Dual Diagnosis of Thyroid Amyloidosis and Lipomatosis: An Uncommon Concurrence

Lipoid lesions of the thyroid are extremely rare. Adipose changes can be seen in both malignant (carcinomas) and benign conditions. The two most common benign entities are thyrolipoma and thyrolipomatosis, which have been reportedly associated with systemic amyloidosis. Radiologically, these lesions can mimic malignancy, especially when presenting as a biochemically active condition. We present a rare case of concurrent thyroid lipomatosis and serum amyloid A amyloidosis (AA) manifesting as goiter and subclinical hyperthyroidism. A 72-year-old male presented to Danbury Hospital with complaints of hoarseness of voice and reduced neck movement. His past medical history was significant for Crohn's disease, ankylosing spondylitis, monoclonal gammopathy of undetermined significance (MGUS), and AA amyloidosis involving bilateral kidneys with end-stage kidney disease (ESKD) status post renal transplantation. AA amyloidosis secondary to Crohn's disease led to bilateral kidney involvement and ESKD, requiring renal transplantation. Fine-needle aspiration of the left lower lobe in 2021 confirmed thyroid gland involvement, revealing atypical follicular cells with colloid present, classified as Bethesda Category III, with Congo red staining demonstrating amyloid deposition. Physical examination revealed severely enlarged thyroid glands causing compressive symptoms. Thyroid function tests indicated subclinical hyperthyroidism. Thyroid ultrasound revealed a right lobe measuring 9.0 × 5.5 × 4.8 cm and a left lobe measuring 9.0 × 5.5 × 4.3 cm, with a bilateral increase in size compared to imaging from two years prior. The left thyroid gland had a lower pole hypoechoic nodule measuring 1.0 × 1.0 × 0.8 cm, with mixed cystic and solid composition and smooth margins. No pathologically enlarged or morphologically abnormal cervical lymph nodes were identified on imaging. On follow-up, a total thyroidectomy with intraoperative nerve monitoring was performed. During follow-up in 2024, sonographically guided fine-needle aspiration of the left lower pole thyroid nodule was classified as unsatisfactory (Bethesda Category I), showing sheets of degenerated and anucleated squamous cells with debris, but no follicular cells. Thyroidectomy was subsequently performed due to symptomatic goiter with compressive symptoms. Gross examination of the specimen showed an abnormally enlarged thyroid gland with a diffusely yellowish cut surface. Hematoxylin and eosin (H&E) staining showed eosinophilic, amorphous, extracellular deposits, with diffuse infiltration of mature adipocytes in the thyroid stroma. A few entrapped residual thyroid follicles were observed. Congo red stain confirmed amyloid deposition, exhibiting apple-green birefringence under polarized light. Thyroid amyloid deposits are rare. Associated with chronic inflammatory conditions, including rheumatoid arthritis, ankylosing spondylitis, Crohn's disease, and familial Mediterranean fever (FMF). This case study illustrates the rare concurrence of thyroid lipomatosis and AA amyloidosis. It is thought that chronic hypoxia from AA amyloid-induced capillary damage: the driver of fibroblast-to-adipocyte metaplasia. Progression of this process resulted in diffuse replacement of the thyroid parenchyma with adipocytes and goitrous enlargement requiring resection.