Distinctive Patterns of Transthyretin Amyloid in Salivary Tissue

Accurate typing of amyloidosis is still a major issue for pathologists and clinicians. Besides clinical data and immunohistochemistry, the histologic distribution of amyloid could represent a useful tool to prevent typing errors, such as the misdiagnosis of hereditary and senile amyloidosis as light chain-related amyloidosis (AL). Minor salivary gland biopsy (MSGB) is a widely performed procedure for amyloidosis diagnosis and typing. In the largest clinicopathologic series of amyloid-containing MSGB specimens to date, we investigated for the first time whether amyloidosis subtypes can be distinguished according to their pattern of salivary amyloid deposition. The histologic distribution and semiquantification of amyloid within salivary tissue were thoroughly reassessed for each case using Congo red-fluorescence. Clinical data were retrospectively collected. The cohort included 92 patients with amyloid-containing minor salivary gland biopsies. The type of amyloidosis was AL in 51 patients (55.4%), non-V30M mutant ATTR in 10 (10.9%), V30M mutant ATTR in 8 (8.7%), serum amyloid A-derived amyloidosis (AA) in 6 (6.5%), wild-type ATTR in 4 (4.3%), gelsolin in 3 (3.3%), and unclassified in 10 (10.9%). Amyloid was more abundant in AL and AA compared with ATTR amyloidosis, because of more extensive basement membranes and vascular deposits. Conversely, non-V30M mutant ATTR and wt-ATTR were strongly associated with peculiar amyloid nodules located in close contact with salivary excretory ducts, with a specificity of 91.7%. In conclusion, our study suggests for the first time that MSGB, in addition to its high sensitivity for amyloidosis diagnosis, is a simple and effective tool for the recognition of ATTR amyloidosis.