The association of Hashimoto disease and Congo red negative amyloidosis.

Systemic amyloidosis which is characterized by extracellular deposition of monoclonal immunoglobulin light chains in various organs may be difficult to diagnose at an early stage, especially when the Congo red stain is negative. We describe herein a case of Congo red negative primary amyloidosis associated with Hashimoto thyroiditis. The patient presented with multiple organ involvement suggestive of amyloidosis including heart failure, renal failure, and macroglossia. Serum and urine immunofixation studies were positive for monoclonal chains. Even though a biopsy taken from the enlarged tongue of the patient was negative when stained with Congo red, electron microscopy showed ultrastructural features of amyloid deposition. In conclusion, we are reporting a rare case of primary amyloidosis with a negative Congo red stain associated with Hashimoto thyroiditis.