Quantitative sudomotor test helps differentiate transthyretin familial amyloid polyneuropathy from chronic inflammatory demyelinating polyneuropathy

Objective: Transthyretin familial amyloid polyneuropathy (TTR-FAP) is an aggressive hereditary neuropathy characterized by sensory and autonomic dysfunction. There are numerous reports of TTR-FAP misdiagnosed and treated as chronic inflammatory demyelinating polyneuropathy (CIDP), leading to delayed diagnosis, risk of iatrogenic adverse events and increased socio-economic costs. Quantitative sudomotor function measured by electrochemical skin conductance (ESC) appears to be a sensitive test in TTR-FAP. We aimed to evaluate the performance of ESC in differentiating TTR-FAP from CIDP. Methods: Thirty-eight patients with genetically confirmed hereditary TTR amyloidosis and 26 with definite CIDP according to the EFNS/PNS guidelines and negative TTR-FAP genetic testing were involved in this study. We compared the ESC for feet and hands measured by Sudoscan for each patient. Results: ESC (mS) was significantly lower in TTR-FAP for both hands (72 vs 45, p < 0.0001) and feet (77 vs 35, p < 0.0001). Feet ESC < 64 mS had a 89% sensitivity and a 96% specificity to differentiate between CIDP and TTR-FAP. Conclusion: Sudoscan is a fast, non-invasive and easy to perform test, able to distinguish CIDP and TTR-FAP patients with good sensitivity and specificity. Significance: Sudoscan can be helpful in distinguishing between CIDP and TTR-FAP. (C) 2020 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. All rights reserved.