Peripheral nerve ultrasonography in patients with transthyretin amyloidosis

Objective: To systematically study peripheral nerve morphology in patients with transthyretin (TTR) amyloidosis and TTR gene mutation carriers using high-resolution ultrasonography (US).

Methods: In this prospective cross-sectional study we took a structured history, performed neurological examination, and measured peripheral nerve cross-sectional areas (CSAs) bilaterally at 28 standard locations using US. Demographic and US findings were compared to controls.

Results: Peripheral nerve CSAs were significantly larger in 33 patients with familial amyloid polyneuropathy (FAP) compared to 50 controls, most dramatically at the common entrapment sites (median nerve at the wrist, ulnar nerve at the elbow), and in the proximal nerve segments (median nerve in the upper arm, sciatic nerve in the thigh). Findings in 21 asymptomatic TTR gene mutation carriers were less marked compared to controls, with CSAs being larger only in the median nerve in the upper arm. Nerve CSAs correlated with abnormalities on nerve conduction studies.

Conclusion: Using US, we confirmed previous pathohistological and imaging reports in FAP of the most pronounced peripheral nerve thickening in the proximal limb segments.

Significance: Similar to US findings in diabetic and vasculitic neuropathies these predominantly proximal locations of nerve thickening may be attributed to ischaemic nerve damage caused by poor perfusion in the watershed zones along proximal limb segments.