Correlation between a commercial electrophysiological test of sudomotor function and intraepidermal nerve fiber density in hereditary transthyretin amyloidosis

Introduction/aims: In the early stage, hereditary transthyretin (ATTRv) amyloidosis predominantly affects small nerve fibers, resulting in autonomic dysfunction and impaired sensation of pain and temperature. Evaluation of small fiber neuropathy (SFN) is therefore important for early diagnosis and treatment of ATTRv amyloidosis. Herein, we aimed to investigate the accuracy of a quick and non-invasive commercial sudomotor function test (SFT) for the assessment of SFN in ATTRv amyloidosis.Methods: We performed the SFT in 39 Japanese adults with ATTRv amyloidosis, and we analyzed the correlations between electrochemical skin conductance (ESC) values obtained via the SFT and the parameters of other neuropathy assessment methods.Results: ESC in the feet demonstrated significant, moderate correlations with intraepidermal nerve fiber density (IENFD) results (Spearman's rank correlation coefficient [r(s) ], 0.58; p < .002) and other neuropathy assessment methods including the sensory nerve action potential amplitude in the nerve conduction studies (r(s) , 0.52; p < .001), the Neuropathy Impairment Score (r(s) , -0.45; p < .01), the heat-pain detection threshold (r(s) , -0.62; p < .0001), and the autonomic section of the Kumamoto ATTRv clinical score (r(s) , -0.53; p < .0001).Discussion: In this study, we found that ESC values in the feet via the SFT demonstrated significant, moderate correlations with IENFD and other SFN assessment methods in patients with ATTRv amyloidosis, suggesting that the SFT appears to be an appropriate method for assessment of SFN in this disease.