AIns (insulin) type amyloidoma of the extremity diagnosed by fine-needle aspiration.

Amyloid is an extracellular deposition of Congo red positive material which shows apple green birefringence under polarized light. A cytopathologist can uncommonly encounter such cases. Among the reported cases, a fine-needle aspiration (FNA) of amyloid is frequently misinterpreted as acellular nondiagnostic material. We report a case of amyloidoma of the right upper arm in a 68-year-old man with history of renal transplantation for diabetic nephropathy who presented with loss of appetite and weight loss. Physical exam showed a 7 cm hard nodular subcutaneous mass in the right upper arm. FNA yielded abundant acellular, irregular fragments of dense material, which was Congo red positive with apple green birefringence by polarized light, consistent with amyloid. Further subtyping of the amyloid by mass spectrometry, showed AIns (insulin)-type amyloid deposition. After further questioning, the patient admitted to injecting insulin at the same site for many years. Awareness of the cytological features is important for diagnosis. This is especially important when dealing with uncommon sites and without adequate clinical information.