**Author Listing - Lead/ Submitting Author (we will be communicating with this individual): Name, Institution, City and State where the work was done. Co-authors will be added in a separate section.**
Natasha Gorrie, St Vincent's Hospital Sydney, Sydney, NSW

**Main Body of the Abstract**
Background:
Transthyretin amyloidosis(ATTR) prevalence continues to rise due to increased recognition and improved diagnostic techniques. Non-biopsy diagnostic criteria, utilising cardiac bone scintigraphy(BS), has facilitated this, however up to 30% require histopathological confirmation. Histopathological diagnosis is limited by local expertise in biopsy procedures, immunohistochemical assessment, and mass spectrometry access.  Off-target biopsy ATTR diagnostic rates remain poor. Patient factors, including anticoagulation and frailty, and limited access to quaternary centres makes endomyocardial biopsy(EMBX) challenging, hence alternate on-target sites require consideration. We review our centre’s use of non-biopsy criteria, and on- and off-target biopsies for ATTR diagnosis.
Methods:
All patients referred to St Vincent’s Amyloid Clinic between January 2022-2024 were reviewed. Patients were included if ATTR was suspected on histopathology and/or BS. Patients with incomplete work-up or known alternate amyloid subtype were excluded.
Results:
Of 149 patients, 85 suspected ATTR cases were reviewed. Mean age was 79+/-9years, 11 female(13%). All had PYP BS, echocardiography and standard assessment to exclude AL. ATTR was diagnosed in 84(43 ATTRwt, 5 ATTRv, 37 pending/declined genetics), EMBX and repeat BS reclassified one as restrictive cardiomyopathy. Non-invasive diagnostic criteria was met in 60.7%(51). On-target biopsy confirmed diagnosis in 31%; 13 EMBX, 8 tenosynovial, 2 bowel, 1 lung, 1 bladder. Five patients await tenosynovial biopsy results. Off-target biopsy was non-diagnostic in all attempted cases (4 salivary gland, 3 fat-pad).
Conclusion:
Our study demonstrates the diagnostic challenges of ATTR. Histopathological confirmation remains necessary in a significant population and alternative biopsy sites require consideration, especially in high-risk patients or with limited EMBX access.



Diagnosing Transthyretin Amyloidosis: A single centre experience with histopathological diagnosis PB91 (#553)

We invite you to attend the XIX International Symposium on Amyloidosis to be held in Rochester, MN.

This symposium is organized as a hybrid meeting (with the focus on in-person) held from Sunday, May 26 through Thursday, May 30, 2024.

Together with the ISA Board and members of Mayo Clinic, a very attractive scientific hybrid program is being planned. The program will cover a variety of types of systemic amyloidosis: ATTR (hereditary and wild-type), AL (light-chain), AA and less frequent forms. There will be key lectures, specific symposia including those company sponsored, oral presentations and poster sessions of accepted abstracts.

COURSE DESCRIPTION
This program will provide a comprehensive review of state-of-the-art education in systemic amyloidosis: basic science, pathophysiology, diagnosis, current and emerging treatments. Scientific presentations will include competitive oral and poster abstracts. The rapid evolution of scientific discovery and expanding treatment options has created tremendous interest in the field and this meeting will fill and important gap in educating scientists and clinicians.