Peripheral Nerve Ultrasound Findings in Hereditary Transthyretin Amyloidosis in Brazil.

Background/Objectives: Hereditary transthyretin amyloidosis (ATTRv) is an autosomal dominant disorder characterized by systemic deposition of amyloid fibrils, leading to peripheral neuropathy and multisystemic involvement. Peripheral nerve ultrasound is a promising tool for detecting structural nerve changes, yet its use in Latin American populations is limited. This study aimed to characterize nerve ultrasound findings in Brazilian patients with ATTRv. Methods: We conducted a cross-sectional study of 72 genetically confirmed ATTRv individuals from two Brazilian centers. Participants were classified into symptomatic patients with polyneuropathy (n = 31) and asymptomatic TTR variant carriers (n = 41). All participants underwent a standardized neurological examination, and nerve ultrasound was used to assess the median nerve, brachial plexus, and C6 root. Cross-sectional areas (CSAs) from the right side were used for analysis and compared to reference values. Results: Symptomatic patients showed increased CSAs in the median nerve (wrist: 10.17 mm2, arm: 9.8 mm2), C6 root (8.55 mm2), and brachial plexus (70.82 mm2; all p < 0.05), but not in the forearm. Notably, asymptomatic carriers exhibited nerve enlargement in the median nerve at the wrist, the C6 root, and the brachial plexus, despite lacking clinical signs of neuropathy. Peripheral nerve enlargement in ATTRv affects both symptomatic patients and asymptomatic carriers, with a predilection for proximal and entrapment sites. Conclusions: These findings support the utility of nerve ultrasound as a non-invasive biomarker for early nerve involvement in ATTRv. Further studies are warranted to validate its role in disease monitoring and guide therapeutic interventions, especially in genetically at-risk populations.