P71-S Transthyretin familial amyloid polyneuropathy (TTR-FAP). Neurophysiological assessment in asymptomatic carriers

Background Transthyretin familial amyloid polyneuropathy (TTR-FAP) is a rare hereditary disorder caused by mutations in the TTR gene. Unless treated, its course is very severe and death occurs after 7–10 years of symptoms onset. Genetic counseling is crucial in the detection of asymptomatic carriers, and scientific societies recommend a thorough examination and follow-up to detect the onset of the disease and indication of treatment. The aim of the study is to evaluate the usefulness of neurophysiological tests to detect the onset of polyneuropathy in asymptomatic carriers of the TTR mutation. Material and methods Asymptomatic carriers of the TTR mutation were selected. Clinical and neurophysiological evaluation were performed every 12 months. Motor and sensory nerve conduction studies (NCS) were used to evaluate thick nerve fiber in upper and lower limbs. The study of fine nerve fiber included the variation of the RR interval, cutaneous sympathetic response (SSR) by electrical stimulation, Sudoscan, and the study of thermal and algic thresholds by quantitative sensory test (QST) in the hands and feet. Results Nineteen asymptomatic carriers of the TTR mutation have been included (13 men and 6 women) and followed for an average of 5 years. Four of them developed some abnormality in the QST, 4 developed carpal tunnel syndrome, and 5 showed some abnormality of SSR and QST of uncertain significance. The sudoscan test provided greater sensitivity than the SSR. Conclusion The neurophysiological study of fine nerve fiber is a useful method in the follow-up of asymptomatic patients carrying TTR mutation.