Localized Nodular Amyloidosis of the Buccal Mucosa Associated with Sjögren's Syndrome: A Case Report and Literature Review.

Amyloidosis is a group of disorders in which specific precursor proteins form insoluble amyloid fibrils are deposited in various organs and extracellular spaces. Sjögren's syndrome (SS) is a chronic inflammatory disease in which lymphocytes infiltrate the exocrine glands, such as the salivary and lacrimal glands, through an autoimmune mechanism. At advanced stages of SS, localized nodular amyloidosis has been reported in specific organs outside the glands. Herein, we report a case of localized nodular amyloidosis associated with SS. An 80-year-old woman, who had been biting her buccal mucosa for several years and was aware of the presence of a mass, which had increased in size since approximately 6 months, was referred to our hospital. The patient had a history of SS and systemic lupus erythematosus since her 50s. A needle biopsy was performed because malignancy was suspected by magnetic resonance imaging. The pathological diagnosis was ATTR-type amyloidosis. The patient underwent excision of the lesion to improve the swelling. The pathological findings showed plasma cell infiltration in some areas, which required differentiation from AL amyloidosis; therefore, the patient was referred to a facility specializing in amyloidosis. The pathological diagnosis was AL amyloidosis. Various clinical findings ruled out systemic involvement and the final pathological diagnosis was localized nodular amyloidosis. It has been reported that it may occur in the advanced stages of SS, and our patient had SS for 30 years. One year after the surgery, the patient's prognosis was good.