Background: Systemic amyloidosis (SA) is often diagnosed late. Combining clinical and biochemical biomarkers is necessary for raising suspicion. Fine needle aspiration (FNA) of subcutaneous fat enables SA detection by Congo red staining. The luminescent conjugated probe heptameric thiophene acetic acid (h-FTAA) is a sensitive alternative to Congo red-staining of tissue samples.
Objective: To compare h-FTAA fluorescence with the Congo red stain for amyloid detection in FNA-obtained fat tissue.
Methods: 57 patients with established SA were studied (19 with AA, 20 with AL, and 18 with ATTR) and 17 age-matched controls (34-75 yrs). h-FTAA positivity was graded according to a Congo red-based grading scale ranging from 0 to 4+.
Results: Amyloid grading by both methods correlated strongly (r=0.86, p<0.0001). h-FTAA was positive in 51 of 52 Congo red positive cases (sensitivity 98%). h-FTAA was negative in 7 of 17 Congo red negative controls (specificity 41%), but was also positive for 5 Congo red negative SA cases.
Conclusions: h-FTAA fluorescence is more sensitive than Congo red staining in this small exploratory study of fat tissue samples, implicating potential sensitivity for prodromal amyloidosis, but is less specific for clinical amyloidosis. h-FTAA staining may therefore be the most appropriate method for screening fat tissue samples but should presently treat grade 1+ as only suggestive, whereas 2+ or higher as positive for amyloidosis.