Steep increase in the number of transthyretin-positive cardiac biopsy cases in Japan: evidence obtained by the nation-wide pathology consultation for the typing diagnosis of amyloidosis.

Background: In 2019, 2020 and 2022, the Japanese Government approved the use of tafamidis and two technetium-scintigraphies for transthyretin amyloid (ATTR) cardiomyopathy, and announced the patient criteria for tafamidis therapy. In 2018, we had started a nation-wide pathology consultation of amyloidosis.

Objective: To reveal the impact of approval of tafamidis and technetium-scintigraphy on the diagnosis of ATTR cardiomyopathy.

Methods: Ten institutes participated in this study on the pathology consultation of amyloidosis and shared rabbit polyclonal anti-κ, anti-λ, and anti-transthyretin antibodies. Proteomic analysis was performed when the typing diagnosis by immunohistochemistry was unavailable.

Results: Out of 5400 consultation cases received from April 2018 to July 2022, the type of amyloidosis by immunohistochemistry was determined in 4119 of the 4420 Congo-red positive cases. The incidences of AA, ALκ, ALλ, ATTR, Aβ2M and others were 3.2, 11.3, 28.3, 54.9, 0.6 and 1.8%, respectively. Out of 2208 cardiac biopsy cases received, 1503 cases were ATTR positive. There were 4.0 and 4.9 times more total cases and ATTR-positive cases, respectively, in the last 12 months as compared to the first 12 months.

Conclusions: The approval of tafamidis and technetium-scintigraphy raised the awareness of ATTR cardiomyopathy, leading to an upsurge in ATTR-positive cardiac biopsy cases.