Analysis of Distal Compound Muscle Action Potential Duration in Hereditary Transthyretin Amyloidosis with Polyneuropathy

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  • HOSHINO Yumi
    Department of Medicine (Neurology and Rheumatology), Shinshu University School of Medicine
  • KODAIRA Minori
    Department of Medicine (Neurology and Rheumatology), Shinshu University School of Medicine
  • OHASHI Nobuhiko
    Department of Medicine (Neurology and Rheumatology), Shinshu University School of Medicine
  • MORITA Hiroshi
    Center for Health, Safety and Environmental Management, Shinshu University
  • SEKIJIMA Yoshiki
    Department of Medicine (Neurology and Rheumatology), Shinshu University School of Medicine Institute for Biomedical Sciences, Shinshu University

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Background : Hereditary transthyretin (ATTRv) amyloidosis, a disorder accompanied by axonal polyneuropathy, is often misdiagnosed as chronic inflammatory demyelinating polyneuropathy (CIDP). Prolongation of distally evoked compound muscle action potential duration (DCMAPD), an electrophysiological parameter of heterogeneous conduction delay at the distal part of the motor nerve suggesting demyelinating neuropathies, is included in an index of diagnostic criteria for CIDP. However, DCMAPDs are strongly influenced by low-frequency filtering (LFF) settings, which differ across hospitals worldwide.<br>Aim : To analyze DCMAPD in patients with ATTRv amyloidosis with polyneuropathy (ATTRv-PN).<br>Methods : DCMAPs of the median, ulnar, tibial, and peroneal nerves were recorded under LFF settings of 2, 10, and 20 Hz in 50 patients with ATTRv-PN. The changes of DCMAPD accompanied with the changes of LFF settings were analyzed. The appropriateness of the cut-off values of the DCMAPD in the latest criteria for CIDP, which defined under various LFF settings, was also validated in ATTRv-PN patients.<br>Results : The DCMAPD was shorter with increasing LFF settings. Less than 10％ of patients with ATTRv-PN demonstrated prolonged DCMAPD of the ulnar, tibial, and peroneal nerves. In contrast, ten patients demonstrated prolonged DCMAPD in the median nerve under LFF settings of 2, 10, and/or 20 Hz. Nine of the ten cases were complicated with carpal tunnel syndrome (CTS).<br>Conclusion : Prolongation of DCMAPDs in the ulnar, tibial, and peroneal nerves is rare in ATTRv-PN patients. DCMAPD analysis of the median nerve in patients with ATTRv-PN requires caution, because they frequently develop CTS and those with CTS may demonstrate prolonged DCMAPD.

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