Footnotes

• MAEC and NT contributed equally to this work.

• Acknowledgements The authors thank Dr Takashi Kanda (Yamaguchi University) and Hitoshi Nukada (University of Otago) for valuable comments.

• Contributors MAEC analysed the data and wrote the draft. NT performed sonography. HN planned the project, interpreted the data and edited the manuscript. AM, NM, NO, HK and AK evaluated the patients and performed electrophysiological tests. MU, RT, YI and RK edited the manuscript.

• Funding This work was supported (in part) by Grants-in-Aid from the Research on Measures for Intractable Diseases and a Health and Labour Sciences Research Grant on Rare and Intractable Diseases (Evidence-based Early Diagnosis and Treatment Strategies for Neuroimmunological Diseases) from the Ministry of Health, Labour and Welfare of Japan.

• Competing interests None declared.

• Patient consent Obtained.

• Ethics approval Tokushima University and Kyoto University Hospitals.

• Provenance and peer review Not commissioned; externally peer reviewed.