Amyloid goiter: cytomorphological features and differential diagnosis on fine needle aspiration cytology: a case report.

Background: Amyloid goiter is a rare cause of thyroid enlargement which can be confused clinically as well as cytologically with both colloid goiter and neoplastic process of thyroid.

Case: A 30-year-old man, diagnosed with chronic kidney disease 5 months previously and currently on dialysis and awaiting renal transplant, was referred by clinicians for fine needle aspiration cytology (FNAC) for thyroid swelling. FNAC showed dense amorphous clumps of extracellular material which appeared magenta colored on Giemsa and eosinophilic on Papanicolaou stain. Congo red staining and polarization showed characteristic apple green birefringence, thus confirming the material as amyloid, and the diagnosis of amyloid goiter was made.

Conclusion: Amyloid on FNAC smears can be easily mistaken for colloid, and correct interpretation can avoid a false diagnosis of colloid goiter. A search should be made to look for any features suggestive of medullary carcinoma of the thyroid as amyloid is more often associated with it.