The diagnostic accuracy of Sudoscan in transthyretin familial amyloid polyneuropathy

•Assessment of autonomic function is critical in the diagnosis of transthyretin familial amyloid polyneuropathy (TTR-FAP).•Feet electrochemical skin conductance was a significant independent predictor for the presence of symptoms and autonomic dysfunction in TTR-FAP.•Sudoscan showed a good sensitivity and specificity in the early diagnosis of TTR-FAP.

ObjectiveTransthyretin familial amyloid polyneuropathy (TTR-FAP) is an axonal sensory-motor and autonomic neuropathy. Reliable quantification of sudomotor function could prove essential in the diagnosis and early treatment management. We aim to assess the diagnostic value of a new sudomotor test (Sudoscan) in TTR-FAP.MethodsOne hundred and thirty-three TTR-FAP Val30Met carriers, divided in asymptomatic and symptomatic stage 1, were compared with 37 healthy controls. We analyzed the right sural sensory nerve action potential (SNAP), the plantar sympathetic skin response (SSR) and the electrochemical skin conductance (ESC) measured by Sudoscan in both hands and feet.ResultsAll neurophysiological measures were significantly worse in the symptomatic group. However, feet ESC was the only test distinguishing symptomatic patients with autonomic dysfunction from those without autonomic dysfunction, and both groups from asymptomatic subjects and healthy controls. Feet ESC was a significant independent predictor for the presence of symptoms and autonomic failure, after adjusting for demographic characteristics, sural SNAP and SSR amplitudes (p < 0.05). Feet ESC showed 76% sensitivity and 85% specificity for detection of dysautonomia.ConclusionFeet ESC is a sensitive test to assess early autonomic dysfunction in TTR-FAP subjects. This investigation should be considered for routine assessment in this population.SignificanceAbnormal feet responses on Sudoscan support early diagnosis in TTR-FAP.