Electromyographic findings in transthyretin (TTR)-related familial amyloid polyneuropathy (FAP).

Affected members and asymptomatic relatives of 9 Italian families with transthyretin (TTR)-related hereditary amyloidosis carrying different TTR mutations (Met30, Pro36, Ala47, Ala49, Gln89) were followed up with repeated EMG investigations. In 3 patients, spontaneous myoclonic discharges with synkinesia were found in the facial muscles. EMG signs of chronic denervation with features of proximal neural involvement were also found in proximal limb muscles. Neuropathy worsened step-wise with progressing clinical stage. Sympathetic skin responses progressively decreased, disappearing in the late stages of the disease. Symptomatic relatives carrying the TTR mutations had significantly reduced sensory conduction velocities and amplitudes of compound motor action potentials. Follow-up studies in 3 patients after liver transplant showed progression of sensory-motor neuropathy 1 year after the transplant, and a slight improvement 18 months later. Based on our electrophysiological findings and a review of the literature, we propose that TTR-related FAP type I be considered not only a peripheral neuropathy, but also a meningoradiculopathy due to deposition of amyloidogenic TTR in the leptomeninges.