Endocrine Abstracts

Introduction: Thyroid amyloidosis is defined as amyloid protein and fat deposition within the thyroid gland. It is classified as either primary (idiopathic) or secondary to inflammatory/chronic disease. Albeit deposition of amyloid protein in thyroid tissue is frequent, amyloidosis affecting exclusively the thyroid gland without evidence of other organs involved is extremely rare. We report a clinical case of a patient who underwent lobectomy due to a toxic adenoma, whose histology revealed thyroid amyloidosis, without further evidence of systemic involvement, to date.

Clinical case: A 78-year-old male presented to the endocrinology department in January 2018 with thyreotoxicosis, with the laboratory workup confirming a primary hyperthyroidism (TSH 0.05 uU/ml, free T4 1.92 ng/dl, thyroid peroxidase and thyroglobulin antibodies negatives, TRAb 0.80 U/l). There were no other positive findings on the evaluation, namely signs or symptoms of a systemic disease. Thyroid ultrasound revealed a heterogenous thyroid gland, with a single solid nodule with 45 mm on the right lobe. The diagnosis of toxic adenoma was made and the patient underwent right hemithyroidectomy after thyroid function normalization. The histology showed a nodular micro and macrofolicular hyperplasia of the thyroid gland, stroma enlargement, and marked thickening of thyroid vessels wall, with amyloid deposits (positive for Congo red and birefringent in polarized light). The immunohistochemistry was positive for amyloid AA and lambda light chains, and negative for calcitonin and beta 2 microglobulin. Based on morphology and histochemical findings, the diagnosis of thyroid amyloidosis was rendered. Further investigations were carried to check for systemic involvement, including complete autoimmunity panel and biochemical markers of other inflammatory or chronic diseases, all of which were negative. Plasma amyloid precursor was in the normal range. Fat abdominal biopsy was negative for amyloid proteins. The final diagnosis was single thyroid amyloidosis, and the patient maintains a regular follow-up.

Conclusion: Thyroid amyloidosis presented in this clinical case was diagnosed as an incidental finding. Exclusion of systemic involvement is mandatory in this setting, as well as exclusion of a secondary cause of amyloidosis, because most cases of thyroid amyloidosis coexist with involvement of other tissues or organs. This case highlights the rarity of a single thyroid amyloidosis, and the importance of a multidisciplinary approach following a rare diagnosis with an unknown prognosis.