Amyloidosis is a heterogenous syndrome characterized by the deposition of eosinophilic amorphous extracellular material consisting of insoluble misfolded proteins in a single or multiple organs. Primary or Amyloid L (AL) amyloidosis, which is characterized by the accumulation of monoclonal immunoglobulin light chain fibrils, is the most common systemic form. Thyroid involvement is quite common in systemic amyloidosis, although amyloid goiter is rarely encountered.

A case of a 63-year-old man with a history of AL amyloidosis with end stage renal disease and symptomatic substernal goiter is presented. The patient complained about progressing cervical swelling, dyspnea and neck discomfort and a large multinodular goiter was evident on palpation. Magnetic resonance imaging (MRI) revealed a diffusely enlarged gland with extension to the anterior mediastinum which encased the trachea, causing partial constriction.

Total cervical thyroidectomy was performed, where the parenchyma was found hemorrhagic and friable, thus contributing to the complexity of the operation. Histological examination revealed a diffusely enlarged, nodular gland with abundant parenchymal amyloid depositions and adipose tissue infiltration, without signs of malignancy, attesting the diagnosis of amyloid goiter.

Although thyroid participation is very common in various amyloidosis types, goiter formation resulting from significant amyloid accumulation is described as rarely as in 0.04% of AL amyloidosis cases. While thyroid function is usually preserved, compressive symptoms may be present. Diagnosis can be facilitated by fine needle aspiration and management includes both surgical excision and amyloidosis treatment.