Nodular amyloid deposits with collagen fibre rupture in tenosynovial carpal tissues are associated with transthyretin cardiomyopathy: a single-centre prospective diagnostic study

Systemic amyloidosis affects various organs, including soft tissues, with cardiac involvement (ATTR-CM) associated with the poorest prognosis. Because current treatments are most effective in the early stages, early diagnosis is essential. However, little is known about the significance of distinct morphological patterns of amyloid deposits in musculoskeletal red flag lesions, including the bilateral carpal tunnel tissues. The primary objective of this study was to evaluate the incidence and morphological patterns of amyloidosis in patients with bilateral carpal tunnel syndrome; the secondary aim was to screen for cardiac forms. We proposed a novel three-tiered histopathological classification of amyloid deposits within carpal tenosynovial tissues. From June 2021 until May 2023, we conducted a single-centre prospective diagnostic study to investigate microscopic patterns of amyloid deposits in tenosynovial tissues obtained during open median nerve release surgery in patients with bilateral carpal tunnel syndrome. Our study cohort included 83 patients (42 women, 41 men), with a mean age of 65.7 years (range, 27–89 years). All patients underwent a cardiac examination. Scintigraphy and endomyocardial biopsy were performed in highly suspicious cases. Amyloid deposits were identified in Congo red-stained specimens from 24 patients (28.9%; 16 men and 8 women) and categorised as linear (n = 12), nodular (n = 5), or nodular with collagen fibre rupture (n = 7). The semiquantitative assessed amyloid burden did not correlate with the histologic types of amyloid. Scintigraphy and endomyocardial biopsy were performed in three male patients and confirmed a wild-type form of ATTR-CM. All three patients showed type 3 nodular amyloid deposits with collagen rupture in their carpal tissues. Although the extent of amyloid deposition in tenosynovial tissues did not correlate with cardiac involvement, we observed an association between the nodular pattern with collagen fibre rupture (type 3) and the presence of wild-type ATTR-CM. We defined three distinct morphological types of amyloid deposition in tenosynovial tissues. The type 3 nodular pattern with collagen fibre rupture appeared to be associated with ATTR-CM. This proposed histopathological classification might significantly enhance screening for ATTR-CM in patients with bilateral carpal tunnel syndrome. Our exploratory findings require validation in larger studies.