroid nodules were exent from any inflammatory disease. This histological pattern suggests that a destructive process (granulomatous thyroiditis) may have inhibited thyroid function of the extranodular tissue, while the normally functioning nodular hyperplastic tissue of the left lobe, unaffected by the inflammatory process, mimicked a “hot” nodule. The precise nature of granulomatous thyroiditis could not be established in this case: the absence of pain and general symptoms are in keeping with a diagnosis of painless subacute thyroiditis. Suppressed TSH (typical of the hyperthyroidism phase of subacute thyroiditis) adds further evidence in favour of this hypothesis, although other granulomatous processes (like sarcoidosis) may also cause transient destructive thyrotoxicosis. Further investigations aimed to exclude systemic granulomatous disease and long-term follow-up will be needed to better define the diagnosis of this unusual case.